RESUMO
The mesencephalic and metencephalic region (MMR) of the vertebrate central nervous system develops in response to signals produced by the isthmic organizer (IsO). We have previously reported that the LIM homeobox transcription factor Lmx1b is expressed within the chick IsO, where it is sufficient to maintain expression of the secreted factor wnt1. In this paper, we show that zebrafish express two Lmx1b orthologs, lmx1b.1 and lmx1b.2, in the rostral IsO, and demonstrate that these genes are necessary for key aspects of MMR development. Simultaneous knockdown of Lmx1b.1 and Lmx1b.2 using morpholino antisense oligos results in a loss of wnt1, wnt3a, wnt10b, pax8 and fgf8 expression at the IsO, leading ultimately to programmed cell death and the loss of the isthmic constriction and cerebellum. Single morpholino knockdown of either Lmx1b.1 or Lmx1b.2 has no discernible effect on MMR development. Maintenance of lmx1b.1 and lmx1b.2 expression at the isthmus requires the function of no isthmus/pax2.1, as well as Fgf signaling. Transient misexpression of Lmx1b.1 or Lmx1b.2 during early MMR development induces ectopic wnt1 and fgf8 expression in the MMR, as well as throughout much of the embryo. We propose that Lmx1b.1- and Lmx1b.2-mediated regulation of wnt1, wnt3a, wnt10b, pax8 and fgf8 maintains cell survival in the isthmocerebellar region.
Assuntos
Proteínas de Homeodomínio/fisiologia , Mesencéfalo/embriologia , Metencéfalo/embriologia , Fatores de Transcrição/fisiologia , Peixe-Zebra/embriologia , Sequência de Aminoácidos , Animais , Proteínas de Ligação a DNA/metabolismo , Fator 8 de Crescimento de Fibroblasto , Fatores de Crescimento de Fibroblastos/genética , Fatores de Crescimento de Fibroblastos/metabolismo , Regulação da Expressão Gênica no Desenvolvimento/fisiologia , Proteínas de Homeodomínio/genética , Peptídeos e Proteínas de Sinalização Intercelular/biossíntese , Peptídeos e Proteínas de Sinalização Intercelular/genética , Proteínas com Homeodomínio LIM , Dados de Sequência Molecular , Fator de Transcrição PAX2 , Isoformas de Proteínas/genética , Isoformas de Proteínas/fisiologia , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Proteínas Wnt , Proteína Wnt1 , Peixe-Zebra/genética , Proteínas de Peixe-ZebraRESUMO
Blimp is a transcriptional repressor that has been identified in humans, mice and frogs. Here, we describe the cloning of the gene that encodes for the chick homolog of Blimp, cBlimp-1, and the tempo-spatial expression pattern of cBlimp-1, during chick development. cBlimp-1 whose gene product shares a high level of identity with its homologs from other organisms, was found to be expressed in the apical ectodermal ridge and posterior dorsal ectoderm of developing limb buds. In addition, cBlimp-1 is expressed in the developing eyes, branchial arches and otic placodes.
