Divergent regulation of Wnt-mediated development of the dorsomedial and ventrolateral dermomyotomal lips.

The dermomyotome is the dorsal compartment of the somite which gives rise to multiple cell fates including skeletal muscle, connective tissue, and endothelia. It consists of a pseudostratified, roughly rectangular epithelial sheet, the margins of which are called the dermomyotomal lips. The dermomyotomal lips are blastema-like epithelial growth zones, which continuously give rise to resident dermomyotomal cells and emigrating muscle precursor cells, which populate the subjacent myotomal compartment. Wnt signaling has been shown to regulate both dermomyotome formation and maintenance of the dermomyotomal lips. Whereas the epithelialization of the dermomyotome is regulated via canonical, β-catenin-dependent Wnt signaling, the downstream signaling mechanisms suppressing epithelial-mesenchymal transition (EMT) in the mature dermomyotomal lips have been unknown. Here, we present evidence that dermomyotomal lip sustainment is differentially regulated. Whereas the dorsomedial dermomyotomal lip is maintained by canonical Wnt signaling, development of the ventrolateral dermomyotomal lip is regulated by non-canonical, PCP-like Wnt signaling. We discuss our results in the light of the different developmental prerequisites in the dorsomedial and ventrolateral lips, respectively, thus providing a new perspective on the regulation of dermomyotomal EMT.