RESUMO
A detailed fate map was obtained for the early chick neural plate (stages 3d/4). Numerous overlapping plug grafts were performed upon New-cultured chick embryos, using fixable carboxyfluorescein diacetate succinimidyl ester to label donor chick tissue. The specimens were harvested 24 hours after grafting and reached in most cases stages 9-11 (early neural tube). The label was detected immunocytochemically in wholemounts, and cross-sections were later obtained. The positions of the graft-derived cells were classified first into sets of purely neural, purely non-neural and mixed grafts. Comparisons between these sets established the neural plate boundary at stages 3d/4. Further analysis categorized graft contributions to anteroposterior and dorsoventral subdivisions of the early neural tube, including data on the floor plate and the eye field. The rostral boundary of the neural plate was contained within the earliest expression domain of the Ganf gene, and the overall shape of the neural plate was contrasted and discussed with regard to the expression patterns of the genes Plato, Sox2, Otx2 and Dlx5 (and others reported in the literature) at stages 3d/4.
Assuntos
Sistema Nervoso/embriologia , Animais , Padronização Corporal , Embrião de Galinha , Proteínas de Ligação a DNA/genética , Fluoresceínas/química , Regulação da Expressão Gênica no Desenvolvimento , Proteínas HMGB , Proteínas de Homeodomínio/genética , Proteínas do Tecido Nervoso/genética , Sistema Nervoso/citologia , Proteínas Nucleares/genética , Técnicas de Cultura de Órgãos/métodos , Fatores de Transcrição Otx , Prosencéfalo/embriologia , Prosencéfalo/transplante , Fatores de Transcrição SOXB1 , Succinimidas/química , Transativadores/genética , Fatores de Transcrição , TransplantesRESUMO
In Xenopus embryos neural specification takes place by inhibition of epithelial specification, allowing blastoderm cells to continue their previously established neural determination process. This mechanism has been termed neural induction as a "default state". The understanding of this model has been completed with the identification of molecules that can block the epithelial inducers. The antagonist mechanism between epithelial signals (bone morphogenetic proteins [BMPs]) and their blocking agents (BMP antagonists) can explain the formation of the prospective neural territory and why these BMP antagonists function as neural inducers when over-expressed in Xenopus. Despite this well understood mechanism in amphibians, little information is available for other species. The formation of the neural plate by means of a "default state" mechanism in other vertebrates still lacks experimental confirmation. We present evidence that the growth factors of the BMP family are also epithelial inducers in bird embryos, and that when over-expressed they can partially block neural induction.
