Two Drosophila innexins are expressed in overlapping domains and cooperateto form gap-junction channels

Members of the innexin protein family are structural components of inverteb rate gap junctions and are analogous to vertebrate connexins. Here we inves tigate two Drosophila innexin genes, Dm-inx2 and Dm-inx3 and show that they are expressed in overlapping domains throughout embryogenesis, most notabl y in epidermal cells bordering each segment. We also explore the gap-juncti on-forming capabilities of the encoded proteins. In paired Xenopus oocytes, the injection of Dm-inx2 mRNA results Fn the formation of voltage-sensitiv e channels in only similar to 40% of cell pairs. In contrast, Dm-Inx3 never forms channels. Crucially, when both mRNAs are coexpressed, functional cha nnels are formed reliably, and the electrophysiological properties of these channels distinguish them from those formed by Dm-Inx2 alone. We relate th ese in vitro data to in vivo studies. Ectopic expression of Dm-inx2 in vivo has limited effects on the viability of Drosophila, and animals ectopicall y expressing Dm-inx3 are unaffected. However, ectopic expression of both tr anscripts together severely reduces viability, presumably because of the fo rmation of inappropriate gap junctions. We conclude that Dm-Inx2 and Dm-Inx 3, which are expressed in overlapping domains during embryogenesis, can for m oligomeric gap-junction channels.