Calcium signaling in the developing Xenopus myotome

Embryonic Xenopus myocytes generate spontaneous calcium (Ca2+) transients d uring differentiation in culture. Suppression of these transients disrupts myofibril organization and the formation of sarcomeres through an identifie d signal transduction cascade. Since transients often occur during myocyte polarization and migration in culture, we hypothesized they might play addi tional roles in vivo during tissue formation. We have tested this hypothesi s by examining Ca2+ dynamics in the intact Xenopus paraxial mesoderm as it differentiates into the mature myotome. We find that Ca2+ transients occur in cells of the developing myotome with characteristics remarkably similar to those in cultured myocytes. Transients produced within the myotome are c orrelated with somitogenesis as well as myocyte maturation. Since transient s arise from intracellular stores in cultured myocytes, we examined the fun ctional distribution of both IP3 and ryanodine receptors in the intact myot ome by eliciting Ca2+ elevations in response to photorelease of caged IP3 a nd superfusion of caffeine, respectively. As in culture, transients in vivo depend on Ca2+ release from ryanodine receptor (RyR) stores, and blocking RyR during development interferes with somite maturation. (C) 1999 Academic Press.