Cloning and analyzing of Xenopus Mespo promoter in retinoic acid regulated Mespo expression.

During vertebrate embryogenesis, presomitic mesoderm cells enter a segmental program to generate somite, a process termed somitogenesis. Mespo, a member of the bHLH transcription factor family, plays important roles in this process. However, how Mespo expression is regulated remains unclear. To address this question, we isolated a genomic DNA sequence containing 4317 bp of Mespo 5' flanking region in Xenopus. Luciferase assays show that this upstream sequence has transcription activity. Transgenic assay shows that this genomic contig is sufficient to recapitulate the dynamic stage- and tissue-specific expression pattern of endogenous Mespo from the gastrula to the tailbud stage. We further mapped a 326 bp DNA sequence responding to retinoic acid signaling. These results shed light on how Mespo expression is regulated, and suggest that retinoic acid signaling pathways play roles in somitogenesis through regulating Mespo.