The International journal of developmental biology最新文献

Our understanding of avian sex determination and gonadal development is derived primarily from the studies in the chicken. Analysis of gynandromorphic chickens and experimental chimeras indicate that sexual phenotype is at least partly cell autonomous in the chicken, with sexually dimorphic gene expression occurring in different tissue and different stages. Gonadal sex differentiation is just one of the many manifestations of sexual phenotype. As in other birds, the chicken has a ZZ male: ZW female sex chromosome system, in which the male is the homogametic sex. Most evidence favours a Z chromosome dosage mechanism underling chicken sex determination, with little evidence of a role for the W chromosome. Indeed, the W appears to harbour a small number of genes that are un-related to sexual development, but have been retained because they are dosage sensitive factors. As global Z dosage compensation is absent in birds, Z-linked genes may direct sexual development in different tissues (males having on average 1.5 to 2 times the expression level of females). In the embryonic gonads, the Z-linked DMRT1 gene plays a key role in testis development. Beyond the gonads, other combinations of Z-linked genes may govern sexual development, together with a role for sex steroid hormones. Gonadal DMRT1 is thought to activate other players in testis development, namely SOX9 and AMH, and the recently identified HEMGN gene. DMRT1 also represses ovarian pathway genes, such as FOXL2 and CYP19A1. A lower level of DMRT1 expression in the female gonads is compatible with activation of the ovarian pathway. Some outstanding questions include how the key testis and ovary genes, DMRT1 and FOXL2, are regulated. In addition, confirmation of the central role of these genes awaits genome editing approaches.

After decades of research investment, techniques for the robust and efficient modification of the chicken genome are now with us. The biology of the chicken has provided many challenges, as have the methods by which transgenes can be readily, stably and functionally integrated into the genome. Now that these obstacles have been surmounted and the chicken has been 'updated' to a cutting-edge modern model organism, a future as a central and versatile model in developmental biology beckons. In this review, we describe recent advances in genetic modification of the chicken and some of the many transgenic models developed for the elucidation of the mechanisms of embryogenesis.

As one of the most economically important species and a unique model organism for biological and medical research, the chicken represents the first non-mammalian amniotic species to have its genome sequenced; and so far, the chicken reference genome represents the best assembled and annotated avian genome. Since the release of the first draft genome sequence, the chicken genome assembly has improved greatly in coverage, contiguity and accuracy owing to the continuous efforts made by the chicken genomics community to generate extensive new data using novel sequencing technologies. Transcriptome sequencing, especially the recent effort to characterise full-length transcripts in chicken tissues, has provided key insights into the complexity of structure and function of the chicken genome. In this article, we review the progress in chicken genome assembly and annotation, and recent advances in comparative genomics in birds. Limitations of current data and plans of research are also discussed.

Striated muscle is the most abundant tissue in the body of vertebrates and it forms, together with the skeleton, the locomotory system required both for movement and the creation of the specific body shape of a species. Research on the embryonic development of muscles has a long tradition both in classical embryology and in molecular developmental biology. While the gene networks regulating muscle development have been discovered mostly in the mouse through genetics, our knowledge on cell lineages, muscle morphogenesis and tissue interactions regulating their formation is to a large extent based on the use of the avian model. This review highlights present knowledge of the development of skeletal muscle in vertebrate embryos. Special focus will be placed on the contributions from chicken and quail embryo model systems.

The field of hematopoietic and vascular developmental research owes its origin to the chick embryo. Many key concepts, such as the hematopoietic stem cell, hemangioblast and hemogenic endothelium, were first proposed in this model organism. Genetically tractable models have gradually replaced the chick in the past two decades. However, advances in comparative genomics, transcriptomics and promoteromics promise a re-emergence of the chick embryo as a powerful model for hematopoietic/vascular research. This review summarizes the current status of our understanding of early blood/vascular development in the chick, focusing primarily on the processes of primitive hematopoiesis and early vascular network formation in the extraembryonic and lateral plate mesoderm territories. Emphasis is given to ontological and molecular association between the blood and endothelial cells and to the evolutionary relationship between the hemangioblasts, common precursors for the blood and endothelial lineages, and the coelomic epithelial lining cells. Links between early blood/vascular development and later definitive hematopoiesis are also discussed. Finally, potential applications of the chick model for comparative and omics-level studies of the blood/vascular system are highlighted.

While the external vertebrate body plan appears bilaterally symmetrical with respect to anterior-posterior and dorsal-ventral axes, the internal organs are arranged with a striking and invariant left-right asymmetry. This laterality is important for normal body function, as alterations manifest as numerous human birth defect syndromes. The left-right axis is set up very early during embryogenesis by an initial and still poorly understood break in bilateral symmetry, followed by a cascade of molecular events that was discovered 20 years ago in the chick embryo model. This gene regulatory network leads to activation of the pitx2 gene on the left side of the embryo which ultimately establishes asymmetric organogenesis of the heart, gut, brain, and other organs. In this review, we highlight the crucial contributions of the avian model to the discovery of the differential transcriptional cascades operating on the Left and Right sides, as well as to the physiological events operating upstream of asymmetric gene expression. The chick was not only instrumental in the discovery of mechanisms behind left-right patterning, but stands poised to facilitate inroads into the most fundamental aspects that link asymmetry to the rest of evolutionary developmental biology.

Pluripotency defines the ability of a cell to self-renew and to differentiate into all embryonic lineages both in vitro and in vivo. This definition was first established mainly with the mouse model and the establishment of mouse embryonic stem cells (ESCs) in the 1980's and extended later on to other species including non-human primates and humans. Similarly, chicken ESCs were derived and established in vitro from pregastrulating embryos leading to cells with unique properties at molecular, epigenetic and developmental levels. By comparing the properties of murine, mammalian and avian ESCs and of the more recently discovered induced pluripotential stem (iPS)-derived cells generated in all of these species, avian specificities start to emerge including specific molecular genes, epigenetic mark profiles and original developmental properties. Here, we present common, but also avian-specific elements that contribute to defining avian pluripotency.

During embryogenesis, different tissues develop coordinately, and this coordination is often in harmony with body growth. Recent studies allow us to understand how this harmonious regulation is achieved at the levels of inter-cellular, inter-tissue, and tissue-body relationships. Here, we present an overview of recently revealed mechanisms by which axial growth (tail growth) drives a variety of morphogenetic events, with a focus on the coordinated progression between Wolffian (nephric) duct elongation and somitogenesis. We also discuss how we can relate this coordination to the events occurring during limb bud outgrowth, since the limb buds and tail bud are appendage anlagen acquired during vertebrate evolution, both of which undergo massive elongation/outgrowth.

The chick embryo has provided a prominent model system for the study of segmental patterning in the nervous system. During early development, motor and sensory axon growth cones traverse the anterior/rostral half of each somite, so avoiding the developing vertebral components and ensuring separation of spinal nerves from vertebral bones. A glycoprotein expressed on the surface of posterior half-somite cells confines growth cones to the anterior half-somites by a contact repulsive mechanism. Hindbrain segmentation is also a conspicuous feature of chick brain development. We review how its contemporary analysis was initiated in the chick embryo, and the advantages the chick system continues to provide in its detailed elucidation at both molecular and neural circuit levels.

Avian brain organization or brain Bauplan is identical with that of vertebrates in general. This essay visits avian studies that contained advances or discussions about brain organization, trying to explain critically what they contributed. In order to start from a specific background, the new prevailing paradigm as regards brain organization, the prosomeric model, is presented first. Next a brief historic survey is made of how ideas on this topic evolved from the start of modern neuromorphology at the end of the 19th century. Longitudinal zonal organization with or without transverse segmentation (neuromeres) was the first overall concept applied to the brain. The idea of neuromeric structure later decayed in favour of a columnar model. This emphasized functional correlations rather than causal developmental content, assimilating forebrain functions to hindbrain ones. Though it became prevalent in the post-world-war period of neuroscience, in the last decades of the 20th century advances in molecular biology allowed developmental genes to be mapped, and it became evident that gene expression patterns support the old neuromeric model rather than the columnar one. This was also corroborated by modern experimental approaches (fate-mapping and analysis of patterning).