The involvement of cAMP signaling pathway in axis specification in Xenopus embryos.

The cAMP signaling system has been postulated to be involved in embryogenesis of many animal species, however, little is known about its role in embryonic axis formation in vertebrates. In this study, the role of the cAMP signaling pathway in patterning the body plan of the Xenopus embryo was investigated by expressing and activating the exogenous human 5-hydroxytryptamine type 1a receptor (5-HT(1a)R) which inhibits adenylyl cyclase through inhibitory G-protein in embryos in a spatially- and temporally-controlled manner. In embryos, ventral, but not dorsal expression and stimulation of this receptor during blastula and gastrula stages induced secondary axes but were lacking anterior structures. At the molecular level, 5-HT(1a)R stimulation induced expression of the dorsal mesoderm marker genes, and downregulated expression of the ventral markers but had no effect on expression of the pan mesodermal marker gene in ventral marginal zone explants. In addition, ventral expression and stimulation of the receptor partially restored dorsal axis of UV-irradiated axis deficient embryo. Finally, the total mass of cAMP differs between dorsal and ventral regions of blastula and gastrula embryos and this is regulated in a temporally-specific manner. These results suggest that the cAMP signaling system may be involved in the transduction of ventral signals in patterning early embryos.