Mesp-family genes are required for segmental patterning and segmental border formation

Abstract

Elaborate somite patterning is based on the dynamic gene regulation within the presomitic mesoderm (PSM) derived from the primitive streak and tailbud in the later stage embryo. Notch signaling and the regulators are major players involved in the all events required for the temporally and spatially coordinated somite formation. PSM can be subdivided at least two domains based on the regulation and maybe the function of genes expressed. In the posterior PSM, a basic-HLH protein Hes7 plays a central role to generate traveling wave of gene expression by negatively regulating the transcription of the target genes, which may lead defining soimte spacing and future segmental unit. In the anterior PSM, cells start to prepare segmental pattering by acquiring rostral or caudal identity of somite primordia and defining segmental border. In this process, Mesp2, another basic HLH protein plays a critical role. Genetic evidence is provided how Mesp2 regulates Notch signaling to establish segmental identity in the anterior PSM. © 2009 Springer New York.