RESUMO
In vertebrates, the engrailed genes are expressed at early neurula stage in a narrow stripe encompassing the midbrain-hindbrain boundary (MHB), a region from which a peculiar structure, the isthmus, is formed. Knock-out experiments in mice demonstrated that these genes are essential for the development of this structure and of its derivatives. In contrast, little is known about the effect of an overexpression of engrailed genes in vertebrate development. Here we report the isolation of Ol-eng2, a medaka fish (Oryzias latipes) engrailed gene. We have monitored the effects of its widespread expression following mRNA injections in 1- and 2-cell medaka and Xenopus embryos. We found that the ectopic expression of Ol-eng2 predominantly results in an altered development of the anterior brain, including an inhibition of optic vesicle formation. No change in the patterns of mesencephalic and telencephalic markers were observed. In contrast, expressions of markers of the diencephalon were strongly repressed in injected embryos. Furthermore, the endogenous Ol-eng2, Pax2, Wnt1 and Fgf8, which are essential components of the MHB genetic cascade, were ectopically expressed in this region. Therefore, we propose that Ol-eng2 induces de novo formation of an isthmus-like structure, which correlates with the development of ectopic midbrain structures, including optic tectum. A competence of the diencephalon to change to a midbrain fate has been demonstrated in isthmic graft experiments. Our data demonstrate that this change can be mimicked by ectopic engrailed expression alone.
Assuntos
Diencéfalo/embriologia , Proteínas de Homeodomínio/genética , Mesencéfalo/embriologia , Proteínas do Tecido Nervoso/genética , Oryzias/embriologia , Oryzias/genética , Rombencéfalo/embriologia , Sequência de Aminoácidos , Animais , Sequência de Bases , Padronização Corporal/genética , Primers do DNA/genética , DNA Complementar/genética , Regulação da Expressão Gênica no Desenvolvimento , Genes Homeobox , Hibridização In Situ , Camundongos , Microinjeções , Dados de Sequência Molecular , RNA Mensageiro/administração & dosagem , RNA Mensageiro/genética , Homologia de Sequência de AminoácidosRESUMO
We have identified a member of the insulin receptor (InsR)/insulin-like growth factor-1 receptor (IGF-1R) family. The Xenopus insulin receptor (Xe-InsR) is present as a maternal 6.6 kb transcript. Northern blot analysis reveals the presence of this transcript until the mid-blastula transition (MBT), when levels decrease. At neurulation, two distinct transcripts of 6.6 and 7.7 kb are detected, both of which persist throughout embryogenesis. In situ hybridization analysis shows that InsR expression is restricted to regions of ectodermal and mesodermal origin, notably the encephalon, otic vesicles, optic vesicles, gills, somites and the pronephros.