CADHERIN-MEDIATED CELL-INTERACTIONS ARE NECESSARY FOR THE ACTIVATION OF MYOD IN XENOPUS MESODERM

Muscle progenitors in Xenopus interact in a community of 100 or more c ells to activate their myogenic genes and the muscle differentiation p athway. We examine whether the cell adhesion molecule cadherin is invo lved in this process. Injections of dominant negative N-cadherin RNA i nto the region of 2- to 4-cell embryos that will give rise to muscle s uppress MyoD expression in muscle progenitor cells. By contrast, Xbra expression is unaffected and levels of Xwnt-8 message rise with increa sing doses of dominant negative cadherin RNA. MyoD inhibition in embry os injected with the dominant negative cadherin mRNA is rescued by coi njection of full-length cadherin RNA; showing that the inhibition of M yoD occurs through the cadherin pathway. These results show that cadhe rin-mediated cell interactions play a critical role in the signaling e vents required for muscle progenitor cells to differentiate, as judged by their stable activation of MyoD.