MODULATION OF EMBRYONIC INTRACELLULAR CA2-5A( SIGNALING BY WNT)

Wnt genes encode secreted proteins which are implicated in receptor-me diated cell-cell signaling events important in embryogenesis, but the second messenger systems modulated by Wnfs have not been identified. W e report that ectopic expression of Xwnt-5A in zebrafish embryos enhan ces the frequency of intracellular Ca2+ transients in the enveloping l ayer of the blastodisc, whereas Xwnt-8 does not. These transients are independent of extracellular Ca2+. Consistent with the observed Ca2+ t ransients playing a role in responses of embryos to Xwnt-5A, We report that the ligand-activated serotonin type 1C receptor, which stimulate s PI cycle activity and Ca2+ signaling independent of Wnts, phenocopie s embryonic responses to Xwnt-5A. These results suggest that intercell ular signaling by a subset of vertebrate Wnts involves modulation of a intracellular Ca2+ signaling pathway, which may arise from phosphatid ylinositol cycle activity. (C) 1997 Academic Press.