Academic literature on the topic 'Chick embryo - Embryology'

Abstract Background: In medical education, learning happens by variety of perceptions. In basic science Anatomy, visualization of real structures gives rich learning experience. This type seems deficient in human embryology, that too in the early phases. Aim: With the basic concept of'ontogeny repeats phylogeny', for the enrichment of learning early embryology, chick embryos have been used. Materials and methods: 30 commercially available chicken eggs and 30 Gallus domesticus [country chicken] eggs collected from nearby villages were hatched for embryos to whole mount, fix and stain. Results: Successful hatching rates were more in favour of Gallus domesticus eggs [76%] compared to others [26%] Conclusion: This experiment guides the easiest and simplest possible ways to successfully establish the learning module for early embryology in departmental setup using Gallus domesticus eggs. Observation of brain swellings, heart swelling optic vesicle, nasal pit, pharyngeal clefts, neural tube, somites and limb buds, vitelline vessels provide valuable learning experience by direct interaction with the real environment. This bridges the gap of seeing what is not usually observed and strengthens educational embryology

The formal teaching of developmental biology in India began in the late nineteen-fifties at the Department of Zoology of the University of Poona. This was due to the efforts of Leela Mulherkar, who on her return from C.H. Waddington’s laboratory in Edinburgh, took up the teaching of embryology at the Master’s level. Mulherkar began using locally available material to teach how animals develop. They included the embryos of chicken, frog, garden lizard and molluscs, as well as organisms such as hydra and sponges. Her teaching was supported by an active research laboratory that used all these systems to address a variety of questions in embryology and teratology. She used chick embryo explants cultured in vitro extensively in her work. Teaching and research in embryology at the master’s and doctoral levels at Poona University subsequently led, in 1977, to the establishment of the Indian Society of Developmental Biologists (InSDB), which is among the most active scientific societies in India.

The early stages of development of the chick embryo, leading to primitive streak formation (the start of gastrulation), have received renewed attention recently, especially for studies of the mechanisms of large-scale cell movements and those that position the primitive streak in the radial blastodisc. Over the long history of chick embryology, the terminology used to define different regions has been changing, making it difficult to relate studies to each other. To resolve this objectively requires precise definitions of the regions based on anatomical and functional criteria, along with a systematic molecular map that can be compared directly to the functional anatomy. Here, we undertake these tasks. We describe the characteristic cell morphologies (using scanning electron microscopy and immunocytochemistry for cell polarity markers) in different regions and at successive stages. RNAseq was performed for 12 regions of the blastodisc, from which a set of putative regional markers was selected. These were studied in detail by in situ hybridization. Together this provides a comprehensive resource allowing the community to define the regions unambiguously and objectively. In addition to helping with future experimental design and interpretation, this resource will also be useful for evolutionary comparisons between different vertebrate species.

The embryonic source and chemical nature of those factor/s directing the in vivo differentiation of melanocytes from crest cells are as yet unknown. To begin to address this issue, it is important to establish exactly when and where these signa/s first exert their effects. Therefore, in the present study, overtly differentiated melanocytes containing melanin were quantitated in developing Black Australorp X New Hampshire Red chick embryos. In contrast to previous studies, it was found that embryos synthesize melanin from as early as Day 5 of development, and that at this stage, the melanocytes are predominantly dermally located. Between 5 and 8 days, the numbers of both dermal and epidermal melanocytes increase, after which the dermal melanocyte population declines rapidly while the number of epidermal melanocytes continues to increase. These findings suggest that premelanocytes do not have to be epidermally located to initiate terminal differentiation and implicate the dermis as a possible source of melanocyte inducing factor/s. The next step was to examine stages of development prior to the onset of pigment production. For this reason, tyrosinase was purified for use as antigen in the production of a polyclonal antibody. The antibody was tested for specificity by western blotting, - immunocytochemistry and immunoinhibition procedures. Lack of specificity was demonstrated, rendering it unsuitable as an antibody marker for early melanocytes. Fowl melanocytes are thought to differentiate into either eumelanosome- or pheomelanosome synthesizing cells. To test the validity of this concept, embryonic skin of the red/black cross breed were screened for possible mixed type melanocytes by electron microscopy. The melanocytes contained melanosomes with a matrix of irregularly arranged filaments amongst typical eumelanogenic melanosomes. This suggests that these chick melanocytes may synthesize both eumelanosomes and pheomelanosomes in single cells. In a further study on pure breeding New Hampshire Reds, it was found that the melanocytes contained a mixture of typical and less typical pheomelanosomes. Outer membrane indentations in the latter melanosome type suggest that tyrosinase may enter these pheomelanosomes by a mechanism related to that proposed for the melanosomes of goldfish.

Body axis elongation is a hallmark of the vertebrate embryo, which also comprises the morphogenesis of the caudal neural tube (NT). The contribution of bipotential neuromesodermal progenitors (NMPs) to the cranio-caudal elongation of the embryo is beginning to be understood. However, the signalling pathways and tissue remodelling events required for shaping the caudal NT from NMPs remain largely unknown, even though the failure in this process generates caudal neural tube defects (NTDs). The caudal NT in amniote embryos forms by a process termed secondary neurulation (SN). SN shapes a secondary neural tube (SNT) through the lineage restriction and the mesenchymal-to-epithelial transition (MET) of NMPs into neural progenitor cells (NPCs), and the concomitant opening of a lumen de novo in the centre of the tissue. In human embryos, the development of the lumbar, sacral, coccygeal and equinal cord largely involves SN. The limited availability of human tissue to perform histological analyses at different developmental stages reinforces the need to use animal models to understand the events shaping the SNT, particularly since NTDs rank among the most common categories of birth defects, affecting 1 in every 1000 established pregnancies worldwide. Here, we combine the genetic manipulation of the chick embryo with an in vivo imaging technique to decipher the cellular events driving SNT formation and to demonstrate that TGF-b/SMAD3 signalling is required for proper SN, since its inhibition results in NTDs with multiple lumens. Our analysis demonstrates that the lineage restriction and the MET of Sox2+ T/Bra+ mesenchymal NMPs into Sox2+ T/Bra- epithelial neural progenitor cells (NPCs) are independent of SMAD3 activity. In the developing SNT, both the neural restriction and the MET tightly associate to the growing basement membrane (BM), which assembles in a dorso-ventral fashion. Hence, the first cells to adopt a neural identity and to undergo MET are those contacting the BM, located in the dorsal periphery of the medullary cord. On the contrary, centrally located cells remain mesenchymal, even to the very end of the process. It is between these two cell populations that small cavities of varied size and shape form, always at a one-cell distance from the BM, being SMAD3 also dispensable for lumen initiation. We found that the resolution of a single, centrally positioned continuous lumen in the SNT takes place through the intercalation of central cells, rather than through their programmed cell death. Indeed, results show an important novel activity for TGF-b/SMAD3 in the intercalation of central cells during lumen resolution. Notably, cell intercalation is always preceded by a cell division, either a symmetric II, which generates two intercalating daughter cells, or an asymmetric IC, which generates one intercalating and one central daughter cell. These two modes of division associate to different cranio-caudal levels, with II occurring cranially to IC. In addition, a third mode of division, the symmetric CC division, occurs in the caudal tail bud in order to generate two central mesenchymal NMPs and to expand the progenitor pool driving body axis elongation. Finally, we found lengthened primary cilia in sh-SMAD3 electroporated NPCs, a ciliopathy that might compromise the sensory functions of this organelle and ultimately contribute to the failure in central cell intercalation. Altogether, here we describe the cellular events driving SNT formation in the chick embryo and found a TGF-b/SMAD3-associated NTD. We anticipate our findings to be relevant to understand human SN and the embryonic origin of closed NTDs.
El alargamiento del eje del cuerpo es un sello distintivo del embrión de vertebrados. Los progenitores neuro-mesodérmicos (NMPs) llevan a cabo este proceso, incluyendo la morfogénesis del tubo neural caudal. En amniotas, éste se forma por el proceso conocido como neurulación secundaria (SN). El papel de los NMPs en el alargamiento del eje cráneo-caudal se conoce en mayor medida. Sin embargo, las vías de señalización y los eventos celulares que conforman el tubo neural secundario (SNT) se mantienen ampliamente desconocidos, aun cuando fallos en la SN producen defectos de tubo neural (NTDs). Aquí combinamos la manipulación genética del embrión de pollo con técnicas de imagen in vivo para descifrar los eventos celulares que conducen la formación del SNT y demostrar también que la vía de señalización TGF-beta/SMAD3 juega un papel muy importante en este proceso. Así, si ésta es inhibida durante el desarrollo del SNT se generan NTDs caracterizados por la presencia de múltiples lúmenes. Nuestro análisis demuestra que los eventos iniciales de la SN como la restricción de los NMPs en células progenitoras neurales (NPCs) y la subsecuente transición mesénquima-epitelio (MET) son independientes de la actividad de TGF-beta/SMAD3. No obstante, la resolución de un único lumen central, posible gracias a la intercalación de las células centrales, requiere la actividad de TGF-beta/SMAD3. Por todo ello, creemos que los hallazgos aquí presentados son relevantes para entender el proceso de SN en humano y así desentrañar el origen embrionario de los NTDs.

The causal and temporal aspects of blood tissue specification in the chick embryo were investigated in this study. The main focus was on the role of basic fibroblast growth factor (bFGF) in the determination of the erythropoietic tissue, particularly in context with its representation as a non-axial mesodermal derivative which arises in the posterior domain of the chick embryo. The initial strategy employed in this study was the use of agents that are known to block the activity of bFGF, and to determine their effects on erythropoiesis. Treatment of unincubated chick embryo explants with heparin, which binds specifically to the FGF family, was found to inhibit primitive streak formation and erythropoiesis, and also inhibited the formation of other mesodermal tissues. These initial findings suggested that one or more growth factors had become bound to the heparin, and that their activity is important for the specification of primitive streak formation and mesodermal patteming. The development of the erythropoietic tissue was assayed by a cytochemical test for haemoglobin using 0dianisidine; and by histological examination for blood islands and red blood cells in serial sections of the embryos after 48 hours incubation. Microscopic examination of the embryos at the stages of gastrulation on the first day of incubation revealed that heparin caused holes to appear in the ventral layer; and although a primitive streak did not form, a middle layer of mesenchymal cells were seen to accumulate between the ectodermal and ventral "endodermal" layers. It was significant that heparin's inhibitory effect on erythropoiesis could be reversed after the addition of a recombinant bovine bFGF to the heparin-treated embryos. However, the exogenous bFGF did not neutralize the inhibitory effect of heparin on the primitive streak and other mesodermal derivatives (Chapter Two). The inhibition of erythropoiesis by heparin was also reversed by the addition of a mesodermal-inducing factor extracted from a Xenopus embryonic cell line, namely XTC. The XTC mesodermal-inducing factor (MIF), which belongs to the transforming growth factor-B family and is a homologue of activin, could also reverse the inhibitory effect of heparin on primitive streak formation; but no recognizable axial mesodermal structures subsequently developed. Of consequence, was that both bFGF and XTC-MIF blocked heparin's effect on the ventral layer, preventing the gaps forming. Therefore, it is suggestive that the VI development of an intact ventral layer is important for the determination of the erythropoietic sequence (Chapter Three). By taking a more specific approach using antisera to bFGF (anti-FGF) and the bFGF receptor (anti-FGFR) on whole embryo explants, it was found that anti-FGP and anti-FGFR were able to inhibit erythropoiesis, but not primitive streak formation. However, these antisera caused defects in the posterior region of the embryonic axis. These embryos not only lacked posterior blood tissue, but heart and somites were missing; whereas the anterior head structures were well formed. These results therefore suggest that bFGF signalling is important for the development of the posterior body plan, which includes erythropoiesis (Chapter Four). Further evidence for the role of bFGF in the determination of the blood mesodermal tissue line was reached in an in vitro bioassay. In this part of the investigation, specific pieces of the blastoderm, namely pieces dissected from the posterior marginal zone (PMZ) and inner core of the central disc (lCD) were able to form haemoglobin under particular conditions. The PMZ components were found to have the capacity to form haemoglobin when dissected from blastoderms of stages X to xm when cultured in serum-free medium. This commitment to form haemoglobin could be blocked by treatment with anti-FGP at stages X and XI, but not at the later stages of xn and XIII. The ICD components were found to have a commitment to form haemoglobin only if this component was dissected from embryos at stage XIT and XITI, but not before. These results suggest that a determinative event for the haemoglobin differentiative pathway occurs between stages XI and XII. It was also found that the stage X central disc component could be induced to form haemoglobin if a stage xm hypoblast was added to it in tissue recombination sandwich cultures, or if bFGF (75 - 150 ng/ml) was added to the medium. These results lend further support that bFGF plays an important role in the determination of erythropoiesis; and furthermore, suggest that the hypoblastic tissue is the source of this induction (Chapter Four). Finally, immunocytochemical labelling with a polyclonal antibody to bFGF has revealed that bFGF increases significantly from stage XI in cells within the developing hypoblast layer and in the middle mesodermal layer. These cells are located predominantly in the posterior domain of the embryo. This polarized distribution of bFGF with the high value of bFGF concentration in the posterior area, is presumably responsible for inducing the overlying epiblast to form the posterior horseshoe-shaped region from which blood tissue is seen to arise. An immunocytochemical analysis of the distribution of the FGF receptor was vu assessed, as an indicator of the possible competence of the cells to respond to the bFGF signal. The bFGF receptor was found to be expressed at stage XII in cells that appeared to be in register with those immunoreactive to the bFGF ligand; therefore suggesting an autocrine function. It was interesting that at stage Xli an intense immunostaining with the anti-FGFR developed in the nuclei of cells within the epiblast layer (Chapter Five). In conclusion, this study has demonstrated that the initial determination of the erythropoietic cell lineage in the chick is at the time when the hypoblast is in the process of forming beneath the epiblast, Le. between stages XI and XII. Furthermore, it was found that an induction by an FGF-like signal from the hypoblast layer (or middle mesodermal cells that may be closely associated with the hypoblast) induces "competent" cells (Le. FGFR-positive cells) in the epiblast to form blood tissue in the posterior domain of the chick embryo.
Thesis (Ph.D.)-University of Natal, 1994.

A Dissertation submitted to the Faculty of Science, University of Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. 2015.
Prdm1/Blimp1 is a transcription factor whose mechanism of action is mainly repression; however it has been identified as an activator in some cases. As a transcriptional repressor, it plays multiple roles during embryonic development, including neural crest specification. Prdm1 acts by repressing large sets of genes via sequence specific recruitment of co-repressors, many of which are epigenetic modifiers. Neural crest is a transient, migrating cell population that gives rise to a number of diverse cell lineages that form important structures in the vertebrate embryo. Examples of these include peripheral nervous system, melanocytes and cranial cartilage. Prdm1 is expressed during neural crest specification in Xenopus, zebrafish and lamprey. The expression of Prdm1 had not yet been investigated in the neural crest during chick embryonic development. The mechanism of Prdm1 action or the nature of possible binding partners that mediate its effects in the neural crest had not yet been addressed. Prdm1 binding partners are known to play important roles during embryonic development, yet in many cases no spatiotemporal expression analysis during early vertebrate development has been performed. Single and double in situ hybridization for Prdm1 and all the binding partners was performed to determine localization of mRNA during early stages of chick embryonic development. We report the expression patterns of Prdm1 and seven of its known or putative binding partners (Hdac1, Hdac2, Tle1, Tle3, G9a, Prmt5 and Lsd1) during early stages (HH4-HH10) of chicken embryogenesis. Prdm1 expression was observed in the neural plate border and pre-migratory neural crest during chick development. Six Prdm1 binding partners (except Tle1) are co- expressed with Prdm1 in the prospective neural plate border at HH4-HH6, and all seven show strong and specific expression in the neural plate border at HH7-HH8, suggesting all of them co-operate with Prdm1 during neural crest development in chick embryos. Future work will focus on protein interaction studies in order to directly demonstrate the association between Prdm1 and the binding partners it co-localizes with.