Expression of L-type Ca2+ channel during early embryogenesis in Xenopus laevis.

The mechanisms involved in the first step of neurogenesis, i.e. neural induction, are poorly understood, particularly in terms of the signalling pathway. In a recent work it has been shown that in urodeles the activation of L-type calcium channels is sufficient to trigger neural induction. In order to substantiate a possible role of this channel in early development in anurans, we have detailed the kinetics of the expression and the localization of the alpha 1 subunit of L-type calcium channel in the early stages of Xenopus laevis embryogenesis using immunological techniques. We observed that the expression of the alpha 1 subunit started during blastulation, where a cytoplasmic labeling was observed. At the onset of gastrulation alpha 1 was targeted to the plasma membrane of the dorsal and the ventral ectoderm. Some labeling was found in the mesoderm but never in the endoderm. This expression seems to be general, since similar results have been obtained in anurans (Xenopus) and in urodeles (Pleurodeles). In addition, we found that the alpha 0 subunit of the G(o) protein is expressed simultaneously and strictly colocalized with the alpha 1 subunit of the L-type calcium channel. The role of this channel and its regulation by G(o) protein during early neurogenesis is discussed.