RESUMO
Many chordate-specific morphological features develop depending on retinoic acid (RA). We isolated cDNA clones encoding a retinoic acid receptor (CiRAR) and a retinoid X receptor (CiRXR) in the ascidian Ciona intestinalis. CiRAR mRNA was detected in the anterior ectoderm and endoderm during gastrulation. The expression persists in the head endoderm and two discrete regions of the nerve cord in the tailbud embryo. CiRXR mRNA was ubiquitously expressed. RA affected closure of the neural tube and formation of the adhesive papillae. However, no obvious upregulation in CiRAR expression was observed. Expression of some, but not all, of the neural and papilla-specific genes was reduced in the RA-treated embryo. These results suggest limited roles of CiRAR in ascidian embryos.
Assuntos
Ciona intestinalis/embriologia , Ciona intestinalis/genética , Regulação da Expressão Gênica no Desenvolvimento , Receptores do Ácido Retinoico/genética , Tretinoína/metabolismo , Sequência de Aminoácidos , Animais , Padronização Corporal/genética , Embrião não Mamífero/efeitos dos fármacos , Regulação da Expressão Gênica no Desenvolvimento/efeitos dos fármacos , Marcadores Genéticos , Dados de Sequência Molecular , Morfogênese/genética , Receptores do Ácido Retinoico/metabolismo , Receptores X de Retinoides , Homologia de Sequência de Aminoácidos , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Tretinoína/farmacologia , Regulação para CimaRESUMO
Spatially regulated synthesis and degradation of retinoic acid (RA) organize embryonic pattern formation in vertebrate embryos. Here, we show expression pattern of genes encoding Ciona intestinalis homologs of the retinaldehyde dehydrogenase, RALDH2, and the cytochrome P450 RA-degrading enzyme, CYP26, in normal and RA-treated embryos. The Ciona homolog of Raldh2, Ci-Raldh2, was expressed in a few muscle-lineage blastomeres in the middle gastrula. Strong expression was then restricted to the anterior-most three muscle cells on each side of the tailbud embryo. The Ciona homolog of Cyp26, Ci-Cyp26, was expressed in the presumptive brain cells in the middle gastrula. The expression was then upregulated in the neck region. The posterior end of the tail was also weakly stained. Non-overlapping expression domains of Ci-Raldh2 and Ci-Cyp26 look similar to those in vertebrates, although the expression of both genes was restricted to a small number of cells in Ciona embryos. RA upregulated Ci-Cyp26 expression and slightly downregulated Ci-Raldh2 expression in the tailbud embryo. We also show expression pattern of a Hox-1 ortholog (CiHox-1) in the Ciona embryo. CiHox-1 was expressed in two separated regions of the nerve cord and neck epidermis at the neurula stage. Expression pattern of these three genes are essentially similar to that in vertebrates.
Assuntos
Aldeído Oxirredutases/genética , Ciona intestinalis/embriologia , Sistema Enzimático do Citocromo P-450/genética , Proteínas de Homeodomínio/genética , Tretinoína/metabolismo , Aldeído Oxirredutases/biossíntese , Sequência de Aminoácidos , Animais , Sítios de Ligação , Sistema Enzimático do Citocromo P-450/biossíntese , Gástrula/metabolismo , Proteínas de Homeodomínio/biossíntese , Dados de Sequência Molecular , NAD/metabolismo , Sistema Nervoso/embriologia , Retinal Desidrogenase , Ácido Retinoico 4 HidroxilaseRESUMO
The neural crest is a population of mitotically active, multipotent progenitor cells that arise at the neural plate border. Neural crest progenitors must be maintained in a multipotent state until after neural tube closure. However, the molecular underpinnings of this process have yet to be fully elucidated. Here we show that the basic helix-loop-helix (bHLH) transcriptional repressor gene, Xenopus hairy2 (Xhairy2), is an essential early regulator of neural crest formation in Xenopus. During gastrulation, Xhairy2 is localized at the presumptive neural crest prior to the expression of such neural crest markers as Slug and FoxD3. Morpholino-mediated knockdown of Xhairy2 results in the repression of neural crest marker gene expression while inducing the ectopic expression of the cell cycle inhibitor p27(xic1) in the presumptive neural crest. We also found that ectopic p27(xic1) disturbs neural crest formation. Furthermore, the depletion of Xhairy2 leads to the apoptosis of mitotic cells. Our results suggest that Xhairy2 functions in neural crest specification by maintaining cells in the mitotic and undifferentiated state.