Academic literature on the topic 'Xenopus laevis – Metamorphosis'

Shortly after hatching, Xenopus laevis tadpoles fill their lungs with air. We examined the role played by early lung use in these organisms, since they are able to respire with both their lungs and their gills. We investigated the effect on X. laevis development when the larvae were prevented from inflating their lungs, and whether early lung use influenced the size of the lungs or the tadpole's ability to metamorphose. Tadpoles that were denied access to air had lungs one-half the size of those of controls. This difference in lung size was too large to be explained merely by a stretching of the lung due to inflation. The longer tadpoles were denied access to air, the longer they took to metamorphose, and their probability of completing metamorphosis diminished. One tadpole raised throughout its larval life without access to air successfully metamorphosed but had abnormal, solidified lungs and an enlarged heart. Collectively, these experiments demonstrate that early lung use in tadpoles is important in determining both ultimate lung size and the probability of successfully metamorphosing. Lung use during early larval development in X. laevis is not absolutely necessary for survival through metamorphosis, but its absence severely handicaps growth.

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.

A monoclonal antibody (EPI-1), raised against the supernatant of a homogenate of Xenopus laevis larvae at the tailbud stage (stage 36/37), interacts specifically with a 250 KD epidermal antigen of Xenopus. An immunocytochemical gold-labeling technique was used to investigate changes in antigen distribution during epidermal development of Xenopus laevis. Specific immunolabeling was initially detected over the endoplasmic reticulum in the outer epithelial cells of the late gastrula stage (stage 12.5). After the early neurula stage (stage 13), immunolabeling appeared over moderately electron-dense bodies (these bodies disappear after stage 29), and also over the apical cell surface and adjacent cytoplasm of all the outer epithelial cells. During metamorphosis, labeling decreased and disappeared after stage 62, as the superficial layer had peeled off. These data suggest that the antigen is useful as a marker of general differentiation in studies of epidermal development during the embryonic and larval stages of Xenopus laevis.

La plasticité du système nerveux central face aux contraintes environnementales ou morphologiques est un processus fondamental mis en place afin de permettre à l’animal de maintenir des comportements adaptés. Parce que le comportement locomoteur est essentiel à la survie de l'animal, les mécanismes neuronaux permettant sa genèse doivent s’adapter aux modifications morphologiques de l’organisme pendant son développement. Pour aborder cette question, nous avons développé un nouveau modèle expérimental pour lequel les modifications morphologiques au cours du développement sont extrêmes et impliquent des reconfigurations à long terme du système nerveux. L'amphibien Xenopus laevis lors de sa métamorphose est, en effet, un modèle pertinent pour étudier (par des approches comportementales, neuroanatomiques, électro-physiologiques et pharmacologiques), les mécanismes impliqués dans la réorganisation des réseaux neuronaux locomoteurs de la moelle épinière face à des modifications extrêmes du schéma corporel. En effet, pendant sa métamorphose, l'animal passe d'un mode de locomotion ondulatoire mettant en jeu sa musculature axiale, à un mode de locomotion appendiculaire grâce aux membres néo-formés. Il existe de plus des stades intermédiaires où les deux modes de locomotion coexistent et expriment des relations fonctionnelles variables. Nos expériences d’électrophysiologie extracellulaire nous ont permis de dégager la dynamique temporelle de l’émergence du réseau de neurones commandant la locomotion appendiculaire adulte et de ses relations fonctionnelles avec le réseau locomoteur commandant la nage larvaire lorsque ces deux réseaux coexistent. D’après les résultats présentés, il apparaît un changement de l’équilibre fonctionnel et des interactions entre les commandes locomotrices ondulatoire et appendiculaire, faisant des stades intermédiaires de la métamorphose les témoins privilégiés du passage de relais progressif entre les deux systèmes locomoteurs. Nos travaux ont également démontré que l’activité de chaque réseau ainsi que leurs relations fonctionnelles sont sujettes à modulation glutamatergique et aminergique destinées à adapter la locomotion aux besoins de l'animal. Nous montrons que certains modulateurs (tels que le glutamate, la sérotonine et la noradrénaline) exercent des effets opposés sur les réseaux locomoteurs larvaires et adultes, alors qu'à l'inverse, la dopamine conserve les mêmes propriétés modulatrices sur ces réseaux malgré les profonds bouleversements subis pendant le développement. Outre leur rôle modulateur, nos résultats suggèrent aussi un rôle des afférences aminergiques dans la maturation des réseaux locomoteurs et ouvrent de nombreuses interrogations quant aux mécanismes impliqués dans la plasticité des afférences neuromodulatrices elles-mêmes au cours de la métamorphose. L’apparition et la disparition de neurones sérotoninergiques intraspinaux concomitantes avec la croissance des membres postérieurs, et précédant la régression de l'appendice caudal laissent envisager un rôle de la sérotonine dans la maturation du réseau locomoteur appendiculaire ou dans la chronologie de la régression du réseau axial
Plasticity of the central nervous system is fundamental to an animal's capacity to adapt to continually changing biomechanical and environmental demands. Although the neuronal mechanisms underlying such essential behaviours as locomotion must adapt to an organism's morphological modifications during growth and development, the associated changes that occur in central nervous function remain poorly understood. To address this issue, we have developed a new experimental model - the amphibian Xenopus laevis during its metamorphosis - in which the extreme biomechanical modifications occurring during this critical period necessitate a correspondingly extensive and long-term reorganisation of locomotor neural circuitry within the animal's spinal cord. During metamorphosis, the locomotory strategy of Xenopus shifts from undulatory swimming involving axial tail-based movements, to appendicular propulsion that uses the newly formed limbs. At intermediate metamorphic stages, moreover, the two locomotor strategies coexist within the same animal as the secondary limb-based motor circuitry is progressively replaces the primary axial network as the limbs are added and the tail regresses. By making extracellular recordings of spontaneous "fictive" locomotor patterns generated by isolated brainstem/spinal cord preparations, we have charted the temporal dynamics of the emergence of the appendicular neuronal network and determined its functional relationship with larval axial locomotor circuitry through the metamorphic period. Our results have shown that the limb circuitry is initially present but not functional, functional but subordinate to the embryonic axial network, functionally independent from the axial network, and ultimately alone after axial circuitry disappears with tail resorption. Furthermore, the use of pharmacological approaches established that during the metamorphic transition, the coexisting spinal locomotory networks and their functional interactions are subject to glutamatergic and aminergic modulation in order to adapt locomotory performance to the immediate behavioural needs of the animal. Interestingly, the neuromodulators glutamate, serotonin and noradrenaline exert directly opposing influences on the larval and adult locomotor networks, while dopamine preserves a similar modulatory action on the two circuits in spite of their profound remodelling during metamorphic development. Finally, in addition to a short-term modulatory role, our immunocytochemical evidence suggested that descending aminergic systems may contribute to the long-term maturation of spinal locomotor circuitry during metamorphosis in parallel with their own developmental reconfiguration. Specifically, the appearance and disappearance of a population of intraspinal serotonergic neurons concomitant with hindlimb growth and preceding tail regression suggested a role of serotonin in the maturation of the appendicular locomotor network and/or in the chronology of axial network regression

Triclosan (TCS) and triclocarban (TCC) are antimicrobials found in U.S. surface waters. This dissertation assessed the effects of TCS and TCC on early development and investigated their potential to bioaccumulate using Xenopus laevis as a model. The effects of TCS on metamorphosis were also investigated. For 0-week tadpoles, LC50 values for TCS and TCC were 0.87 mg/L and 4.22 mg/L, respectively, and both compounds caused a significant stunting of growth. For 4-week tadpoles, the LC50 values for TCS and TCC were 0.22 mg/L and 0.066 mg/L; and for 8-week tadpoles, the LC50 values were 0.46 mg/L and 0.13 mg/L. Both compounds accumulated in Xenopus. For TCS, wet weight bioaccumulation factors (BAFs) for 0-, 4- and 8-week old tadpoles were 23.6x, 1350x and 143x, respectively. Lipid weight BAFs were 83.5x, 19792x and 8548x. For TCC, wet weight BAFs for 0-, 4- and 8-week old tadpoles were 23.4x, 1156x and 1310x. Lipid weight BAFs were 101x, 8639x and 20942x. For the time-to-metamorphosis study, TCS showed an increase in weight and snout-vent length in all treatments. Exposed tadpoles metamorphosed approximately 10 days sooner than control tadpoles. For the hind limb study, although there was no difference in weight, snout-vent length, or hind limb length, the highest treatment was more developed compared to the control. There were no differences in tail resorption rates between the treatments and controls. At relevant concentrations, neither TCS nor TCC were lethal to Xenopus prior to metamorphosis. Exposure to relatively high doses of both compounds resulted in stunted growth, which would most likely not be evident at lower concentrations. TCS and TCC accumulated in Xenopus, indicating that the compound has the potential to bioaccumulate through trophic levels. Although TCS may increase the rate of metamorphosis in terms of developmental stage, it did not disrupt thyroid function and metamorphosis in regards to limb development and tail resorption.

Au cours de la métamorphose, les amphibiens subissent une réorganisation complète de leur anatomie et de leur physiologie. Chez Xenopus laevis le système locomoteur est un des plus affecté au cours de cette phase développementale, l’animal passant d’une nage ondulatoire à une nage appendiculaire. Cette transformation du mode locomoteur implique une réorganisation du réseau locomoteur central. Dans une première étude, nous avons mis en évidence que les muscles axiaux s’activent de manière bilatéralement alternée chez le têtard alors que les muscles équivalents chez l’adulte s’activent de manière synchrone au cours de la nage. Nous avons montré que ce nouveau patron d’activation musculaire, accompagné d’une synchronisation avec les muscles appendiculaires extenseurs, reposent principalement sur la mise en place de nouvelles projections propriospinales lombo-thoraciques. Ces résultats suggèrent l’existence d’un contrôle postural proactif au cours de la locomotion, reposant directement sur le CPG des membres postérieurs. Dans une deuxième étude, nous nous sommes intéressés à l’influence d’un déséquilibre des afférences vestibulaires sur le développement du réseau locomoteur spinal au cours de la métamorphose. Pour cela nous avons réalisé une suppression unilatérale des organes vestibulaires avant ou après la métamorphose. Dans les deux cas, cette lésion aigue génère d’importants troubles locomoteurs et posturaux. Nous avons montré que la lésion chronique au cours de la métamorphose entraîne une modification ipsi-lésionnelle du développement du réseau locomoteur lombo-thoracique, de manière concomitante à une compensation comportementale. De façon intéressante, cette plasticité développementale ainsi que la compensation des troubles locomoteurs sont absentes chez les animaux lésés au stade adulte. Ces résultats suggèrent que les informations sensorielles sont un facteur déterminant pour le développement du réseau locomoteur spinal. Enfin, dans une troisième étude, nous avons analysé le développement du réseau locomoteur supra-spinal et en particulier les propriétés de déclenchement et de contrôle de la région locomotrice mésencéphalique (MLR). Nous avons mis en évidence l’existence fonctionnelle des deux noyaux de cette structure, le noyau pédonculopontin (PPN) et le noyau latérodorsal du tegmentum (LDT) tout au long de la métamorphose du xénope, ainsi qu’une fréquence d’activation optimale de 10-20 Hz pour le PPN
Throughout the course of metamorphosis, amphibians undergo a complete anatomical and physiological reorganization. In Xenopus laevis, the locomotor system is one of the most affected during this developmental phase where the animal passes from undulatory swimming to limb-based propulsion. This transformation implies a parallel reorganization of the central locomotor network. In an initial study we showed that axial muscles which are activated in bilateral alternation in tadpoles mature to dorsal muscles that are synchronously active during adult locomotion. We found that this new pattern, accompanied by coordination of dorsal and hindlimb muscle activities, is principally sustained by the development of new propriospinal lumbo-thoracic projections, suggesting proactive postural control coming from the hindlimb CPG during ongoing locomotion. In a second study, we examined the influence of disequilibrium in vestibular inputs on the metamorphic development of the spinal locomotor network. To induce this sensory asymmetry we performed unilateral removal of vestibular end organs either before or after metamorphosis. Acutely, in both cases, the lesion induced dramatic postural and locomotor changes. Chronically, the lesion altered the metamorphic development of the lumbo-thoracic network on the lesioned side, concomitantly with compensation for locomotor defects. Interestingly, animals lesioned after metamorphosis neither compensated nor expressed this developmental spinal plasticity. Altogether, these results suggest that descending sensory inputs are crucial cues for the development of the spinal locomotor network. Finally, we studied the metamorphic development of the supra-spinal network, focusing our attention on the locomotor triggering and control properties of the mesencephalic locomotor region (MLR). We showed that both subparts of this structure, the laterodorsal tegmentum (LDT) and the pedunculopontine (PPN) nuclei, are present and functional during the entire period of metamorphosis and that the PPN has an optimal activation frequency of 10-20 Hz

Les connexions de l'aire sensorielle octavolaterale du systeme nerveux central (aire primaire des fonctions acoustiques, vestibulaires et de la ligne laterale) ont ete tracees a l'aide de la peroxydase du raifort (hrp) chez trois amphibiens anoures au cours de leur developpement, le xenope, le discoglosse et la gastrotheque. Cette etude a permis de determiner les caracteristiques temps de latence au prelevement et vitesse de transport de la hrp dans le systeme nerveux central des anoures en developpement. En debut de metamorphose, le plan d'organisation des connexions de l'aire octavolaterale est similaire chez les trois anoures etudies. Il consiste en une connexion bilaterale de l'aire avec elle-meme et avec la formation reticulee et en une projection bilaterale vers l'olive superieure et vers le tegmentum: tores semicirculaires et region oculomotrice. Au cours de l'ontogenese, le contingent de connexions ipsilaterales tegmentales regresse chez le xenope et la gastrotheque et au dernier stade de la metamorphose, le plan d'organisation du systeme octavolateral correspond a celui etabli comme typique des anoures selon les donnees de la litterature. Cependant le discoglosse ne s'inscrit pas dans ce schema car l'ensemble des connexions tegmetales disparait a la fin de la metamorphose. La comparaison de l'evolution de la cytoarchitecture et des connexions du systeme octavolateral au cours de l'ontogenese chez les trois anoures etudies est discutee d'un point de vue phylogenetique et eco-ethologique

Xenopus laevis tadpoles were exposed for 48, 96 and 144 h during sexual differentiation to 1.8, 19 and 48 og/L atrazine. Following the exposure, tadpoles were microdissected for histological examination of the gonadal-kidney complex. The experimental tadpoles showed no significant difference in body weight, body length and in their development among the treatments. However, quantitative histological analysis of the gonads revealed a significant reduction of testicular volume, primary spermatogonial cell nests, and nursing cells in males as atrazine concentration and length of exposure increased. Females showed significant declines in primary oogonia cells and a significantly higher frequency of atresia with increasing atrazine concentration and length of exposure. The presence of a Wilms-like tumour was reported for the first time in tadpoles following exposure to atrazine. Qualitative histological analysis of the kidney showed a significant increase in the incidence of Renal Embryonal Adenosarcoma in all atrazine treated tadpoles. Females showed a significantly higher risk from developing tumours and tumour incidence as compared to males. These results suggests that the present non observable effect level (NOEL) for aquatic ecosystem of 20og/L atrazine should be reconsidered.

Thesis (M.S.)--University of Georgia, 2004.
Directed by Marsha C. Black. Includes articles submitted to Jorunal of toxicology and environmental health and Environmental toxicology and chemistry. Includes bibliographical references.

A Dissertation Submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg for the Degree of Master of Science March 1982
The effects of '5-FUdR and 5-BUdR on differentiation and metamorphosis in Xenopus lacyis tadpoles were studied. In particular, a detailed study was made of the effects of 5-fUdR on cellular patterning and tissue differentiation during hind’imb development. Xenopus ,laevis tadpoles grown in solutions of 5-FUdR and 5-BUdR demonstrated hindlimb deformities* which were analysed by staining for cartilage visibility. Furthermore a comparison of the uptake of exogenous radioactive thymidine in the presence and absence of 5-FUdR by ^ejropus 1aevis tadpoles showed that 5-FUdR depressed exogenous thymidine uptahe, A buoyant density gradient analysis of G-BUdR-substituted DHA was undertaken using the analytical ultraccntrifuge. The resulting ultraviolet absorption photographs showed bands heavy and noria&l DMA, A aodel is proposed to explain the patterning of the Xenopus 1aevis hindlinb in the presence or absence of 5-FUdR.

The objectives of this research were to observe the effects of specific contaminants on different amphibian species at various times of their life cycles, namely metamorphosis and fertilization. The effects of a non-ionic surfactant, Nonylphenol (NP), on Rana catesbeiana (bullfrog) tadpole metamorphic staging and tail resorption were examined, along with the effects of pH, osmolality and a divalent metal ion, Zinc (Zn²⁺), on Xenopus laevis (African clawed frog) sperm motility and kinematics. I hypothesized that 1) NP would have indirect sub-lethal effects on thyroid hormone function by disrupting metamorphosis in bullfrog tadpoles, and 2) aquatic parameters (pH, osmolality and Zn²⁺ concentration) would have significant effects on percent sperm motility, velocities and kinematics. This latter hypothesis was the basis for the development of the Amphibian Sperm Inhibition Toxicological Test (ASITT) method. To test the effect of NP on metamorphosis, there were 3 NP concentrations used (234, 468 and 936 ug/L) in both the presence and absence of 3,3',5-triiodothyronine (T₃), a well water control, a T₃ control and a solvent control for a total of 9 treatments with three replicates each. Tadpoles were exposed for 7 days whereupon tail length, width, and metamorphic staging was measured. NP had a significant effect on tail length and metamorphic staging in the absence of T₃, causing an increase in tail length and a decrease in limb development, respectively, with increasing NP concentrations. In the presence of T₃, increasing NP caused a significant reduction in cranial transformation. These results suggest an indirect inhibition of T₃ during tadpole metamorphosis. For the development of ASITT, first the effects of pH and osmolality on sperm motility had to be determined. The pH 7.0 and 56.625 mosmol/L treatments gave the highest percent motility and the control solution for ASITT was then developed using these solution parameters. Zn²⁺ was used for preliminary validation of ASITT method. It was added to the control solution in concentrations from 0 to 1,417 μg/L for 7 treatments each with 12 replicates. Increasing Zn²⁺ concentrations caused a significant decrease in percent total motile sperm and progressive sperm. Straight line velocity increased with increasing Zn²⁺ concentrations. These results suggest that Zn²⁺ is inhibiting the sperm at early stages of motility, possibly by preventing calcium influxes into the cell or inhibiting cellular respiration.