Induction of the mesendoderm in the zebrafish germ ring by yolk cell-derived TGF-beta family signals and discrimination of mesoderm and endoderm by FGF.

摘要: The endoderm forms the gut and associated organs, develops from a layer of cells which emerges during gastrula stages in vertebrate embryo. In comparison to mesoderm ectoderm, little is known about signals induce endoderm. origin intimately linked with that mesoderm, both by their position embryo, molecules can them. We characterised gene, zebrafish gata5, expressed blastula show its transcription induced originating yolk cell. These also mesoderm-expressed factor no tail (ntl), whose initial expression coincides gata5 closest blastoderm margin, then spreads encompass germ ring. have induction these genes ectopic activin induces ntl pattern mimics endogenous expression, while dominant negative receptor abolishes expression. Injection RNA encoding constitutively active leads ntl. activated cell-autonomously, whereas distant those received RNA, showing although TGF-beta signal, relay mechanism. Expression fibroblast growth (eFGF) or negatively acting FGF shows but not regulated signalling, implying this may be signal leading spread embryos lacking squint cyclops, members nodal group related molecules, abolished, making factors primary candidates for inducing gata5.