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Verissimo, Kellen Matos, Louise Neiva Perez, Aline Cutrim Dragalzew, Gayani Senevirathne, Sylvain Darnet, Wainna Renata Barroso Mendes, Ciro Ariel dos Santos Neves et al. « Salamander-like tail regeneration in the West African lungfish ». Proceedings of the Royal Society B : Biological Sciences 287, no 1935 (16 septembre 2020) : 20192939. http://dx.doi.org/10.1098/rspb.2019.2939.
Texte intégralRésumé :
Salamanders, frog tadpoles and diverse lizards have the remarkable ability to regenerate tails. Palaeontological data suggest that this capacity is plesiomorphic, yet when the developmental and genetic architecture of tail regeneration arose is poorly understood. Here, we show morphological and molecular hallmarks of tetrapod tail regeneration in the West African lungfish Protopterus annectens , a living representative of the sister group of tetrapods. As in salamanders, lungfish tail regeneration occurs via the formation of a proliferative blastema and restores original structures, including muscle, skeleton and spinal cord. In contrast with lizards and similar to salamanders and frogs, lungfish regenerate spinal cord neurons and reconstitute dorsoventral patterning of the tail. Similar to salamander and frog tadpoles, Shh is required for lungfish tail regeneration. Through RNA-seq analysis of uninjured and regenerating tail blastema, we show that the genetic programme deployed during lungfish tail regeneration maintains extensive overlap with that of tetrapods, with the upregulation of genes and signalling pathways previously implicated in amphibian and lizard tail regeneration. Furthermore, the lungfish tail blastema showed marked upregulation of genes encoding post-transcriptional RNA processing components and transposon-derived genes. Our results show that the developmental processes and genetic programme of tetrapod tail regeneration were present at least near the base of the sarcopterygian clade and establish the lungfish as a valuable research system for regenerative biology.
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Sutro, J. B. « Kinetics of veratridine action on Na channels of skeletal muscle. » Journal of General Physiology 87, no 1 (1 janvier 1986) : 1–24. http://dx.doi.org/10.1085/jgp.87.1.1.
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Veratridine bath-applied to frog muscle makes inactivation of INa incomplete during a depolarizing voltage-clamp pulse and leads to a persistent veratridine-induced Na tail current. During repetitive depolarizations, the size of successive tail currents grows to a plateau and then gradually decreases. When pulsing is stopped, the tail current declines to zero with a time constant of approximately 3 s. Higher rates of stimulation result in a faster build-up of the tail current and a larger maximum value. I propose that veratridine binds only to open channels and, when bound, prevents normal fast inactivation and rapid shutting of the channel on return to rest. Veratridine-modified channels are also subject to a "slow" inactivation during long depolarizations or extended pulse trains. At rest, veratridine unbinds with a time constant of approximately 3 s. Three tests confirm these hypotheses: (a) the time course of the development of veratridine-induced tail currents parallels a running time integral of gNa during the pulse; (b) inactivating prepulses reduce the ability to evoke tails, and the voltage dependence of this reduction parallels the voltage dependence of h infinity; (c) chloramine-T, N-bromoacetamide, and scorpion toxin, agents that decrease inactivation in Na channels, each greatly enhance the tail currents and alter the time course of the appearance of the tails as predicted by the hypothesis. Veratridine-modified channels shut during hyperpolarizations from -90 mV and reopen on repolarization to -90 mV, a process that resembles normal activation gating. Veratridine appears to bind more rapidly during larger depolarizations.
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AFONSO, Andre Muniz, Ana Beatriz Monteiro FONSECA, Carlos Adam CONTE-JUNIOR, Eliane Teixeira MÁRSICO, Mônica Queiroz FREITAS et Sergio Borges MANO. « Frog tail : a source of protein to feed the future ». Boletim do Instituto de Pesca 43, no 1 (30 mars 2017) : 112–23. http://dx.doi.org/10.20950/1678-2305.2017v43n1p112.
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Bennett, A. M., et D. L. Murray. « Carryover effects of phenotypic plasticity : embryonic environment and larval response to predation risk in Wood Frogs (Lithobates sylvaticus) and Northern Leopard Frogs (Lithobates pipiens) ». Canadian Journal of Zoology 93, no 11 (novembre 2015) : 867–77. http://dx.doi.org/10.1139/cjz-2015-0129.
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Limitations of phenotypic plasticity affect the success of individuals and populations in changing environments. We assessed the plasticity-history limitation on predator-induced defenses in anurans (Wood Frogs, Lithobates sylvaticus (LeConte, 1825), and Northern Leopard Frogs, Lithobates pipiens (Schreber, 1782)), predicting that plastic responses to predation risk by dragonfly larvae (family Aeshnidae) in the embryonic environment would limit the defensive response to predators in the larval environment. Predator-conditioned Wood Frog embryos increased relative tail depth in response to those same cues as larvae, whereas predator-naive tadpoles did not. However, no carryover effect was noted in the behavioural response of Wood Frog tadpoles to predation risk. Predator-naive Northern Leopard Frog tadpoles increased relative tail depth in response to predation risk in the larval environment. Predator-conditioned Northern Leopard Frog embryos hatched with, and maintained, a marginal increase in tail depth as larvae in the absence of predation risk. Predator-conditioned Northern Leopard Frog embryos exposed to predation risk as larvae showed no morphological response. While we find no strong support for the plasticity-history limitation per se, carryover effects across embryonic and larval life-history stages were noted in both Wood Frog and Northern Leopard Frog, suggesting that predation risk early in ontogeny can influence the outcome of future interactions with predators.
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Brinckerhoff, Constance E., et Lynn M. Matrisian. « Matrix metalloproteinases : a tail of a frog that became a prince ». Nature Reviews Molecular Cell Biology 3, no 3 (mars 2002) : 207–14. http://dx.doi.org/10.1038/nrm763.
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SILVA-SOARES, THIAGO, PAULO NOGUEIRA COSTA, RODRIGO B. FERREIRA et LUIZ NORBERTO WEBER. « The tadpole of the hylid frog Scinax belloni (Anura : Hylidae) ». Zootaxa 2727, no 1 (23 janvier 2019) : 63. http://dx.doi.org/10.11646/zootaxa.2727.1.6.
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Scinax perpusillus group is composed by11 species. Only Scinax arduous, Scinax littoreus, Scinax. meloi, S. perpusillus, S. tupinamba, and S. v-signatus, have its tadpole described. Herein we described the tadpole of Scinax belloni and its internal oral features. Tadpoles of S. belloni were collected in bromeliads at the Parque Estadual do Forno Grande, municipality of Castelo, Espírito Santo, southeastern. Two tadpoles were reared to froglets in order to allow specific identification. The morphology of S. belloni tadpoles resemble the other known larvae in many aspects such as oval body in dorsal view, coloration, rounded snout in dorsal view, dorsolateral eyes, anteroventral mouth and labial tooth row formula 2(2)/3. In fact, at first sight, all known tadpoles are very similar from each other. Nevertheless, they do can be distinguished by some characters as the shape of lower jaw; number of row of labial papillae; the size of the fins; height of tail and the body; whether musculature of tail reaches its tip and if tail ends rounded or pointed. S. belloni tadpoles are readily differentiated from the other known Scinax gr. perpusillus species tadpoles by the presence of a dark band that goes along the dorsal and ventral fin. The internal oral morphology of S. belloni is also described.
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Vitt, Laurie J., et William E. Cooper Jr. « Tail loss, tail color, and predator escape in Eumeces (Lacertilia : Scincidae) : age-specific differences in costs and benefits ». Canadian Journal of Zoology 64, no 3 (1 mars 1986) : 583–92. http://dx.doi.org/10.1139/z86-086.
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The tail loss adaptation in Eumeces of the southeastern United States is complex. Juveniles possess tails that are colored differently from those of adults and apparently distract the attention of potential predators from the body to the tail. Adult tails are cryptically colored. Frequency of tail loss is high across size groups. Experiments on growth of tailed and tailless juveniles suggest no effect of tail loss on growth and, thus, there may be little cost of tail loss to juveniles other than the temporary loss of the autotomy adaptation. Lipids in adult tails constitute nearly 50% of total standing lipids and are reduced during reproduction similar to other lipid reserves. This suggests that tail loss in adults is expensive, particularly prior to or during the breeding season. We suggest that the high costs of tail loss in Eumeces are offset by the increased probability of predator escape via tail loss. Tail loss data are minimal estimates of escape via distraction of a predator's attack to the tail as indicated by predation experiments. The presence, coloration, and behaviors of the tail may result in a high proportion of predation attempts being redirected to the tail followed by total misses.
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Joshy, Hareesh, et Mitsuru Kuramoto. « Scanning electron microscopic studies on spermatozoa of anurans from India and Sri Lanka ». Amphibia-Reptilia 22, no 3 (2001) : 303–8. http://dx.doi.org/10.1163/156853801317050098.
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AbstractThe shape and size of spermatozoa of 11 frog species from India and Sri Lanka were examined by scanning electron microscopy. The spermatozoa of the genera Limnonectes and Euphlyctis were of the generalized type with a thick sperm head and a thin tail, whereas Indirana semipalmata had peculiar spermatozoa with a densely coiled sperm head and a thick tail. Rhacophorus microtympanum is likely to belong to the genus Philautus from sperm morphology. The spermatozoa of Microhyla ornata and Ramanella obscura were very similar, with a cone-shaped sperm head and a thin tail.
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VON SECKENDORFF HOFF, KARIN, et RICHARD JOEL WASSERSUG. « The Kinematics of Swimming in Larvae of the Clawed Frog, Xenopus Laevis ». Journal of Experimental Biology 122, no 1 (1 mai 1986) : 1–12. http://dx.doi.org/10.1242/jeb.122.1.1.
Texte intégralRésumé :
The kinematics of swimming in larval Xenopus laevis has been studied using computer-assisted analysis of high-speed (200 frames s−1) ciné records. The major findings are as follows. 1. At speeds below 6 body lengths (L) per second, tail beat frequency is approximately 10 Hz and, unlike for most aquatic vertebrates, is not correlated with specific swimming speed. At higher speeds, tail beat frequency and speed are positively correlated. 2. Xenopus tadpoles show an increase in the maximum amplitude of the tail beat with increasing velocity up to approximately 6Ls−1. Above that speed amplitude approaches an asymptote at 20 % of body length. 3. Anterior yaw is absent at velocities below 6Ls−1, unlike for other anuran larvae, but is present at higher speeds. 4. At speeds below 6Ls−1 there is a positive linear relationship between length of the propulsive wave (λ) and specific swimming speed. At higher speeds wavelength is constant at approximately 0.8L. 5. There is a shift in the modulation of wavelength and tail beat frequency with swimming speed around 5.6Ls−1, suggesting two different swimming modes. The slower mode is used during open water cruising and suspension feeding. The faster, sprinting mode may be used to avoid predators. 6. Froude efficiencies are similar to those reported for fishes and other anuran larvae. 7. Unlike Rana and Bufo larvae, the axial muscle mass of Xenopus increases dramatically with size from less than 10% of total mass for the smallest animals to more than 45% of total mass for the largest animals. This increase is consistent with maintaining high locomotor performance throughout development.
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Schwaner, M. Janneke, Grace A. Freymiller, Rulon W. Clark et Craig P. McGowan. « How to Stick the Landing : Kangaroo Rats Use Their Tails to Reorient during Evasive Jumps Away from Predators ». Integrative and Comparative Biology 61, no 2 (3 mai 2021) : 442–54. http://dx.doi.org/10.1093/icb/icab043.
Texte intégralRésumé :
Synopsis Tails are widespread in the animal world and play important roles in locomotor tasks, such as propulsion, maneuvering, stability, and manipulation of objects. Kangaroo rats, bipedal hopping rodents, use their tail for balancing during hopping, but the role of their tail during the vertical evasive escape jumps they perform when attacked by predators is yet to be determined. Because we observed kangaroo rats swinging their tails around their bodies while airborne following escape jumps, we hypothesized that kangaroo rats use their tails to not only stabilize their bodies while airborne, but also to perform aerial re-orientations. We collected video data from free-ranging desert kangaroo rats (Dipodomys deserti) performing escape jumps in response to a simulated predator attack and analyzed the rotation of their bodies and tails in the yaw plane (about the vertical-axis). Kangaroo rat escape responses were highly variable. The magnitude of body re-orientation in yaw was independent of jump height, jump distance, and aerial time. Kangaroo rats exhibited a stepwise re-orientation while airborne, in which slower turning periods corresponded with the tail center of mass being aligned close to the vertical rotation axis of the body. To examine the effect of tail motion on body re-orientation during a jump, we compared average rate of change in angular momentum. Rate of change in tail angular momentum was nearly proportional to that of the body, indicating that the tail reorients the body in the yaw plane during aerial escape leaps by kangaroo rats. Although kangaroo rats make dynamic 3D movements during their escape leaps, our data suggest that kangaroo rats use their tails to control orientation in the yaw plane. Additionally, we show that kangaroo rats rarely use their tail length at full potential in yaw, suggesting the importance of tail movement through multiple planes simultaneously.
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Polanski, Arnold, Evarist Stoja et Frank Windmeijer. « Telling tales from the tails : High‐dimensional tail interdependence ». Journal of Applied Econometrics 34, no 5 (22 mai 2019) : 779–94. http://dx.doi.org/10.1002/jae.2708.
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Hasegawa, Masaru, Emi Arai et Masahiko Nakamura. « Experimental tail shortening affects feeding rate depending on original tail length in female barn swallows Hirundo rustica gutturalis ». Journal of Ethology 38, no 2 (21 janvier 2020) : 179–84. http://dx.doi.org/10.1007/s10164-019-00637-y.
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AbstractLong tail feathers of the barn swallow Hirundo rustica are a classic example of an intersexually selected trait, but previous aerodynamic analyses indicate that the tail feather is only 10–12 mm longer than the aerodynamic optimum even in the nominate subspecies with long tails. Here, by experimentally shortening female tail length, we studied the feeding cost of long tail feathers in Japanese barn swallows, Hirundo rustica gutturalis, which have ca. 10 mm shorter tails than the nominate subspecies. Female feeding rate was explained by the interaction between treatment and original female tail length: feeding rate decreased with decreasing original female tail length in control, but not in tail-shortened females. Because the interaction term was far from significant in the analysis of female incubation investment, the observed pattern would be specific to feeding rate, which is greatly affected by the aerodynamic properties associated with tail length. Differential allocation of paternal feeding investment was not observed in the current data set. Long tails would be costly at least in short-tailed females, supporting differential costs of ornamentation as predicted by sexual selection theory. Female outermost tail feathers are costly ornamentation in short-tailed Japanese barn swallows.
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Mohanty-Hejmadi, Priyambada, et Pravati Kumari Mahapatra. « Studies on tail regeneration and homeotic transformation in anuran tadpoles ». International Journal of Developmental Biology 64, no 1-2-3 (2020) : 65–70. http://dx.doi.org/10.1387/ijdb.190230pm.
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Anuran tadpoles are excellent models for regeneration studies. The tail, an organ essential for swimming for the aquatic tadpole, regenerates completely following injury or amputation. However, treatment with the morphogen, vitamin A or retinoic acid inhibits normal tail regeneration and induces homeotic transformation of tail to limbs. This phenomenon was discovered for the first time in the Indian marbled balloon frog Uperodon systoma in the Developmental Biology laboratory of Utkal University (Odisha, India) in the year 1992. In this paper, we present the results of morphological, histological, biochemical and molecular (immonohistochemistry) investigations of vitamin A induced homeotic transformation in different anuran species. In addition, we discuss the putative role of fibroblast growth factor 1 during spinal cord regeneration in the tadpoles of the Indian tree frog, Polypedates maculatus, an ideal model for regeneration studies in an Indian context.
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Cathomen, Toni, Hussein Y. Naim et Roberto Cattaneo. « Measles Viruses with Altered Envelope Protein Cytoplasmic Tails Gain Cell Fusion Competence ». Journal of Virology 72, no 2 (1 février 1998) : 1224–34. http://dx.doi.org/10.1128/jvi.72.2.1224-1234.1998.
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ABSTRACT The cytoplasmic tail of the measles virus (MV) fusion (F) protein is often altered in viruses which spread through the brain of patients suffering from subacute sclerosing panencephalitis (SSPE). We transferred the coding regions of F tails from SSPE viruses in an MV genomic cDNA. Similarly, we constructed and transferred mutated tail-encoding regions of the other viral glycoprotein hemagglutinin (H) gene. From the mutated genomic cDNAs, we achieved rescue of viruses that harbor different alterations of the F tail, deletions in the membrane-distal half of the H tail, and combinations of these mutations. Viruses with alterations in any of the tails spread rapidly through the monolayer via enhanced cell-cell fusion. Double-tail mutants had even higher fusion competence but slightly decreased infectivity. Analysis of the protein composition of released mutant viral particles indicated that the tails are necessary for accurate virus envelope assembly and suggested a direct F tail-matrix (M) protein interaction. Since even tail-altered glycoproteins colocalized with M protein in intracellular patches, additional interactions may exist. We conclude that in MV infections, including SSPE, the glycoprotein tails are involved not only in virus envelope assembly but also in the control of virus-induced cell fusion.
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Klemelä, Jussi. « Visualization of Multivariate Data with Tail Trees ». Information Visualization 6, no 2 (janvier 2007) : 109–22. http://dx.doi.org/10.1057/palgrave.ivs.9500151.
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We introduce graphical tools to visualize the shape, the location, and the orientation of a multivariate data set. We define a tree structure among the observations, called a tail tree. A tail tree is a tree whose root node corresponds to a center point of the data, and whose branches correspond to the tails of the data. We visualize a tail tree with a tail tree plot. Visualizing the tree structure among the observations makes it feasible to detect features from the data. A tail tree may also be used to define and enhance other visualizations. We define a tail frequency plot which visualizes the empirical probabilities of the disconnected tails of the point cloud. A tail tree induces a segmentation of the data which may be used to enhance a grand tour, graphical matrices, and parallel coordinate plots. We apply tail tree plots in exploratory data analysis of financial data.
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Clark, Christopher James, et Robert Dudley. « Flight costs of long, sexually selected tails in hummingbirds ». Proceedings of the Royal Society B : Biological Sciences 276, no 1664 (11 mars 2009) : 2109–15. http://dx.doi.org/10.1098/rspb.2009.0090.
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The elongated tails adorning many male birds have traditionally been thought to degrade flight performance by increasing body drag. However, aerodynamic interactions between the body and tail can be substantial in some contexts, and a short tail may actually reduce rather than increase overall drag. To test how tail length affects flight performance, we manipulated the tails of Anna's hummingbirds ( Calypte anna ) by increasing their length with the greatly elongated tail streamers of the red-billed streamertail ( Trochilus polytmus ) and reducing their length by removing first the rectrices and then the entire tail (i.e. all rectrices and tail covert feathers). Flight performance was measured in a wind tunnel by measuring (i) the maximum forward speed at which the birds could fly and (ii) the metabolic cost of flight while flying at airspeeds from 0 to 14 m s −1 . We found a significant interaction effect between tail treatment and airspeed: an elongated tail increased the metabolic cost of flight by up to 11 per cent, and this effect was strongest at higher flight speeds. Maximum flight speed was concomitantly reduced by 3.4 per cent. Also, removing the entire tail decreased maximum flight speed by 2 per cent, suggesting beneficial aerodynamic effects for tails of normal length. The effects of elongation are thus subtle and airspeed-specific, suggesting that diversity in avian tail morphology is associated with only modest flight costs.
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Furukawa, Ayako, Masatoshi Wakamori, Yasuhiro Arimura, Hideaki Ohtomo, Yasuo Tsunaka, Hitoshi Kurumizaka, Takashi Umehara et Yoshifumi Nishimura. « Acetylated histone H4 tail enhances histone H3 tail acetylation by altering their mutual dynamics in the nucleosome ». Proceedings of the National Academy of Sciences 117, no 33 (3 août 2020) : 19661–63. http://dx.doi.org/10.1073/pnas.2010506117.
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The structural unit of eukaryotic chromatin is a nucleosome, comprising two histone H2A-H2B heterodimers and one histone (H3-H4)2tetramer, wrapped around by ∼146 bp of DNA. The N-terminal flexible histone tails stick out from the histone core and have extensive posttranslational modifications, causing epigenetic changes of chromatin. Although crystal and cryogenic electron microscopy structures of nucleosomes are available, the flexible tail structures remain elusive. Using NMR, we have examined the dynamics of histone H3 tails in nucleosomes containing unmodified and tetra-acetylated H4 tails. In unmodified nucleosome, the H3 tail adopts a dynamic equilibrium structure between DNA-contact and reduced-contact states. In acetylated H4 nucleosome, however, the H3 tail equilibrium shifts to a mainly DNA-contact state with a minor reduced-contact state. The acetylated H4 tail is dynamically released from its own DNA-contact state to a reduced-contact state, while the H3 tail DNA-contact state becomes major. Notably, H3 K14 in the acetylated H4 nucleosome is much more accessible to acetyltransferase Gcn5 relative to unmodified nucleosome, possibly due to the formation of a favorable H3 tail conformation for Gcn5. In summary, each histone tail adopts a characteristic dynamic state but regulates one other, probably creating a histone tail network even on a nucleosome.
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Rakhmiyati, Rakhmiyati, et Muhammad Ja’far Luthfi. « Alizarin Red S-Alcian Blue Staining for Regenerated tail of Common House Gecko (Hemidactylus frenatus) ». Biology, Medicine, & ; Natural Product Chemistry 7, no 2 (31 octobre 2018) : 57–59. http://dx.doi.org/10.14421/biomedich.2018.72.57-59.
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Common House Gecko (Hemidactylus frenatus) is one of reptiles that have ability to autotomy their tails. Tail autotomy is a mechanism to protect it self from predators. After the tail broke, there will be wound healing on the tail which is then followed by a tail regeneration event. Original tail and regenerate tail is very different morphologically and anatomically. The original tail is composed of bones while the tail of the regenerate is composed of cartilage. Histochemical staining using Alizarin Red-S Alcian Blue was done to differentiate bone and cartilage. This method will stained bones red while the cartilage will stained blue.
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Kamata, Tetsuji, Makoto Handa, Yohko Kawai, Yasuo Ikeda et Sadakazu Aiso. « Regulatory Role of the Extracellular α-Tail/β-Tail Interaction in αIIbβ3 Integrin Activation ». Blood 116, no 21 (19 novembre 2010) : 3199. http://dx.doi.org/10.1182/blood.v116.21.3199.3199.
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Abstract Abstract 3199 The platelet αIIbβ3 integrin changes its conformation to increase the affinity for ligands upon platelet activation. It has been shown that binding of the intracellular proteins to the cytoplasmic tails activate αIIbβ3 by disrupting the endogenous interaction between the two cytoplasmic tails in inside-out signaling. However, the mechanism how separation of the cytoplasmic tails initiate structural rearrangement of the extracellular domains has not been investigated. In αIIbβ3 crystal structure, the α-extracellular tail consisting of thigh, calf-1, and calf-2 domains makes large interface with the β-extracellular tail consisting of EGF-2, -3, -4, and βT domains. We have previously shown that clasp formation between the two extracellular tails completely abrogated αIIbβ3 activation induced by the cytoplasmic tail truncation. This suggests that separation of the two extracellular tails is essential for activation induced by inside-out signaling. To examine whether this is the case, N-glycan binding sites consisting of the N-X-T/S motif were introduced in αIIb amino acid residues located in the thigh/EGF-2, calf-1/EGF-3, or calf-2/βT interfaces. Attachment of a bulky N-glycan to these sites would prevent endogenous interface formation, thus forces the tails to separate from each other. When expressed in CHO cells, Q513NKT mutation in the thigh, M660NRT mutation in the calf-1, V760NVT mutation in the calf-2 domain all induced robust fibrinogen binding without any activators. Attachment of N-glycan was confirmed by SDS-PAGE analysis on the αIIb fragments carrying these mutations. This activation was inhibited by stabilizing the β-head/β-tail interface or by limiting the αIIb movement with artificially introduced disulfides, both of which prevents integrin from assuming the extended conformer. Prevention of the hybrid domain swing-out also completely inhibited activation. These results suggest that separation of the tails activate αIIbβ3 by inducing integrin extension. To confirm if endogenous α-tail/β-tail interaction indeed keeps integrin in low affinity state, αIIb amino acid residues that participate in the interface formation were mutated and the effect on fibrinogen binding was examined. Among the mutants, the K514A in the thigh, R671A in the calf-1, and R751A in the calf-2 domains induced only weak activation. However, combining these mutations resulted in robust activation. This activation was completely inhibited by the C-terminal clasp formation. Taken together, these results suggest that the α-tail/β-tail interface is kept by a group of key interdomain interaction that individually is not strong enough to do so. In conclusion, the α-tail/β-tail interface interaction regulates integrin activation by keeping integrin in low affinity state. Disruption of the interaction induces separation of the extracellular tails and activates integrin by initiating the structural rearrangement from the low affinity bent conformer to the high affinity extended conformer. Disclosures: No relevant conflicts of interest to declare.
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Fish, Frank E., Natalia Rybczynski, George V. Lauder et Christina M. Duff. « The Role of the Tail or Lack Thereof in the Evolution of Tetrapod Aquatic Propulsion ». Integrative and Comparative Biology 61, no 2 (9 mai 2021) : 398–413. http://dx.doi.org/10.1093/icb/icab021.
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Abstract Secondary aquatic vertebrates exhibit a diversity of swimming modes that use paired limbs and/or the tail. Various secondarily aquatic tetrapod clades, including amphibians, reptiles, and mammals use transverse undulations or oscillations of the tail for swimming. These movements have often been classified according to a kinematic gradient that was established for fishes but may not be appropriate to describe the swimming motions of tetrapods. To understand the evolution of movements and design of the tail in aquatic tetrapods, we categorize the types of tails used for swimming and examine swimming kinematics and hydrodynamics. From a foundation of a narrow, elongate ancestral tail, the tails used for swimming by aquatic tetrapods are classified as tapered, keeled, paddle, and lunate. Tail undulations are associated with tapered, keeled, and paddle tails for a diversity of taxa. Propulsive undulatory waves move down the tail with increasing amplitude toward the tail tip, while moving posteriorly at a velocity faster than the anterior motion of the body indicating that the tail is used for thrust generation. Aquatic propulsion is associated with the transfer of momentum to the water from the swimming movements of the tail, particularly at the trailing edge. The addition of transverse extensions and flattening of the tail increases the mass of water accelerated posteriorly and affects vorticity shed into the wake for more aquatically adapted animals. Digital Particle Image Velocimetry reveals that the differences were exhibited in the vortex wake between the morphological and kinematic extremes of the alligator with a tapering undulating tail and the dolphin with oscillating wing-like flukes that generate thrust. In addition to exploring the relationship between the shape of undulating tails and the swimming performance across aquatic tetrapods, the role of tail reduction or loss of a tail in aquatic-tetrapod swimming was also explored. For aquatic tetrapods, the reduction would have been due to factors including locomotor and defensive specializations and phylogenetic and physiological constraints. Possession of a thrust-generating tail for swimming, or lack thereof, guided various lineages of secondarily aquatic vertebrates into different evolutionary trajectories for effective aquatic propulsion (i.e., speed, efficiency, and acceleration).
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Wallgren, Lundeheim, Wallenbeck, Westin et Gunnarsson. « Rearing Pigs with Intact Tails—Experiences and Practical Solutions in Sweden ». Animals 9, no 10 (15 octobre 2019) : 812. http://dx.doi.org/10.3390/ani9100812.
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Tail biting is a common issue within commercial pig production. It is mainly an indicator of inadequate housing environment and results in reduced health welfare and production. To reduce the impact of tail biting, pigs are commonly tail docked, without pain relief, within the first week of life. EU Council Directive 2008/120/EC prohibits routine tail docking, but the practice is still widely used in many Member States. Sweden has banned tail docking since 1988 and all pigs have intact tails, yet tail biting is a minor problem. This paper summarises and synthesises experimental findings and practical expertise in production of undocked pigs in Sweden and describes solutions to facilitate a transition to producing pigs with intact tails within intensive pig production in the EU. Swedish pig housing conditions and management differ in many aspects from those in other EU Member States. Swedish experiences show that lower stocking density, provision of sufficient feeding space, no fully slatted flooring, strict maximum levels for noxious gases and regular provision of litter material are crucial for success when rearing pigs with intact tails. To prevent tail biting and to eliminate the need for tail docking, we strongly recommend that EU legislation should more clearly match the biological needs of pigs, as is done in Swedish legislation.
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Bedford, Gavin S., et Keith A. Christian. « Tail morphology related to habitat of varanid lizards and some other reptiles ». Amphibia-Reptilia 17, no 2 (1996) : 131–40. http://dx.doi.org/10.1163/156853896x00162.
Texte intégralRésumé :
AbstractTail shape, length and texture were recorded from 28 species of varanid lizards as well as several other reptiles that were known to be either semi-aquatic or arboreal. The varanids were described with respect to their tail characteristics and we then looked for relationships between tail characteristics and what is known about the habitats and lifestyles of the species. Semi-aquatic species of all sizes and phylogenetic groups have laterally compressed tails with a tall "fin" comprising the dorsal one-third of the tail. The tails of the large non-aquatic varanids are laterally compressed with a coarse texture. The smaller species in the subgenus Odatria have more diverse tails, and the tail characteristics generally correspond to habitats and lifestyles. The terrestrial species that live under rocks on the soil surface have very coarse, spinous tails. Saxicolous Odattria have long, smooth tails, and arboreal species have coarse tails.
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Hu, Jie, Yu Chen et Keqi Tan. « ESTIMATION OF HIGH CONDITIONAL TAIL RISK BASED ON EXPECTILE REGRESSION ». ASTIN Bulletin 51, no 2 (15 février 2021) : 539–70. http://dx.doi.org/10.1017/asb.2021.3.
Texte intégralRésumé :
AbstractAssessing conditional tail risk at very high or low levels is of great interest in numerous applications. Due to data sparsity in high tails, the widely used quantile regression method can suffer from high variability at the tails, especially for heavy-tailed distributions. As an alternative to quantile regression, expectile regression, which relies on the minimization of the asymmetric l2-norm and is more sensitive to the magnitudes of extreme losses than quantile regression, is considered. In this article, we develop a new estimation method for high conditional tail risk by first estimating the intermediate conditional expectiles in regression framework, and then estimating the underlying tail index via weighted combinations of the top order conditional expectiles. The resulting conditional tail index estimators are then used as the basis for extrapolating these intermediate conditional expectiles to high tails based on reasonable assumptions on tail behaviors. Finally, we use these high conditional tail expectiles to estimate alternative risk measures such as the Value at Risk (VaR) and Expected Shortfall (ES), both in high tails. The asymptotic properties of the proposed estimators are investigated. Simulation studies and real data analysis show that the proposed method outperforms alternative approaches.
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YAMANOUCHI, Jun, Takaaki HATO, Tatsushiro TAMURA et Shigeru FUJITA. « Suppression of integrin activation by the membrane-distal sequence of the integrin alphaIIb cytoplasmic tail ». Biochemical Journal 379, no 2 (15 avril 2004) : 317–23. http://dx.doi.org/10.1042/bj20031753.
Texte intégralRésumé :
Integrin cytoplasmic tails regulate integrin activation including an increase in integrin affinity for ligands. Although there is ample evidence that the membrane-proximal regions of the α and β tails interact with each other to maintain integrins in a low-affinity state, little is known about the role of the membrane-distal region of the α tail in regulation of integrin activation. We report a critical sequence for regulation of integrin activation in the membranedistal region of the αIIb tail. Alanine substitution of the RPP residues in the αIIb tail rendered αIIbβ3 constitutively active in a metabolic energy-dependent manner. Although an αIIb/α6Aβ3 chimaeric integrin, in which the αIIb tail was replaced by the α6A tail, was in an energy-dependent active state to bind soluble ligands, introduction of the RPP sequence into the α6A tail inhibited binding of an activation-dependent antibody PAC1. In αIIb/α6Aβ3, deleting the TSDA sequence from the α6A tail or single amino acid substitutions of the TSDA residues inhibited αIIb/α6Aβ3 activation and replacing the membrane-distal region of the αIIb tail with TSDA rendered αIIbβ3 active, suggesting a stimulatory role of TSDA in energy-dependent integrin activation. However, adding TSDA to the αIIb tail containing the RPP sequence of the membrane-distal region failed to activate αIIbβ3. These results suggest that the RPP sequence after the GFFKR motif of the αIIb tail suppresses energy-dependent αIIbβ3 activation. These findings provide a molecular basis for the regulation of energy-dependent integrin activation by α subunit tails.
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Sen, Nandini, Adrish Sen et Erich R. Mackow. « Degrons at the C Terminus of the Pathogenic but Not the Nonpathogenic Hantavirus G1 Tail Direct Proteasomal Degradation ». Journal of Virology 81, no 8 (31 janvier 2007) : 4323–30. http://dx.doi.org/10.1128/jvi.02279-06.
Texte intégralRésumé :
ABSTRACT Pathogenic hantaviruses cause two human diseases: hantavirus pulmonary syndrome (HPS) and hemorrhagic fever with renal syndrome (HFRS). The hantavirus G1 protein contains a long, 142-amino-acid cytoplasmic tail, which in NY-1 virus (NY-1V) is ubiquitinated and proteasomally degraded (E. Geimonen, I. Fernandez, I. N. Gavrilovskaya, and E. R. Mackow, J. Virol. 77: 10760-10768, 2003). Here we report that the G1 cytoplasmic tails of pathogenic Andes (HPS) and Hantaan (HFRS) viruses are also degraded by the proteasome and that, in contrast, the G1 tail of nonpathogenic Prospect Hill virus (PHV) is stable and not proteasomally degraded. We determined that the signals which direct NY-1V G1 tail degradation are present in a hydrophobic region within the C-terminal 30 residues of the protein. In contrast to that of PHV, the NY-1V hydrophobic domain directs the proteasomal degradation of green fluorescent protein and constitutes an autonomous degradation signal, or “degron,” within the NY-1V G1 tail. Replacing 4 noncontiguous residues of the NY-1V G1 tail with residues present in the stable PHV G1 tail resulted in a NY-1V G1 tail that was not degraded by the proteasome. In contrast, changing a different but overlapping set of 4 PHV residues to corresponding NY-1V residues directed proteasomal degradation of the PHV G1 tail. The G1 tails of pathogenic, but not nonpathogenic, hantaviruses contain intervening hydrophilic residues within the C-terminal hydrophobic domain, and amino acid substitutions that alter the stability or degradation of NY-1V or PHV G1 tails result from removing or adding intervening hydrophilic residues. Our results identify residues that selectively direct the proteasomal degradation of pathogenic hantavirus G1 tails. Although a role for the proteasomal degradation of the G1 tail in HPS or HFRS is unclear, these findings link G1 tail degradation to viral pathogenesis and suggest that degrons within hantavirus G1 tails are potential virulence determinants.
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Niewiarowski, P. H., J. D. Congdon, A. E. Dunham, L. J. Vitt et D. W. Tinkle. « Tales of lizard tails : effects of tail autotomy on subsequent survival and growth of free-ranging hatchling Uta stansburiana ». Canadian Journal of Zoology 75, no 4 (1 avril 1997) : 542–48. http://dx.doi.org/10.1139/z97-067.
Texte intégralRésumé :
Potential costs and benefits of tail autotomy in lizards have been inferred almost exclusively from experimental study in semi-natural enclosures and from indirect comparative evidence from natural populations. We present complementary evidence of the costs of tail autotomy to the lizard Uta stansburiana from detailed demographic study of a natural population. On initial capture, we broke the tails of a large sample of free-ranging hatchlings (560) and left the tails of another large sample (455) intact, and then followed subsequent hatchling growth and survival over a 3-year period. Surprisingly, in 1 out of the 3 years of study, survival of female hatchlings with broken tails exceeded that of female hatchlings with intact tails. Furthermore, no effects of tail loss on survivorship were detected for male hatchlings. However, in 2 years when recaptures were very frequent (1961, 1962), growth rates of hatchlings with broken tails were significantly slower than those of their counterparts with intact tails. We discuss our results in the broader context of estimating the relative costs and benefits of tail autotomy in natural populations, and suggest that long-term demographic studies will provide the best opportunity to assess realized fitness costs and benefits with minimum bias. We also describe how experimentally induced tail autotomy can be used as a technique to complement experimental manipulation of reproductive investment in the study of life-history trade-offs.
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Baker, Michael R., et David M. Green. « Helminth parasites of native frogs (Leiopelmatidae) from New Zealand ». Canadian Journal of Zoology 66, no 3 (1 mars 1988) : 707–13. http://dx.doi.org/10.1139/z88-105.
Texte intégralRésumé :
The three native frog species of New Zealand were examined for gastrointestinal helminth parasites. Leiopelma hamiltoni was uninfected. Leiopelma hochstetteri was parasitized by the nematodes Aplectana novaezelandiae n.sp. and Cosmocerca australis n.sp. (both Cosmocercidae: Cosmocercinae), and the digenean Dolichosaccus (Lecithopyge) novaezealandiae Prudhoe, 1972 (Telorchiidae: Opisthoglyphinae). Leiopelma archeyi was infected with Cosmocerca archeyi n.sp. The three new cosmocercid species are differentiated readily from congenerics in other parts of the world by caudal features of the males and the shape of the female tail. Cosmocerca archeyi differs from C. australis in the shape of the tail in both males and females, the lack of rosette caudal papillae in males, and the possession of an unusually robust ventral somatic musculature in females. Since the native frogs from New Zealand are believed to have been isolated since the Mesozoic, the presence in them of cosmocercids that fall readily into well-established genera confirms the antiquity of the subfamily Cosmocercinae.
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Van Buskirk, J., et S. A. McCollum. « Influence of tail shape on tadpole swimming performance ». Journal of Experimental Biology 203, no 14 (15 juillet 2000) : 2149–58. http://dx.doi.org/10.1242/jeb.203.14.2149.
Texte intégralRésumé :
Many tadpoles respond to insect predators by developing deeper, and sometimes longer, tails. It has been assumed that the larger tail enhances aspects of swimming performance, because deep-tailed tadpoles survive well when confronted with hunting predators. We tested this hypothesis using both naturally occurring and surgically created variation in tail morphology of Hyla versicolor tadpoles. We measured swimming performance (maximum speed, time to reach a 2.5 cm radius, and angle of escape) and morphology (size and shape of the body and tail) in 288 tadpoles, of which half possessed the predator-induced morphology and the other half were from predator-free ponds. Large tadpoles swam faster than small ones, and shape was significantly correlated with size-corrected swimming performance. The fastest tadpoles had relatively shallow bodies and tail fins, and short tails; there was no difference in swimming performance between predator-induced and no-predator tadpoles. We performed an experiment to create independent variation in tail depth and length by surgically manipulating tail shape in 270 tadpoles. Three tail-length treatments reduced the length of the tail fin by 21 %, 34 % and 55 %; three tail-depth treatments reduced the maximum depth of the tail fin by 11 %, 34 % and 59 %; two additional treatments controlled for the effects of anaesthesia and surgery. The angle of escape was unaffected by surgery. Maximum speed and minimum escape time were both significantly impaired by the high-removal treatments, but showed no evidence of decline until 30 % of the tail (length or depth) was removed. These results suggest that the relatively deep tails in predator-induced tadpoles (approximately 10 % deeper than in no-predator tadpoles) do not improve performance in burst swimming. Thus, predator-induced tadpoles are less vulnerable to predation for reasons other than enhanced swimming performance.
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Soriani, O., F. le Foll, L. Galas, F. Roman, H. Vaudry et L. Cazin. « The ς-ligand (+)-pentazocine depresses M current and enhances calcium conductances in frog melanotrophs ». American Journal of Physiology-Endocrinology and Metabolism 277, no 1 (1 juillet 1999) : E73—E80. http://dx.doi.org/10.1152/ajpendo.1999.277.1.e73.
Texte intégralRésumé :
Gramicidin-perforated patch clamp experiments and microfluorimetric measurements were performed to study the ionic mechanisms involved in the ς-receptor-mediated stimulation of frog ( Rana ridibunda) pituitary melanotrophs. The ς-ligand (+)-pentazocine (50 μM) depressed a sustained outward K+ current. The kinetic properties of this K+component, investigated by analyzing tail currents, were reminiscent of those of the M current ( I M), with an activation threshold close to −60 mV, a −21-mV half-maximal activation potential, and two-component exponential deactivation kinetics at −90 mV. (+)-Pentazocine (20 μM) produced a 12-mV rightward shift of the activation curve and accelerated the deactivation rate of the tail current. It is also demonstrated that (+)-pentazocine (20 μM) reversibly increased both voltage-dependent calcium conductances and internal calcium level. Altogether, these results suggest that the ς-receptor-induced modulation of I M and calcium currents likely underlies the increase of intracellular [Ca2+].
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Schulte-Merker, S., M. Hammerschmidt, D. Beuchle, K. W. Cho, E. M. De Robertis et C. Nusslein-Volhard. « Expression of zebrafish goosecoid and no tail gene products in wild-type and mutant no tail embryos ». Development 120, no 4 (1 avril 1994) : 843–52. http://dx.doi.org/10.1242/dev.120.4.843.
Texte intégralRésumé :
goosecoid is an immediate early gene expressed at the dorsal blastoporal lip of the Xenopus gastrula. Microinjection experiments have suggested a direct role for goosecoid in organizing the dorsoventral axis of the frog embryo. Here we characterize the zebrafish homologue of goosecoid (gsc) and compare its expression to that of Brachyury or no tail (ntl), another immediate early gene required in developing mesoderm. We show that gsc exhibits two independent phases of expression: an early one in cells anterior to the presumptive notochord, but not in cells of the notochord itself, and a later one in neural crest derivatives in the larval head. Zygotic gsc transcripts are detected soon after the midblastula transition, and at the blastula stage form a gradient with a maximum at the dorsal side. Use of gsc as a dorsal marker allowed us to demonstrate that ntl expression is initially activated at the dorsal side of the blastula. At this early stage, gsc and ntl show overlapping domains of expression and are co-expressed in cells at the dorsal midline of the early gastrula. However, gsc- and ntl-expressing cells become separated in the course of gastrulation, with gsc being expressed in the axial hypoblast (prechordal plate) anterior to the ntl-expressing presumptive notochord cells. Studies with mutant embryos suggest that gsc is independent of ntl function in vivo.
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Zamora-Camacho, Francisco Javier, Susana Cortés-Manzaneque et Pedro Aragón. « Simulated predation pressure in Pelobates cultripes tadpoles modulates morphology at the metamorphic stage ». Current Zoology 65, no 6 (19 décembre 2018) : 651–56. http://dx.doi.org/10.1093/cz/zoy097.
Texte intégralRésumé :
Abstract Studies on the impacts of variation of biotic interactions at key life cycle stages are crucial to understand the interface between ecological and developmental processes. Predators exert a major impact on prey fitness. Although direct consumption entails the greatest effect, predators can affect prey by means of other mechanisms. For instance, injuries inflicted by failed predation attempts can jeopardize prey fitness, even beyond the short-term. In anuran tadpoles, failed predation typically results in partial tail loss, which is known to reduce swimming speed. However, the potential consequences of tadpole partial tail loss after metamorphosis remain understudied. Because tail materials could be important in conforming metamorph body, we assess the effects of tadpole partial tail loss on metamorph body size in Iberian spadefoot toads Pelobates cultripes. We clipped 55% tail length of pre-tail-resorption stage anesthetized tadpoles, and compared their body size as metamorphs with anesthetized and non-anesthetized non-tail-clipped controls. Also, we tested whether tail length correlated with metamorph body size of individuals of the control groups. Tail-clipped tadpoles produced smaller metamorphs than both controls (the bdy size of metamorphs from both controls was similar), which could incur costs in mid-term survival or time to first reproduction. This effect could be particularly important in areas with introduced predators, if autochthonous tadpoles lack defenses against them. Results suggest that materials resorbed from tadpole tail tissues might be reallocated into metamorph body, according to the negative effect of shorter tails in a correlational analysis, and clipped tails in an experimental test, on metamorph body size.
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Stolow, M. A., D. D. Bauzon, J. Li, T. Sedgwick, V. C. Liang, Q. A. Sang et Y. B. Shi. « Identification and characterization of a novel collagenase in Xenopus laevis : possible roles during frog development. » Molecular Biology of the Cell 7, no 10 (octobre 1996) : 1471–83. http://dx.doi.org/10.1091/mbc.7.10.1471.
Texte intégralRésumé :
Matrix metalloproteinases (MMPs) participate in extracellular matrix remodeling and degradation and have been implicated in playing important roles during organ development and pathological processes. Although it has been hypothesized for > 30 years that collagenase activities are responsible for collagen degradation during tadpole tail resorption, none of the previously cloned amphibian MMPs have been biochemically demonstrated to be collagenases. Here, we report a novel matrix metalloproteinase gene from metamorphosing Xenopus laevis tadpoles. In vitro biochemical studies demonstrate that this Xenopus enzyme is an interstitial collagenase and has an essentially identical enzymatic activity toward a collagen substrate as the human interstitial collagenase. Sequence comparison of this enzyme to other known MMPs suggests that the Xenopus collagenase is not a homologue of any known collagenases but instead represents a novel collagenase, Xenopus collagenase-4 (xCol4, MMP-18). Interestingly, during development, xCol4 is highly expressed only transiently in whole animals, at approximately the time when tadpole feeding begins, suggesting a role during the maturation of the digestive tract. More importantly, during metamorphosis, xCol4 is regulated in a tissue-dependent manner. High levels of its mRNA are present as the tadpole tail resorbs. Similarly, its expression is elevated during hindlimb morphogenesis and intestinal remodeling. In addition, when premetamorphic tadpoles are treated with thyroid hormone, the causative agent of metamorphosis, xCol4 expression is induced in the tail. These results suggest that xCol4 may facilitate larval tissue degeneration and adult organogenesis during amphibian metamorphosis.
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Argaez, Víctor, Israel Solano-Zavaleta et J. Jaime Zúñiga-Vega. « Another potential cost of tail autotomy : tail loss may result in high ectoparasite loads in Sceloporus lizards ». Amphibia-Reptilia 39, no 2 (2018) : 191–202. http://dx.doi.org/10.1163/15685381-17000156.
Texte intégralRésumé :
Abstract Tail autotomy is a common phenomenon in lizards that increases the chances of immediate survival during a predation event or agonistic encounter. However, despite short-term benefits, tail regeneration may also impose costs. Several studies have demonstrated that tail loss compromises other vital functions such as lipid storage, reproduction, and the immune system. Several lizard species are hosts of mites and ticks. Here we evaluated in three lizard species from the genus Sceloporus, whether individuals that have lost their tails and invested energy in tail regeneration are more susceptible to ectoparasites. Using a multimodel inference framework, we examined if tail loss and regeneration, as well as sex, body condition, and season (dry or rainy) predict ectoparasite load. Our results indicate that investing energy and resources in tail regeneration compromises defence against ectoparasites. These costs differed between sexes and among species. Overall, ectoparasite load increases during the rainy season and is on average higher in males. In S. grammicus, during the rainy season, males with regenerated tails and in poor body condition had more ectoparasites than males with intact tails in good body condition. In S. megalepidurus, we observed the same effect during the rainy season but in females rather than males. In S. torquatus, we found no effect of tail loss on ectoparasite load. We discuss the possibility that differences observed among species reflect differences in both species-specific physiological trade-offs and local environmental conditions.
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Tilney, L. G., D. J. DeRosier et M. S. Tilney. « How Listeria exploits host cell actin to form its own cytoskeleton. I. Formation of a tail and how that tail might be involved in movement. » Journal of Cell Biology 118, no 1 (1 juillet 1992) : 71–81. http://dx.doi.org/10.1083/jcb.118.1.71.
Texte intégralRésumé :
After Listeria is phagocytosed by a macrophage, it dissolves the phagosomal membrane and enters the cytoplasm. The Listeria then nucleates actin filaments from its surface. These actin filaments rearrange to form a tail with which the Listeria moves to the macrophage surface as a prelude to spreading. Since individual actin filaments appear to remain in their same positions in the tail in vitro after extraction with detergent, the component filaments must be cross-bridged together. From careful examination of the distribution of actin filaments attached to the surface of Listeria and in the tail, and the fact that during and immediately after division filaments are not nucleated from the new wall formed during septation, we show how a cloud of actin filaments becomes rearranged into a tail simply by the mechanics of growth. From lineage studies we can relate the length of the tail to the age of the surface of Listeria and make predictions as to the ratio of Listeria with varying tail lengths at a particular time after the initial infection. Since we know that division occurs about every 50 min, after 4 h we would predict that if we started with one Listeria in a macrophage, 16 bacteria would be found, two with long tails, two with medium tails, four with tiny tails, and eight with no tails or a ratio of 1:1:2:4. We measured the lengths of the tails on Listeria 4 h after infection in serial sections and confirmed this prediction. By decorating the actin filaments that make up the tail of Listeria with subfragment 1 of myosin we find (a) that the filaments are indeed short (maximally 0.3 microns in length); (b) that the filament length is approximately the same at the tip and the base of the tail; and (c) that the polarity of these filaments is inappropriate for myosin to be responsible or to facilitate movement through the cytoplasm, but the polarity insures that the bacterium will be located at the tip of a pseudopod, a location that is essential for spreading to an adjacent cell. Putting all this information together we can begin to unravel the problem of how the Listeria forms the cytoskeleton and what is the biological purpose of this tail. Two functions are apparent: movement and pseudopod formation.
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Wong, Woon Kong, Guobin Fan et Yong Zeng. « Capturing Tail Risks Beyond VaR ». Review of Pacific Basin Financial Markets and Policies 15, no 03 (septembre 2012) : 1250015. http://dx.doi.org/10.1142/s0219091512500154.
Texte intégralRésumé :
Since Value-at-Risk (VaR) disregards tail losses beyond the VaR boundary, the expected shortfall (ES), which measures the average loss when a VaR is exceeded, and the tail-risk-of-VaR (TR), which sums the sizes of tail losses, are used to investigate risks at the tails of distributions for major stock markets. As VaR exceptions are rare, we employ the saddlepoint or small sample asymptotic technique to backtest ES and TR. Because the two risk measures are complementary to each other and hence provide more powerful backtests, we are able to show that (a) the correct specification of distribution tail, rather than heteroscedastic process, plays a key role to accurate risk forecasts; and (b) it is best to model the tails separately from the central part of distribution using the Generalized Pareto Distribution (GPD). To sum up, we provide empirical evidence that financial markets behave differently during crises, and extreme risks cannot be modeled effectively under normal market conditions or based on a short data history.
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Hager, Emily R., et Hopi E. Hoekstra. « Tail Length Evolution in Deer Mice : Linking Morphology, Behavior, and Function ». Integrative and Comparative Biology 61, no 2 (19 avril 2021) : 385–97. http://dx.doi.org/10.1093/icb/icab030.
Texte intégralRésumé :
Abstract Determining how variation in morphology affects animal performance (and ultimately fitness) is key to understanding the complete process of evolutionary adaptation. Long tails have evolved many times in arboreal and semi-arboreal rodents; in deer mice, long tails have evolved repeatedly in populations occupying forested habitat even within a single species (Peromyscus maniculatus). Here, we use a combination of functional modeling, laboratory studies, and museum records to test hypotheses about the function of tail-length variation in deer mice. First, we use computational models, informed by museum records documenting natural variation in tail length, to test whether differences in tail morphology between forest and prairie subspecies can influence performance in behavioral contexts relevant for tail use. We find that the deer- mouse tail plays little role in statically adjusting center of mass or in correcting body pitch and yaw, but rather it can affect body roll during arboreal locomotion. In this context, we find that even intraspecific tail-length variation could result in substantial differences in how much body rotation results from equivalent tail motions (i.e., tail effectiveness), but the relationship between commonly-used metrics of tail-length variation and effectiveness is non-linear. We further test whether caudal vertebra length, number, and shape are associated with differences in how much the tail can bend to curve around narrow substrates (i.e., tail curvature) and find that, as predicted, the shape of the caudal vertebrae is associated with intervertebral bending angle across taxa. However, although forest and prairie mice typically differ in both the length and number of caudal vertebrae, we do not find evidence that this pattern is the result of a functional trade-off related to tail curvature. Together, these results highlight how even simple models can both generate and exclude hypotheses about the functional consequences of trait variation for organismal-level performance.
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Langkilde, Tracy, et Ross A. Alford. « The Tail Wags the Frog : Harmonic Radar Transponders Affect Movement Behavior in Litoria lesueuri ». Journal of Herpetology 36, no 4 (décembre 2002) : 711–15. http://dx.doi.org/10.1670/0022-1511(2002)036[0711:ttwtfh]2.0.co;2.
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Heinrichs, Arianne. « Separating head from tail ». Nature Reviews Molecular Cell Biology 5, no 9 (septembre 2004) : 678. http://dx.doi.org/10.1038/nrm1476.
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Goerg, Georg M. « The Lambert Way to Gaussianize Heavy-Tailed Data with the Inverse of Tukey’shTransformation as a Special Case ». Scientific World Journal 2015 (2015) : 1–16. http://dx.doi.org/10.1155/2015/909231.
Texte intégralRésumé :
I present a parametric, bijective transformation to generate heavy tail versions of arbitrary random variables. The tail behavior of thisheavy tail Lambert W × FXrandom variable depends on a tail parameterδ≥0: forδ=0,Y≡X, forδ>0 Yhas heavier tails thanX. ForXbeing Gaussian it reduces to Tukey’shdistribution. The Lambert W function provides an explicit inverse transformation, which can thus remove heavy tails from observed data. It also provides closed-form expressions for the cumulative distribution (cdf) and probability density function (pdf). As a special case, these yield analytic expression for Tukey’shpdf and cdf. Parameters can be estimated by maximum likelihood and applications to S&P 500 log-returns demonstrate the usefulness of the presented methodology. The R packageLambertWimplements most of the introduced methodology and is publicly available onCRAN.
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Scadding, Steven R. « Vitamin A inhibits amphibian tail regeneration ». Canadian Journal of Zoology 65, no 2 (1 février 1987) : 457–59. http://dx.doi.org/10.1139/z87-070.
Texte intégralRésumé :
The objective of this investigation was to determine what effect vitamin A had on tail regeneration in Notophthalmus viridescens adults, in Ambystoma mexicanum larvae, and in Xenopus laevis tadpoles. Notophthalmus viridescens and Ambystoma mexicanum had their tails amputated and then were treated with retinol palmitate by immersion in concentrations known to cause proximodistal duplications in regenerating limbs. Xenopus laevis tadpoles had their tails amputated and then were treated with either retinol palmitate by immersion, or with retinoic acid administered by implantation of silastin blocks containing retinoic acid. The results ranged from no effect at all at the lower dose levels used, to complete inhibition of tail regeneration at higher dose levels. The degree of inhibition of tail regeneration appeared to be dose dependent. In no case were any duplicated or accessory structures formed analogous to those observed in regenerating limbs. This result suggests that the morphogenetic processes involved in tail regeneration are at least in some ways different from those occurring in limbs, where a similar vitamin A treatment would cause proximodistal duplication or production of accessory limb structures.
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Lim, Jaechul, Dongwan Kim, Young-suk Lee, Minju Ha, Mihye Lee, Jinah Yeo, Hyeshik Chang, Jaewon Song, Kwangseog Ahn et V. Narry Kim. « Mixed tailing by TENT4A and TENT4B shields mRNA from rapid deadenylation ». Science 361, no 6403 (19 juillet 2018) : 701–4. http://dx.doi.org/10.1126/science.aam5794.
Texte intégralRésumé :
RNA tails play integral roles in the regulation of messenger RNA (mRNA) translation and decay. Guanylation of the poly(A) tail was discovered recently, yet the enzymology and function remain obscure. Here we identify TENT4A (PAPD7) and TENT4B (PAPD5) as the enzymes responsible for mRNA guanylation. Purified TENT4 proteins generate a mixed poly(A) tail with intermittent non-adenosine residues, the most common of which is guanosine. A single guanosine residue is sufficient to impede the deadenylase CCR4-NOT complex, which trims the tail and exposes guanosine at the 3′ end. Consistently, depletion of TENT4A and TENT4B leads to a decrease in mRNA half-life and abundance in cells. Thus, TENT4A and TENT4B produce a mixed tail that shields mRNA from rapid deadenylation. Our study unveils the role of mixed tailing and expands the complexity of posttranscriptional gene regulation.
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Griffing, Aaron H., Thomas J. Sanger, Lilian Epperlein, Aaron M. Bauer, Anthony Cobos, Timothy E. Higham, Emily Naylor et Tony Gamble. « And thereby hangs a tail : morphology, developmental patterns and biomechanics of the adhesive tails of crested geckos ( Correlophus ciliatus ) ». Proceedings of the Royal Society B : Biological Sciences 288, no 1953 (16 juin 2021) : 20210650. http://dx.doi.org/10.1098/rspb.2021.0650.
Texte intégralRésumé :
Among the most specialized integumentary outgrowths in amniotes are the adhesive, scale-like scansors and lamellae on the digits of anoles and geckos. Less well-known are adhesive tail pads exhibited by 21 gecko genera. While described over 120 years ago, no studies have quantified their possible adhesive function or described their embryonic development. Here, we characterize adult and embryonic morphology and adhesive performance of crested gecko ( Correlophus ciliatus ) tail pads. Additionally, we use embryonic data to test whether tail pads are serial homologues to toe pads. External morphology and histology of C . ciliatus tail pads are largely similar to tail pads of closely related geckos. Functionally, C . ciliatus tail pads exhibit impressive adhesive ability, hypothetically capable of holding up to five times their own mass. Tail pads develop at approximately the same time during embryogenesis as toe pads. Further, tail pads exhibit similar developmental patterns to toe pads, which are markedly different from non-adhesive gecko toes and tails. Our data provide support for the serial homology of adhesive tail pads with toe pads.
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Kamata, Tetsuji, Makoto Handa, Yasuo Ikeda et Sadakazu Aiso. « Dissociation of the Extracellular α-Tail/β-Tail Interface Interaction Activates αIIbβ3 Integrin. » Blood 108, no 11 (16 novembre 2006) : 213. http://dx.doi.org/10.1182/blood.v108.11.213.213.
Texte intégralRésumé :
Abstract It is postulated that integrins undergo structural rearrangement from the low affinity bent conformer to the high affinity extended conformer upon activation. In inside-out signaling, the binding of talin to β cytoplasmic tail has been shown to activate integrin by disrupting the endogenous α/β cytoplasmic tail interaction that constrains integrin in low affinity state. How this intracellular event triggers structural rearrangement in the extracellular part of the integrin has not been elucidated. In integrin bent conformer, β-tail not only makes interface with β-head, but also makes large interface with α-tail. We previously reported that the membrane-proximal α-tail/β-tail interface interaction regulates integrin activation, and that stabilization of this interface completely blocks the propagation of inside-out signaling. From these results, we hypothesized that dissociation of the α-tail/β-tail following the dissociation of the α/β cytoplasmic tails triggers disruption of the β-head/β-tail interaction that constrains integrin in the bent state, thus activates integrin in inside-out signaling. Here we report that dissociation of the extracellular α-tail/β-tail actually activates αIIbβ3 integrin. To induce dissociation of the tails, we introduced N-linked glycosylation site (N-X-T/S) in αIIb amino acid residue Met-660 (M660NRT) which is located at the calf-1/EGF-3 interface that compose part of the α-tail/β-tail interface. When expressed in CHO cells, the mutant αIIbβ3 constitutively bound fibrinogen. Introduction of any sequences other than N-X-T/S in this site failed to activate αIIbβ3, suggesting this activation depends on the binding of a bulky N-glycan to the site. This activation was completely abolished when the β-head/β-tail interface was stabilized. Notably, stabilization of the membrane-proximal calf-2/EGF4-βTD interface with a disulfide bridge significantly inhibited activation induced by calf-1/EGF-3 dissociation, while it did not have any effect on fully extended αIIbβ3. These results suggest that disruption of the membrane-proximal α-tail/β-tail interface rather than the dissociation of the membrane-distal calf-1/EGF-3 interface is critical for initiating the structural rearrangement. Next, we examined whether disruption of the β-head/β-tail interface activates αIIbβ3 by introducing N-linked glycosylation site in β3 amino acid residue Gly-382 or in Thr-564 that are located at the β-head/β-tail interface. The resulting G382NLT and T564N mutants constitutively bound fibrinogen. This activation was completely abolished when αIIbβ3 was constrained in the bent conformer. Different from the M660NRT, this activation was not inhibited by stabilizing the calf-2/EGF4-βTD interface. In summary, these results suggest, 1) that disruption of the β-head/β-tail interface is required for the α-tail/β-tail dissociation to activate αIIbβ3, 2) that αIIbβ3 has to be able to extend for the disruption of the β-head/β-tail interface to activate αIIbβ3, 3) dissociation of the α-tail/β-tail is not required for activation, once β-head/β-tail interface is disrupted or αIIbβ3 is fully extended. Taken together, these results are consistent with our hypothesis and indicate that the α-tail/β-tail interface interaction is the key regulator of integrin activation in inside-out signaling.
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Koca, Yücel, Nazan Üzüm, Mehmet Turgut, Süleyman Kaplan, Murat Rağbetli, Emrah Soylu, Kurtuluş Olgun, Kubilay Metin, Elif Beytaş et Aziz Avcı. « Effects of Ca2+ channel blocker verapamil on tissue regeneration in a lizard tail autotomy model : a biochemical and histological study ». Amphibia-Reptilia 28, no 1 (2007) : 7–15. http://dx.doi.org/10.1163/156853807779798992.
Texte intégralRésumé :
AbstractCa2+ ions have been reported to augment the activities of many cell types including cellular proliferation and tissue regeneration. Moreover, it is well known that verapamil is a L-type voltage-gated Ca2+ antagonist with important clinical implications. To evaluate the role of Ca2+ ions in the regeneration of tail in lizards, verapamil was used in vivo to modulate the activity of intracellular Ca2+ in a lizard tail autotomy model. A total of 35 adult lizards were divided into three groups: lightness control group (n = 11), darkness group (n = 11) and verapamil treatment group (n = 13). The tails of adult lizards were amputated by pinching off the tail at the 15th segment from the vent to induce tail regeneration. The first two groups served as untreated constant lightness and darkness groups as controls, but the remaining group received intraperitoneally 1 mg/kg of verapamil. Following autotomy, the length of regenerating tails was measured at 10, 15, 20, 25, and 30 days post-amputation. At the end of the study, the regenerating tails from animals from each group were removed for collagen assay procedure and histological examination. We found that verapamil produced a reduction in the length of the regenerated tail compared to untreated lightness group and the percentage of tail replaced in verapamil treatment group was lower than those in lightness control group. Total collagen contents were found to be higher in lightness control group in comparison with darkness and verapamil treatment groups. Accordingly, a quantitative stereological evaluation showed a higher percentage of neural tissue and a lower percentage of connective tissue, as well as vascular tissue, in the cross-sections of the regenerated tails taken from Ca2+ channel blocker verapamil-treated lizards, as compared to other groups. In conclusion, our results suggest that verapamil influences a variety of processes including fibroblast collagen production, neurogenesis, and angiogenesis during tail regeneration in lizard, possibly due to inhibition of intracellular Ca2+ ion by verapamil.
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Kovacs, Erika, Rahul Das, Qi Wang, Timothy S. Collier, Aaron Cantor, Yongjian Huang, Kathryn Wong et al. « Analysis of the Role of the C-Terminal Tail in the Regulation of the Epidermal Growth Factor Receptor ». Molecular and Cellular Biology 35, no 17 (29 juin 2015) : 3083–102. http://dx.doi.org/10.1128/mcb.00248-15.
Texte intégralRésumé :
The ∼230-residue C-terminal tail of the epidermal growth factor receptor (EGFR) is phosphorylated upon activation. We examined whether this phosphorylation is affected by deletions within the tail and whether the two tails in the asymmetric active EGFR dimer are phosphorylated differently. We monitored autophosphorylation in cells using flow cytometry and found that the first ∼80 residues of the tail are inhibitory, as demonstrated previously. The entire ∼80-residue span is important for autoinhibition and needs to be released from both kinases that form the dimer. These results are interpreted in terms of crystal structures of the inactive kinase domain, including two new ones presented here. Deletions in the remaining portion of the tail do not affect autophosphorylation, except for a six-residue segment spanning Tyr 1086 that is critical for activation loop phosphorylation. Phosphorylation of the two tails in the dimer is asymmetric, with the activator tail being phosphorylated somewhat more strongly. Unexpectedly, we found that reconstitution of the transmembrane and cytoplasmic domains of EGFR in vesicles leads to a peculiar phenomenon in which kinase domains appear to be trapped between stacks of lipid bilayers. This artifactual trapping of kinases between membranes enhances an intrinsic functional asymmetry in the two tails in a dimer.
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Larrondo, C., H. Bustamante, E. Paredes et C. Gallo. « Long-term hyperalgesia and traumatic neuroma formation in tail-docked lambs ». Animal Welfare 28, no 4 (1 novembre 2019) : 443–54. http://dx.doi.org/10.7120/09627286.28.4.443.
Texte intégralRésumé :
This study aimed to determine if tail-docking induces long-term hyperalgesia, chronic pain and histopathological changes in tail stumps of tail-docked lambs. Fifty male lambs of 45 days of age were randomly allocated in two groups. One group of 25 lambs was tail-docked using a hot cautery iron and a second group of 25 lambs was subjected only to handling as a control group (undocked lambs). Prior to tail-docking and at intervals of 15, 30, 60 and 90 days after the procedure, infra-red thermography (IT) and mechanical nociceptive thresholds (MNTs) tests were carried out in both lambs' tails/stumps, and animals were weighed. In addition, the visual degree of inflammation of tail stumps was evaluated. Finally, animals were slaughtered in a commercial slaughterhouse and tail sections of ten lambs from each group were examined histopathologically. Tail-docking was associated with an inflammatory process according to IT and visual observation in tail stumps at 15 and 30 days post-docking. Tail-docked lambs had lower MNTs than undocked lambs at all evaluated times after tail-docking, indicating the presence of long-term hyperalgesia. Also, traumatic neuroma formation was found in tail stumps of 2/10 tail-docked lambs, and 6/10 presented neuromatous tissue development. It is concluded that tail-docking induces acute and chronic pain in lambs, initially through inflammation, and then via long-term hyperalgesia and traumatic neuroma formation. These long-term findings would have negative implications for the animal welfare of tail-docked lambs.
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Ghosh, Bikramaditya, et M. C. Krishna. « Power law in tails of bourse volatility – evidence from India ». Investment Management and Financial Innovations 16, no 1 (26 mars 2019) : 291–98. http://dx.doi.org/10.21511/imfi.16(1).2019.23.
Texte intégralRésumé :
Inverse cubic law has been an established Econophysics law. However, it has been only carried out on the distribution tails of the log returns of different asset classes (stocks, commodities, etc.). Financial Reynolds number, an Econophysics proxy for bourse volatility has been tested here with Hill estimator to find similar outcome. The Tail exponent or α ≈ 3, is found to be well outside the Levy regime (0 < α < 2). This confirms that asymptotic decay pattern for the cumulative distribution in fat tails following inverse cubic law. Hence, volatility like stock returns also follow inverse cubic law, thus stay way outside the Levy regime. This piece of work finds the volatility proxy (econophysical) to be following asymptotic decay with tail exponent or α ≈ 3, or, in simple terms, ‘inverse cubic law’. Risk (volatility proxy) and return (log returns) being two inseparable components of quantitative finance have been found to follow the similar law as well. Hence, inverse cubic law truly becomes universal in quantitative finance.
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Sánchez, Ricardo, et William F. Marzluff. « The Oligo(A) Tail on Histone mRNA Plays an Active Role in Translational Silencing of Histone mRNA during Xenopus Oogenesis ». Molecular and Cellular Biology 24, no 6 (15 mars 2004) : 2513–25. http://dx.doi.org/10.1128/mcb.24.6.2513-2525.2004.
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ABSTRACT Metazoan replication-dependent histone mRNAs end in a stem-loop sequence. The one known exception is the histone mRNA in amphibian oocytes, which has a short oligo(A) tail attached to the stem-loop sequence. Amphibian oocytes also contain two proteins that bind the 3′ end of histone mRNA: xSLBP1, the homologue of the mammalian SLBP, and xSLBP2, which is present only in oocytes. xSLBP2 is an inhibitor of histone mRNA translation, while xSLBP1 activates translation. The short A tail on histone mRNAs appears at stage II to III of oogenesis and is present on histone mRNAs throughout the rest of oogenesis. At oocyte maturation, the oligo(A) tail is removed and the xSLBP2 is degraded, resulting in the activation of translation of histone mRNA. Both SLBPs bind to the stem-loop with the oligo(A) tail with similar affinities. Reporter mRNAs ending in the stem-loop with or without the oligo(A) tail are translated equally well in a reticulocyte lysate, and their translation is stimulated by the presence of xSLBP1. In contrast, translation of the reporter mRNA with an oligo(A) tail is not activated in frog oocytes in response to the presence of xSLBP1. These results suggest that the oligo(A) tail is an active part of the translation repression mechanism that silences histone mRNA during oogenesis and that its removal is part of the mechanism that activates translation.
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Horemans, A. M. C., A. G. M. Tielens et S. G. Van Den Bergh. « The transition from an aerobic to an anaerobic energy metabolism in transforming Schistosoma mansoni cercariae occurs exclusively in the head ». Parasitology 102, no 2 (avril 1991) : 259–65. http://dx.doi.org/10.1017/s0031182000062570.
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SUMMARYIt has been shown that in intact cercariae of Schistosoma mansoni in water, both head and tail had an identical, aerobic energy metabolism. As long as the environment was water, glucose was mainly degraded to carbon dioxide by both head and tail whether or not these two were still connected to each other. Transfer of intact cercariae into a simple salt medium supplemented with glucose resulted in a very rapid transition towards a more anaerobic energy metabolism: the production of lactate and pyruvate increased, whereas the production of carbon dioxide remained more or less constant. A concomitant rise in temperature to 37°C was not essential for this biochemical transition, but made it more pronounced. Experiments on isolated cercarial bodies and tails in a transforming medium demonstrated that the tails oxidized glucose to carbon dioxide, whereas bodies produced mainly pyruvate and lactate. The results showed that the metabolic transition towards a more anaerobic energy metabolism occurred only in the head and not in the tail of the cercariae. Loss of the tail was shown not to be a pre-requisite for this transition, nor did it by itself trigger a metabolic switch in the resulting cercarial body.
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Vorobyov, Eduard I., Alexandr M. Skliarevskii, Vardan G. Elbakyan, Michihiro Takami, Hauyu Baobab Liu, Sheng-Yuan Liu et Eiji Akiyama. « The origin of tail-like structures around protoplanetary disks ». Astronomy & ; Astrophysics 635 (mars 2020) : A196. http://dx.doi.org/10.1051/0004-6361/201936990.
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Aims. We study the origin of tail-like structures recently detected around the disk of SU Aurigae and several FU Orionis-type stars. Methods. Dynamic protostellar disks featuring ejections of gaseous clumps and quiescent protoplanetary disks experiencing a close encounter with an intruder star were modeled using the numerical hydrodynamics code FEOSAD. Both the gas and dust dynamics were taken into account, including dust growth and mutual friction between the gas and dust components. Only plane-of-the-disk encounters were considered. Results. Ejected clumps produce a unique type of tail that is characterized by a bow-shock shape. Such tails originate from the supersonic motion of ejected clumps through the dense envelope that often surrounds young gravitationally unstable protostellar disks. The ejected clumps either sit at the head of the tail-like structure or disperse if their mass is insufficient to withstand the head wind of the envelope. On the other hand, close encounters with quiescent protoplanetary disks produce three types of the tail-like structure; we define these as pre-collisional, post-collisional, and spiral tails. These tails can in principle be distinguished from one another by particular features of the gas and dust flow in and around them. We find that the brown-dwarf-mass intruders do not capture circumintruder disks during the encounter, while the subsolar-mass intruders can acquire appreciable circumintruder disks with elevated dust-to-gas ratios, which can ease their observational detection. However, this is true only for prograde collisions; the retrograde intruders fail to collect appreciable amounts of gas or dust from the disk of the target. The mass of gas in the tail varies in the range 0.85–11.8 MJup, while the total mass of dust lies in the 1.75–30.1 M⊕ range, with the spiral tails featuring the highest masses. The predicted mass of dust in the model tail-like structures is therefore higher than what was inferred for similar structures in SU Aur, FU Ori, and Z CMa, making their observational detection feasible. Conclusions. Tail-like structures around protostellar and protoplanetary disks can be used to infer interesting phenomena such as clump ejection or close encounters. In particular, the bow-shock morphology of the tails could point to clump ejections as a possible formation mechanism. Further numerical and observational studies are needed to better understand the detectability and properties of the tails.