title: Two Drosophila innexins are expressed in overlapping domains and cooperate to form gap-junction channels.
abstract: Members of the innexin protein family are structural components of invertebrate gap junctions and are analogous to vertebrate connexins. Here we investigate two Drosophila innexin genes, Dm-inx2 and Dm-inx3 and show that they are expressed in overlapping domains throughout embryogenesis, most notably in epidermal cells bordering each segment. We also explore the gap-junction-forming capabilities of the encoded proteins. In paired Xenopus oocytes, the injection of Dm-inx2 mRNA results in the formation of voltage-sensitive channels in only approximately 40% of cell pairs. In contrast, Dm-Inx3 never forms channels. Crucially, when both mRNAs are coexpressed, functional channels are formed reliably, and the electrophysiological properties of these channels distinguish them from those formed by Dm-Inx2 alone. We relate these in vitro data to in vivo studies. Ectopic expression of Dm-inx2 in vivo has limited effects on the viability of Drosophila, and animals ectopically expressing Dm-inx3 are unaffected. However, ectopic expression of both transcripts together severely reduces viability, presumably because of the formation of inappropriate gap junctions. We conclude that Dm-Inx2 and Dm-Inx3, which are expressed in overlapping domains during embryogenesis, can form oligomeric gap-junction channels.
authors.affiliation: Sussex Centre for Neuroscience, School of Biological Sciences, University of Sussex, Brighton, BN1 9QG, United Kingdom. l.a.stebbings@sussex.ac.uk
authors.forename: L A
authors.initials: LA
authors.lastname: Stebbings
authors.forename: M G
authors.initials: MG
authors.lastname: Todman
authors.forename: P
authors.initials: P
authors.lastname: Phelan
authors.forename: J P
authors.initials: JP
authors.lastname: Bacon
authors.forename: J A
authors.initials: JA
authors.lastname: Davies
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017630:Connexins / Q000235:genetics / Q000378:metabolism*; D018076:DNA, Complementary; D004330:Drosophila / Q000196:embryology / Q000235:genetics / Q000378:metabolism; D029721:Drosophila Proteins; D017629:Gap Junctions / Q000378:metabolism*; D015870:Gene Expression; D017344:Genes, Insect; D005807:Genes, Overlapping; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009865:Oocytes; D014176:Protein Biosynthesis; D017434:Protein Structure, Tertiary; D014981:Xenopus
chemical_list: D017630:Connexins; D018076:DNA, Complementary; D029721:Drosophila Proteins; C438564:INX3 protein, Drosophila; D019476:Insect Proteins