RESUMO
Scaffoldin, an S100 fused-type protein (SFTP) with high amino acid sequence similarity to the mammalian hair follicle protein trichohyalin, has been identified in reptiles and birds, but its functions are not yet fully understood. Here, we investigated the expression pattern of scaffoldin and cornulin, a related SFTP, in the developing beaks of birds. We determined the mRNA levels of both SFTPs by reverse transcription polymerase chain reaction (RT-PCR) in the beak and other ectodermal tissues of chicken (Gallus gallus) and quail (Coturnix japonica) embryos. Immunohistochemical staining was performed to localize scaffoldin in tissues. Scaffoldin and cornulin were expressed in the beak and, at lower levels, in other embryonic tissues of both chickens and quails. Immunohistochemistry revealed scaffoldin in the peridermal compartment of the egg tooth, a transitory cornified protuberance (caruncle) on the upper beak which breaks the eggshell during hatching. Furthermore, scaffoldin marked a multilayered peridermal structure on the lower beak. The results of this study suggest that scaffoldin plays an evolutionarily conserved role in the development of the avian beak with a particular function in the morphogenesis of the egg tooth.
Assuntos
Proteínas Aviárias/genética , Bico/metabolismo , Galinhas/genética , Coturnix/genética , Plumas/metabolismo , Casco e Garras/metabolismo , Animais , Proteínas Aviárias/metabolismo , Bico/citologia , Bico/embriologia , Evolução Biológica , Embrião de Galinha , Galinhas/crescimento & desenvolvimento , Galinhas/metabolismo , Sequência Conservada , Coturnix/embriologia , Coturnix/metabolismo , Embrião não Mamífero , Epiderme/embriologia , Epiderme/metabolismo , Plumas/citologia , Plumas/embriologia , Regulação da Expressão Gênica no Desenvolvimento , Casco e Garras/citologia , Casco e Garras/embriologia , Proteínas de Filamentos Intermediários/genética , Proteínas de Filamentos Intermediários/metabolismo , Queratinócitos/citologia , Queratinócitos/metabolismo , Mamíferos , Morfogênese/genética , Zigoto/crescimento & desenvolvimento , Zigoto/metabolismoRESUMO
Embryos from aquatic birds are the primary models for the study of flipper development. While some staging of early embryogenesis in duck have been studied, characterization of the stages of the entire embryonic development period in water birds has not been described. This study aimed to establish a comparison of complete morphological development staging for ducks (Anas platyrhynchos) and geese (Anser cygnoides) with the embryonic staging system by Hamburger and Hamilton (HH) for the chicken (Gallus gallus). Our results show that morphological development in the chicken, duck, and goose are similar in the early stages. The major differences occurred after stage 27 of embryonic development, where the beak shape in ducks and geese was wider and longer than in chickens. In addition, the second and third interdigital webs of the hind limb of the chicken were found to be degraded from stage 31, and eventually vanished at stage 35; however, they were retained in ducks and geese. Rapid physical development occurred in the mid-to-late stages in ducks and geese. To our best knowledge, this is the first description of complete embryonic development for the duck and goose. Establishment of an embryonic staging system for duck and goose provides new models for the study of waterfowl development.
Assuntos
Embrião de Galinha/embriologia , Patos/embriologia , Gansos/embriologia , Animais , Bico/embriologia , Embrião não Mamífero/embriologia , Desenvolvimento Embrionário , Membro Posterior/embriologiaRESUMO
For well over half of the 150 years since the discovery of the neural crest, the special ability of these cells to function as a source of species-specific pattern has been clearly recognized. Initially, this observation arose in association with chimeric transplant experiments among differentially pigmented amphibians, where the neural crest origin for melanocytes had been duly noted. Shortly thereafter, the role of cranial neural crest cells in transmitting species-specific information on size and shape to the pharyngeal arch skeleton as well as in regulating the timing of its differentiation became readily apparent. Since then, what has emerged is a deeper understanding of how the neural crest accomplishes such a presumably difficult mission, and this includes a more complete picture of the molecular and cellular programs whereby neural crest shapes the face of each species. This review covers studies on a broad range of vertebrates and describes neural-crest-mediated mechanisms that endow the craniofacial complex with species-specific pattern. A major focus is on experiments in quail and duck embryos that reveal a hierarchy of cell-autonomous and non-autonomous signaling interactions through which neural crest generates species-specific pattern in the craniofacial integument, skeleton, and musculature. By controlling size and shape throughout the development of these systems, the neural crest underlies the structural and functional integration of the craniofacial complex during evolution.
Assuntos
Padronização Corporal/fisiologia , Crista Neural/citologia , Crista Neural/fisiologia , Animais , Bico/embriologia , Osso e Ossos/embriologia , Região Branquial , Diferenciação Celular/fisiologia , Quimera/embriologia , Patos/embriologia , Face/embriologia , Regulação da Expressão Gênica no Desenvolvimento/fisiologia , Humanos , Crista Neural/embriologia , Codorniz/embriologia , Esqueleto/embriologia , Crânio/embriologia , Especificidade da EspécieRESUMO
The epithelial disintegration and the mesenchymal bridging are critical steps in the fusion of facial prominences during the upper lip development. These processes of epithelial-mesenchymal transition and programmed cell death are mainly influenced by Wnt signals. Axis inhibition protein2 (Axin2), a major component of the Wnt pathway, has been reported to be involved in lip development and cleft pathogenesis. We wanted to study the involvement of Axin2 in the lip development, especially during the epithelial disintegration of facial prominences. Our results show that Axin2 was expressed mainly in the epithelium of facial prominences and decreased when the prominences were about to contact each other between Hamburger-Hamilton stages 27 and 28 of chicken embryos. The epithelial integrity was destructed or kept intact by the local gain or loss of Axin2 expression, resulting in morphological changes in the facial processes and their skeletal derivatives including the maxilla, nasal, premaxilla bone, and their junctions without cleft formation. These changes were related to expression changes in nuclear ß-catenin, pGSK3ß, Slug, Smad3, E-cadherin, and p63. All these data indicate that Axin2 participates in the regulation of epithelial integrity and fusion by promoting epithelial disassociation, basement membrane breakdown, and seam loss during the fusion of facial prominences in lip development.
Assuntos
Proteínas Aviárias/genética , Proteína Axina/genética , Bico/embriologia , Galinhas/crescimento & desenvolvimento , Galinhas/genética , Regulação da Expressão Gênica no Desenvolvimento , Morfogênese , Animais , Bico/metabolismo , Morte Celular , Embrião de Galinha/citologia , Embrião de Galinha/metabolismo , Galinhas/metabolismoRESUMO
The toothless beak of modern birds was considered as an adaption for feeding ecology; however, several recent studies suggested that developmental factors are also responsible for the toothless beak. Neontological and palaeontological studies have progressively uncovered how birds evolved toothless beaks and suggested that the multiple occurrences of complete edentulism in non-avian dinosaurs were the result of selection for specialized diets. Although developmental biology and ecological factors are not mutually exclusive, the conventional hypothesis that ecological factors account for the toothless beak appears insufficient. A recent study on dinosaur incubation period using embryonic teeth posited that tooth formation rate limits developmental speed, constraining toothed dinosaur incubation to slow reptilian rates. We suggest that selection for tooth loss was a side effect of selection for fast embryo growth and thus shorter incubation. This observation would also explain the multiple occurrences of tooth loss and beaks in non-avian dinosaur taxa crownward of Tyrannosaurus Whereas our hypothesis is an observation without any experimental supports, more studies of gene regulation of tooth formation in embryos would allow testing for the trade-off between incubation period and tooth development.
Assuntos
Bico/embriologia , Evolução Biológica , Aves/embriologia , Dinossauros/embriologia , Animais , Fósseis , Filogenia , Dente/embriologiaAssuntos
Bico/anatomia & histologia , Evolução Biológica , Aves/anatomia & histologia , Aves/genética , Fator 8 de Crescimento de Fibroblasto/genética , Proteínas Hedgehog/genética , Animais , Bico/embriologia , Aves/embriologia , Osso e Ossos/anatomia & histologia , Osso e Ossos/embriologia , FósseisRESUMO
The avian beak is a key evolutionary innovation whose flexibility has permitted birds to diversify into a range of disparate ecological niches. We approached the problem of the mechanism behind this innovation using an approach bridging paleontology, comparative anatomy, and experimental developmental biology. First, we used fossil and extant data to show the beak is distinctive in consisting of fused premaxillae that are geometrically distinct from those of ancestral archosaurs. To elucidate underlying developmental mechanisms, we examined candidate gene expression domains in the embryonic face: the earlier frontonasal ectodermal zone (FEZ) and the later midfacial WNT-responsive region, in birds and several reptiles. This permitted the identification of an autapomorphic median gene expression region in Aves. To test the mechanism, we used inhibitors of both pathways to replicate in chicken the ancestral amniote expression. Altering the FEZ altered later WNT responsiveness to the ancestral pattern. Skeletal phenotypes from both types of experiments had premaxillae that clustered geometrically with ancestral fossil forms instead of beaked birds. The palatal region was also altered to a more ancestral phenotype. This is consistent with the fossil record and with the tight functional association of avian premaxillae and palate in forming a kinetic beak.
Assuntos
Bico/anatomia & histologia , Evolução Biológica , Aves/anatomia & histologia , Regulação da Expressão Gênica no Desenvolvimento , Palato/anatomia & histologia , Animais , Bico/embriologia , Aves/embriologia , Aves/genética , Embrião de Galinha , Galinhas , Fósseis/anatomia & histologia , Palato/embriologia , Fenótipo , Répteis/anatomia & histologia , Répteis/embriologia , Répteis/genéticaRESUMO
The standard model of evolutionary change of form, deriving from Darwin's theory via the Modern Synthesis, assumes a gradualistic reshaping of anatomical structures, with major changes only occurring by many cycles of natural selection for marginal adaptive advantage. This model, with its assertion that a single mechanism underlies both micro- and macroevolutionary change, contains an implicit notion of development which is only applicable in some cases. Here we compare the embryological processes that shape the vertebrate limb bud, the mammalian tooth and the avian beak. The implied notion of development in the standard evolutionary picture is met only in the case of the vertebrate limb, a single-primordium organ with morphostatic shaping, in which cells rearrange in response to signalling centres which are essentially unchanged by cell movement. In the case of the tooth, a single-primordium organ with morphodynamic shaping in which the strengths and relationships between signalling centres is influenced by the cell and tissue movements they induce, and the beak, in which the final form is influenced by the collision and rearrangement of multiple tissue primordia, abrupt appearance of qualitatively different forms (i.e. morphological novelties) can occur with small changes in system parameters induced by a genetic change, or by an environmental factor whose effects can be subsequently canalized genetically. Bringing developmental mechanisms and, specifically, the material properties of tissues as excitable media into the evolutionary picture, demonstrates that gradualistic change for incremental adaptive advantage is only one of the possible modes of morphological evolution.
Assuntos
Bico/embriologia , Evolução Biológica , Botões de Extremidades/embriologia , Dente/embriologia , Animais , Bico/anatomia & histologia , Biologia do Desenvolvimento , Extremidades/anatomia & histologia , Extremidades/embriologia , Humanos , Botões de Extremidades/anatomia & histologia , Morfogênese , Dente/anatomia & histologiaRESUMO
The striking diversity of bird beak shapes is an outcome of natural selection, yet the relative importance of the limitations imposed by the process of beak development on generating such variation is unclear. Untangling these factors requires mapping developmental mechanisms over a phylogeny far exceeding model systems studied thus far. We address this issue with a comparative morphometric analysis of beak shape in a diverse group of songbirds. Here we show that the dynamics of the proliferative growth zone must follow restrictive rules to explain the observed variation, with beak diversity constrained to a three parameter family of shapes, parameterized by length, depth and the degree of shear. We experimentally verify these predictions by analysing cell proliferation in the developing embryonic beaks of the zebra finch. Our findings indicate that beak shape variability in many songbirds is strongly constrained by shared properties of the developmental programme controlling the growth zone.
Assuntos
Bico/embriologia , Tentilhões/embriologia , Modelos Biológicos , Morfogênese/fisiologia , Filogenia , Animais , Bico/anatomia & histologia , Pesos e Medidas Corporais , Proliferação de Células , Simulação por Computador , Tentilhões/anatomia & histologia , Seleção GenéticaRESUMO
The tooth is a major component of the vertebrate feeding apparatus and plays a crucial role in species survival, thus subjecting tooth developmental programs to strong selective constraints. However, irrespective of their functional importance, teeth have been lost in multiple lineages of tetrapod vertebrates independently. To understand both the generality and the diversity of developmental mechanisms that cause tooth agenesis in tetrapods, we investigated expression patterns of a series of tooth developmental genes in the lower jaw of toothless turtles and compared them to that of toothed crocodiles and the chicken as a representative of toothless modern birds. In turtle embryos, we found impairment of Shh signaling in the oral epithelium and early-stage arrest of odontoblast development caused by termination of Msx2 expression in the dental mesenchyme. Our data indicate that such changes underlie tooth agenesis in turtles and suggest that the mechanism that leads to early-stage odontogenic arrest differs between birds and turtles. Our results demonstrate that the cellular and molecular mechanisms that regulate early-stage arrest of tooth development are diverse in tetrapod lineages, and odontogenic developmental programs may respond to changes in upstream molecules similarly thereby evolving convergently with feeding morphology.
Assuntos
Bico/anatomia & histologia , Evolução Molecular , Tartarugas/genética , Jacarés e Crocodilos/anatomia & histologia , Jacarés e Crocodilos/embriologia , Jacarés e Crocodilos/genética , Animais , Bico/embriologia , Embrião de Galinha , Galinhas/anatomia & histologia , Galinhas/genética , Regulação da Expressão Gênica no Desenvolvimento , Genes Controladores do Desenvolvimento , Proteínas Hedgehog/genética , Proteínas Hedgehog/metabolismo , Proteínas de Homeodomínio/genética , Proteínas de Homeodomínio/metabolismo , Mandíbula/anatomia & histologia , Mandíbula/metabolismo , Mesoderma/metabolismo , Dente/anatomia & histologia , Dente/embriologia , Tartarugas/anatomia & histologia , Tartarugas/embriologiaRESUMO
The astonishing variation in the shape and size of bird beaks reflects a wide range of dietary specializations that played an important role in avian diversification. Among Darwin's finches, ground finches (Geospiza spp.) have beaks that represent scaling variations of the same shape, which are generated by alterations in the signaling pathways that regulate growth of the two skeletal components of the beak: the prenasal cartilage (pnc) and the premaxillary bone (pmx). Whether this developmental mechanism is responsible for variation within groups of other closely related bird species, however, has remained unknown. Here, we report that the Caribbean bullfinches (Loxigilla spp.), which are closely related to Darwin's finches, have independently evolved beaks of a novel shape, different from Geospiza, but also varying from each other only in scaling. However, despite sharing the same beak shape, the signaling pathways and tissues patterning Loxigilla beaks differ among the three species. In Loxigilla noctis, as in Geospiza, the pnc develops first, shaped by Bmp4 and CaM signaling, followed by the development of the pmx, regulated by TGFßIIr, ß-catenin, and Dkk3 signaling. In contrast, beak morphogenesis in Loxigilla violacea and Loxigilla portoricensis is generated almost exclusively by the pmx through a mechanism in which Ihh and Bmp4 synergize to promote expansion of bone tissue. Together, our results demonstrate high flexibility in the relationship between morphology and underlying developmental causes, where different developmental programs can generate identical shapes, and similar developmental programs can pattern different shapes.
Assuntos
Bico/embriologia , Evolução Biológica , Tentilhões/embriologia , Tentilhões/genética , Morfogênese/fisiologia , Filogenia , Transdução de Sinais/fisiologia , Animais , Sequência de Bases , Teorema de Bayes , Bico/anatomia & histologia , Proteína Morfogenética Óssea 4/metabolismo , Calmodulina/metabolismo , Cartilagem/embriologia , Embrião de Galinha , Ossos Faciais/embriologia , Proteínas Hedgehog/metabolismo , Imuno-Histoquímica , Hibridização In Situ , Modelos Genéticos , Dados de Sequência Molecular , Receptores de Fatores de Crescimento Transformadores beta/metabolismo , Análise de Sequência de DNA , Especificidade da Espécie , beta Catenina/metabolismoRESUMO
Teleost fishes comprise approximately half of all living vertebrates. The extreme range of diversity in teleosts is remarkable, especially, extensive morphological variation in their jaws and dentition. Some of the most unusual dentitions are found among members of the highly derived teleost order Tetraodontiformes, which includes triggerfishes, boxfishes, ocean sunfishes, and pufferfishes. Adult pufferfishes (Tetraodontidae) exhibit a distinctive parrot-like beaked jaw, forming a cutting edge, unlike in any other group of teleosts. Here we show that despite novelty in the structure and development of this "beak," it is initiated by formation of separate first-generation teeth that line the embryonic pufferfish jaw, with timing of development and gene expression patterns conserved from the last common ancestor of osteichthyans. Most of these first-generation larval teeth are lost in development. Continuous tooth replacement proceeds in only four parasymphyseal teeth, as sequentially stacked, multigenerational, jaw-length dentine bands, before development of the functional beak. These data suggest that dental novelties, such as the pufferfish beak, can develop later in ontogeny through modified continuous tooth addition and replacement. We conclude that even highly derived morphological structures like the pufferfish beak form via a conserved developmental bauplan capable of modification during ontogeny by subtle respecification of the developmental module.
Assuntos
Bico/embriologia , Bico/fisiologia , Tetraodontiformes/embriologia , Tetraodontiformes/genética , Dente/embriologia , Dente/fisiologia , Animais , Evolução Biológica , Proteína Morfogenética Óssea 4/genética , Embrião não Mamífero/embriologia , Embrião não Mamífero/fisiologia , Feminino , Regulação da Expressão Gênica no Desenvolvimento/fisiologia , Variação Genética , Proteínas Hedgehog/genética , Proteínas de Homeodomínio/genética , Masculino , Fator de Transcrição PAX9/genética , Fenótipo , Fatores de Transcrição/genética , Proteína Homeobox PITX2RESUMO
The extant monotremes (platypus and echidnas) are believed to all be capable of electroreception in the trigeminal pathways, although they differ significantly in the number and distribution of electroreceptors. It has been argued by some authors that electroreception was first developed in an aquatic environment and that echidnas are descended from a platypus-like ancestor that invaded an available terrestrial habitat. If this were the case, one would expect the developmental trajectories of the trigeminal pathways to be similar in the early stages of platypus and short-beaked echidna development, with structural divergence occurring later. We examined the development of the peripheral trigeminal pathway from snout skin to trigeminal ganglion in sectioned material in the Hill and Hubrecht collections to test for similarities and differences between the two during the development from egg to adulthood. Each monotreme showed a characteristic and different pattern of distribution of developing epidermal sensory gland specializations (electroreceptor primordia) from the time of hatching. The cross-sectional areas of the trigeminal divisions and the volume of the trigeminal ganglion itself were also very different between the two species at embryonic ages, and remained consistently different throughout post-hatching development. Our findings indicate that the trigeminal pathways in the short-beaked echidna and the platypus follow very different developmental trajectories from the earliest ages. These findings are more consistent with the notion that the platypus and echidna have both diverged from an ancestor with rudimentary electroreception and/or trigeminal specialization, rather than the contention that the echidna is derived from a platypus-like ancestor.
Assuntos
Vias Neurais/embriologia , Ornitorrinco , Células Receptoras Sensoriais/fisiologia , Tachyglossidae , Gânglio Trigeminal , Animais , Bico/embriologia , Bico/crescimento & desenvolvimento , Bico/fisiologia , Vias Neurais/crescimento & desenvolvimento , Vias Neurais/fisiologia , Ornitorrinco/embriologia , Ornitorrinco/crescimento & desenvolvimento , Ornitorrinco/fisiologia , Tachyglossidae/embriologia , Tachyglossidae/crescimento & desenvolvimento , Tachyglossidae/fisiologia , Gânglio Trigeminal/embriologia , Gânglio Trigeminal/crescimento & desenvolvimento , Gânglio Trigeminal/fisiologiaRESUMO
All living birds are toothless, constituting by far the most diverse toothless vertebrate clade, and are striking examples of evolutionary success following tooth loss. In recent years, an unprecedented number of Mesozoic birds have been described, illustrating the evolution of dentition reductions. Simultaneously, major advances in experimental embryology have yielded new results concerning avian edentulism. Reviewing these lines of evidence, we propose hypotheses for its causes, with a prominent role for the horny beak during development. A horny beak and a muscular gizzard functionally 'replaced' dentition for food acquisition and processing, respectively. Together with edentulism itself, these features and others contributed to the later success of birds, as a result of their high performance or additional functionality working in concert in these complex organisms.
Assuntos
Bico/fisiologia , Evolução Biológica , Aves/anatomia & histologia , Aves/genética , Moela das Aves/fisiologia , Animais , Bico/anatomia & histologia , Bico/embriologia , Aves/embriologia , Aves/fisiologia , Fósseis , Regulação da Expressão Gênica no Desenvolvimento , Moela das Aves/anatomia & histologia , Moela das Aves/embriologia , Modelos Biológicos , Odontogênese , Filogenia , Seleção Genética , Dente/anatomia & histologia , Dente/embriologia , Dente/fisiologiaRESUMO
Mammals and birds have common embryological facial structures, and appear to employ the same molecular genetic developmental toolkit. We utilized natural variation found in bird beaks to investigate what genes drive vertebrate facial morphogenesis. We employed cross-species microarrays to describe the molecular genetic signatures, developmental signaling pathways and the spectrum of transcription factor (TF) gene expression changes that differ between cranial neural crest cells in the developing beaks of ducks, quails and chickens. Surprisingly, we observed that the neural crest cells established a species-specific TF gene expression profile that predates morphological differences between the species. A total of 232 genes were differentially expressed between the three species. Twenty-two of these genes, including Fgfr2, Jagged2, Msx2, Satb2 and Tgfb3, have been previously implicated in a variety of mammalian craniofacial defects. Seventy-two of the differentially expressed genes overlap with un-cloned loci for human craniofacial disorders, suggesting that our data will provide a valuable candidate gene resource for human craniofacial genetics. The most dramatic changes between species were in the Wnt signaling pathway, including a 20-fold up-regulation of Dkk2, Fzd1 and Wnt1 in the duck compared with the other two species. We functionally validated these changes by demonstrating that spatial domains of Wnt activity differ in avian beaks, and that Wnt signals regulate Bmp pathway activity and promote regional growth in facial prominences. This study is the first of its kind, extending on previous work in Darwin's finches and provides the first large-scale insights into cross-species facial morphogenesis.
Assuntos
Proteínas Aviárias/metabolismo , Aves/embriologia , Aves/genética , Regulação da Expressão Gênica no Desenvolvimento , Fatores de Transcrição/metabolismo , Animais , Proteínas Aviárias/genética , Bico/embriologia , Padronização Corporal , Proteínas Morfogenéticas Ósseas/genética , Proteínas Morfogenéticas Ósseas/metabolismo , Diferenciação Celular , Embrião de Galinha , Galinhas/metabolismo , Anormalidades Craniofaciais/genética , Embrião não Mamífero/metabolismo , Perfilação da Expressão Gênica , Humanos , Morfogênese , Fatores de Transcrição/genética , Proteínas Wnt/genética , Proteínas Wnt/metabolismoRESUMO
Fibroblast growth factors (FGFs) are required for brain, pharyngeal arch, suture and neural crest cell development and mutations in the FGF receptors have been linked to human craniofacial malformations. To study the functions of FGF during facial morphogenesis we locally perturb FGF signalling in the avian facial prominences with FGFR antagonists, foil barriers and FGF2 protein. We tested 4 positions with antagonist-soaked beads but only one of these induced a facial defect. Embryos treated in the lateral frontonasal mass, adjacent to the nasal slit developed cleft beaks. The main mechanisms were a block in proliferation and an increase in apoptosis in those areas that were most dependent on FGF signaling. We inserted foil barriers with the goal of blocking diffusion of FGF ligands out of the lateral edge of the frontonasal mass. The barriers induced an upregulation of the FGF target gene, SPRY2 compared to the control side. Moreover, these changes in expression were associated with deletions of the lateral edge of the premaxillary bone. To determine whether we could replicate the effects of the foil by increasing FGF levels, beads soaked in FGF2 were placed into the lateral edge of the frontonasal mass. There was a significant increase in proliferation and an expansion of the frontonasal mass but the skeletal defects were minor and not the same as those produced by the foil. Instead it is more likely that the foil repressed FGF signaling perhaps mediated by the increase in SPRY2 expression. In summary, we have found that the nasal slit is a source of FGF signals and the function of FGF is to stimulate proliferation in the cranial frontonasal mass. The FGF independent regions correlate with those previously determined to be dependent on BMP signaling. We propose a new model whereby, FGF-dependent microenvironments exist in the cranial frontonasal mass and caudal maxillary prominence and these flank BMP-dependent regions. Coordination of the proliferation in these regions leads ultimately to normal facial morphogenesis.
Assuntos
Embrião de Galinha , Face/embriologia , Fatores de Crescimento de Fibroblastos/metabolismo , Morfogênese , Animais , Bico/embriologia , Galinhas , Patos/embriologia , Peptídeos e Proteínas de Sinalização Intercelular/metabolismo , Pirróis/farmacologia , Receptores de Fatores de Crescimento de Fibroblastos/antagonistas & inibidores , Especificidade da EspécieRESUMO
The frontonasal prominence of the developing avian embryo contains an organizing center, defined by juxtaposition of the Sonic hedgehog (Shh) and Fibroblast growth factor 8 (Fgf8) expression domains. This molecular interface presages any detectable growth of the frontonasal prominence, and experiments involving transplantation of this boundary epithelium have demonstrated it is a source of dorsal-ventral and rostral-caudal patterning information for the neural crest-derived mesenchyme of the upper beak. We explored the ontogeny of this organizing center by mapping the expression domains of both genes and their receptors and downstream targets. We tested the extent to which Shh and Fgf8 regulate each other's expression in this frontonasal organizer by either blocking or ectopically activating these pathways. Our experiments revealed mutual antagonism between the two molecules, which aids in establishing and maintaining a molecular boundary that subsequently influences patterning and growth of the middle and upper face.
Assuntos
Face/embriologia , Fator 8 de Crescimento de Fibroblasto/metabolismo , Proteínas Hedgehog/metabolismo , Animais , Bico/embriologia , Padronização Corporal , Embrião de Galinha , Ectoderma/embriologia , Fator 8 de Crescimento de Fibroblasto/genética , Regulação da Expressão Gênica no Desenvolvimento/fisiologia , Proteínas Hedgehog/genética , Hibridização In Situ , Transdução de SinaisRESUMO
The purpose of this study is to delineate with high frequency ultrasound imaging the normal growth and development of the chick embryo throughout its incubation period. White Leghorn chick embryos were imaged through an opening in the egg air cell from incubation day 0-19 (Hamburger & Hamilton stage 1-45) using a 13 MHz clinical high frequency linear small parts transducer. Multiple anatomic growth parameters were measured. Normal growth was confirmed with Hamburger and Hamilton staging. A timeline was constructed showing when each anatomic growth parameter could be visualized. Means and standard deviations of each parameter were plotted against incubation days studied to create nomograms and numerical tables of normal growth and development of the chick embryo. With this set of data, abnormal growth and development of the chick embryo can now be assessed.