The spatio-temporal expression of connexin43 in Xenopus laevis embryos was studied by in situ hybridization. Cx43 expression is first detected at stage 25 in the developing eye. In stage 32, expression was found in the margin of the lens placode, the cement gland, notochord, and in stage 37 in the branchial arches. Early limb buds show strong expression of Cx43 distally while later on expression is confined to sites of precartilage condensation.

The spatio-temporal expression pattern of the connexin43 gene during Xenopus development has been described (Van der Heyden et al. 2001). To further investigate the regulation and function of connexin43 (Cx43) in amphibians, we have isolated the gene from Xenopus tropicalis (Xt) and determined its structure. The X. tropicalis Cx43 gene displays the typical two exon-one intron connexin configuration, where the first exon is non-coding. The predicted amino acid sequence of the XtCx43 protein is highly homologous to that of X. laevis, chicken and mammals. Expression of XtCx43 cDNA in N2A cells results in gap-junction plaque formation. Promoter activity of a 3.5 kb upstream region of the X. tropicalis Cx43 gene, including exon 1, mimics endogenous timing of expression after injection of reporter constructs in X. laevis embryos.