Evolutionary selection pressure and family relationships among connexin genes

Abstract

AbstractWe suggest an extension ofconnexinorthology relationships across the major vertebrate lineages. We first show that the conserved domains of mammalianconnexins(encoding the N-terminus, four transmembrane domains and two extracellular loops) are subjected to a considerably more strict selection pressure than the full-length sequences or the variable domains (the intracellular loop and C-terminal tail). Therefore, the conserved domains are more useful for the study of family relationships over larger evolutionary distances. The conserved domains ofconnexinswere collected from chicken,Xenopus tropicalis, zebrafish, pufferfish, green spotted pufferfish,Ciona intestinalisandHalocynthia pyriformis(two tunicates). A total of 305connexinsequences were included in this analysis. Phylogenetic trees were constructed, from which the orthologies and the presumed evolutionary relationships between the sequences were deduced. The tunicateconnexinsstudied had the closest, but still distant, relationships to vertebrateconnexin36,39.2,43.4,45and47. The main structure in theconnexinfamily known from mammals pre-dates the divergence of bony fishes, but some additional losses and gains ofconnexinsequences have occurred in the evolutionary lineages of subsequent vertebrates. Thus, theconnexingene family probably originated in the early evolution of chordates, and underwent major restructuring with regard to gene and subfamily structures (including the number of genes in each subfamily) during early vertebrate evolution.