Desensitization of IP3-induced Ca2+ release by overexpression of a constitutively active Gq alpha protein converts ventral to dorsal fate in Xenopus early embryos

The constitutively active Gq alpha mutant construct (Gq alpha Q-L) in Xenop us early embryos was overexpressed and the effects on dorsoventral patterni ng examined. It was found that prolonged stimulation of inositol 1,4,5-tris phosphate (IP3)-Ca2+ signaling by overexpression of Gq alpha Q-L led to des ensitization of IP3-induced Ca2+ release (IICR). Desensitization of IICR on the ventral side specifically induced an ectopic dorsal axis due to the co nversion of ventral marginal mesoderm to adopt a dorsal fate. This effect o f desensitization resembles that of inhibitory antibodies against the IP3 r eceptor, as reported previously. These results strengthen the earlier findi ng that active IP3-Ca2+ signaling functions in ventral signaling during the early embryonic development of Xenopus. Furthermore, the nature of downreg ulation of the Xenopus IP3 receptor through continuous stimulation of IP3-C a2+ signaling might play a role in regulating endogenous IP3-Ca2+ signaling in Xenopus early development.