Calcium transients triggered by planar signals induce the expression of ZIC3 gene during neural induction in Xenopus

Abstract

In intact Xenopus embryos, an increase in intracellular Ca2+ in the dorsal ectoderm is both necessary and sufficient to commit the ectoderm to a neural fate. However, the relationship between this Ca2+ increase and the expression of early neural genes is as yet unknown. In intact embryos, studying the interaction between Ca2+ signaling and gene expression during neural induction is complicated by the fact that the dorsal ectoderm receives both planar and vertical signals from the mesoderm. The experimental system may be simplified by using Keller open-face explants where vertical signals are eliminated, thus allowing the interaction between planar signals, Ca2+ transients, and neural induction to be explored. We have imaged Ca2+ dynamics during neural induction in open-face explants by using aequorin. Planar signals generated by the mesoderm induced localized Ca 2+ transients in groups of cells in the ectoderm. These transients resulted from the activation of L-type Ca2+ channels. The accumulated Ca2+ pattern correlated with the expression of the early neural precursor gene, Zic3. When the transients were blocked with pharmacological agents, the level of Zic3 expression was dramatically reduced. These data indicate that, in open-face explants, planar signals reproduce Ca2+ -signaling patterns similar to those observed in the dorsal ectoderm of intact embryos and that the accumulated effect of the localized Ca2+ transients over time may play a role in controlling the expression pattern of Zic3. © 2003 Elsevier Inc. All rights reserved.