Studying The Mechanisms Of Mespo Gene Expression In Xenopus Somitogenesis

The vertebral column is derived from somites, which are transient segments of the paraxial mesoderm that are present in developing vertebrates. The strict spatial and temporal regulation of somitogenesis is of crucial developmental importance. Signals such as Wnt, FGF and RA play roles in somitogenesis, but many details of how these signals function in this process remain unclear. Mespo, a member of bHLH transcription factor family plays important roles in specification of the paraxial mesoderm and regulation of segmentation. However, mechanisms that regulate the expression of Mespo are unclear. Some evidence has shown that Mespo might be regulated by these signals. To address these questions, we isolated a genomic DNA sequence containing 4317 bp of Mespo 5'flanking region in Xenopus. Luciferase assays show that this upstream sequence has a transcription activity. A 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. Luciferase assay shows that this upstream sequence can respond to Wnt signaling. Transgenic analysis of the Mespo promoter identifies Mespo as a direct downstream target of Wnt/?-catenin signaling pathway. We also show that activity of Wnt/?-catenin signaling in somitogenesis can be enhanced by the PI3-K/AKT pathway. Our data illustrate that Wnt/?-catenin signaling in conjunction with PI3-K/AKT pathway plays a key role in controlling development of the paraxial mesoderm. We further mapped a 326 bp DNA sequence responding to RA signaling. These results shed light on how regulation of Mespo expression is controlled, and this finding provides a powerful tool to study how signaling pathways interact to regulate development of paraxial mesoderm.