RESUMO
A complete zebrafish mespo cDNA encoding a protein of 131 amino acids with a bHLH domain in the C-terminal has been isolated. The bHLH domain of zebrafish Mespo is highly similar to those in the mouse, chick and Xenopus, sharing 82.4%, 80.4% and 74.5% amino acid identity, respectively. At 50% epiboly, the zebrafish mespo is first detected in the marginal zone of the blastoderm but excluding the prospective shield. Subsequently, mespo expression is intensified in the involuting mesoderm at 60% epiboly, and then restricted to the presomitic mesoderm (PSM) at 95% epiboly. At the 1-somite stage, mespo expression becomes reduced in the most rostral PSM. During segmentation, mespo expression is gradually downregulated at the most rostral segmental plate where cells are being coalesced to form somites. In spadetail mutant embryos, most of mespo-expressing cells were missing.
Assuntos
Regulação da Expressão Gênica no Desenvolvimento , Mesoderma/fisiologia , Fatores de Transcrição/genética , Proteínas de Peixe-Zebra/genética , Peixe-Zebra/genética , Sequência de Aminoácidos , Animais , Fatores de Transcrição Hélice-Alça-Hélice Básicos , Embrião não Mamífero , Extremidades/embriologia , Sequências Hélice-Alça-Hélice , Mesoderma/citologia , Dados de Sequência Molecular , Mutação , Homologia de Sequência de Aminoácidos , Proteínas com Domínio T/genética , Transativadores/genética , Fatores de Transcrição/metabolismo , Proteínas de Xenopus/genética , Peixe-Zebra/embriologia , Proteínas de Peixe-Zebra/metabolismoRESUMO
Wnts have been shown to provide a posteriorizing signal that has to be repressed in the anterior neuroectoderm for normal anteroposterior (AP) patterning. We have previously identified a zebrafish frizzled8a (fz8a) gene expressed in the presumptive anterior neuroectoderm as well as prechordal plate at the late gastrula stage. We have investigated the role of Fz8a-mediated Wnt8b signalling in anterior brain patterning in zebrafish. We show that in zebrafish embryos: (1) Wnt signalling has at least two different stage-specific posteriorizing activities in the anterior neuroectoderm, one before mid-gastrulation and the other at late gastrulation; (2) Fz8a plays an important role in mediating anterior brain patterning; (3) Wnt8b and Fz8a can functionally interact to transmit posteriorizing signals that determine the fate of the posterior diencephalon and midbrain in late gastrula embryos; and (4) Wnt8b can suppress fz8a expression in the anterior neuroectoderm and potentially affect the level and/or range of Wnt signalling. In conclusion, we suggest that a gradient of Fz8a-mediated Wnt8b signalling may play crucial role in patterning the posterior diencephalon and midbrain regions in the late gastrula.