This entry includes pannexins from vertebrates and innexins from invertebrate []. Gap junctions are composed of membrane proteins,which form a channel permeable for ions and small molecules connectingcytoplasm of adjacent cells. Although gap junctions provide similar functionsin all multicellular organisms, until recently it was believed thatvertebrates and invertebrates use unrelated proteins for this purpose. Whilethe connexins family of gap junction proteins is well-characterised in vertebrates, no homologues have been found in invertebrates. Inturn, gap junction molecules with no sequence homology to connexins have beenidentified in insects and nematodes. It has been suggested that these proteinsare specific invertebrate gap junctions, and they were thus named innexins(invertebrate analog of connexins) []. As innexin homologues were recently identified in other taxonomic groups including vertebrates, indicating their ubiquitous distribution in the animal kingdom, they were called pannexins(from the Latin pan-all, throughout, and nexus-connection, bond) [, , ].Genomes of vertebrates carry probably a conserved set of 3 pannexin paralogs(PANX1, PANX2 and PANX3). Invertebrate genomes may contain more than a dozenpannexin (innexin) genes. Vinnexins, viral homologues of pannexins/innexins,were identified in Polydnaviruses that occur in obligate symbioticassociations with parasitoid wasps. It was suggested that virally encodedvinnexin proteins may function to alter gap junction proteins in infected hostcells, possibly modifying cell-cell communication during encapsulationresponses in parasitized insects [, ]. Structurally pannexins are simillar to connexins. Both types of proteinconsist of a cytoplasmic N-terminal domain, followed by four transmembranesegments that delimit two extracellular and one cytoplasmic loops; the C-terminal domain is cytoplasmic.
