Hypaxial muscle migration during primary myogenesis in Xenopus laevis

In contrast to many vertebrates, the ventral body wall muscles and limb mus cles of Xenopus develop at different times. The ventral body wall forms in the tadpole, while limb (appendicular) muscles form during metamorphosis to the adult frog. In organisms that have been examined thus far, a conserved mechanism has been shown to control migratory muscle precursor specificati on, migration, and differentiation. Here, we show that the process of ventr al body wall formation in Xenopus laevis is similar to hypaxial muscle deve lopment in chickens and mice. Cells specified for the migratory lineage dis play an upregulation of pax3 in the ventro-lateral region of the somite. Th ese pax3-positive cells migrate ventrally, away from the somite, and underg o terminal differentiation with the expression of myf-5, followed by myoD. Several other genes are selectively expressed in the migrating muscle precu rsor population, including neural cell adhesion molecule (NCAM, Xenopus kit related kinase (Xkrk1), and Xenopus SRY box 5 (sox5). We have also found t hat muscle precursor migration is highly coordinated with the migration of neural crest-derived melanophores. However, by extirpating neural crest at an early stage and allowing embryos to develop, we determined that muscle p recursor migration is not dependent on physical or genetic interaction with melanophores. (C) 2001 Academic Press.