Calcium mediates dorsoventral patterning of mesoderm in Xenopus

Calcium signals participate in the differentiation of electrically excitabl e and nonexcitable cells; one example of this differentiation is the acquis ition of mature neuronal phenotypes Ell. For example, transient elevations of the intracellular calcium concentration have been recorded in the ectode rm of early embryos, and this elevation has been proposed to participate in neural induction [2-5]. Here, we present molecular evidence indicating tha t voltage-sensitive calcium channels (VSCC) are involved in early developme ntal processes leading to the establishment of the dorsoventral (D-V) patte rning of a vertebrate embryo. We report that alpha S-1 VSCC are expressed s electively in the dorsal marginal zone at the early gastrula stage. The exp ression of the VSCC correlates with elevated intracellular calcium levels, as evaluated by the fluorescence of the intracellular calcium indicator Flu o-3. Misexpression of VSCC leads to a strong dorsalization of the ventral m arginal zone and induction of the secondary axis but no direct neuralizatio n of the ectoderm. Moreover, specific inhibition of VSCC by the use of calc icludine results in ventralization of the dorsal mesoderm. Together, these results indicate that calcium channels regulate mesodermal patterning by sp ecificating the D-V identity of the mesodermal cells. The D-V patterning of the mesoderm has been shown to depend on a gradient of BMPs activity. We d iscuss the possibility that VSCC affect or act downstream of BMPs activity.