Abstract
It was previously shown that the connexin gene family had relatively similar subfamily structures in several vertebrate groups. Still, many details were left unclear. There are essentially no data between tunicates, which have connexins that cannot be divided into the classic subfamilies, and teleosts, where the subfamilies are easily recognized. There are also relatively few data for the groups that diverged between the teleosts and mammals. As many of the previously analyzed genomes have been improved, and many more genomes are available, we reanalyzed the connexin gene family and included species from all major vertebrate groups. The major results can be summarized as follows: (i) The same connexin subfamily structures are found in all Gnathostomata (jawed vertebrates), with some variations due to genome duplications, gene duplications and gene losses. (ii) In contrast to previous findings, birds do not have a lower number of connexins than other tetrapods. (iii) The cyclostomes (lampreys and hagfishes) possess genes in the alpha, beta, gamma and delta subfamilies, but only some of the genes show a phylogenetic affinity to specific genes in jawed vertebrates. Thus, two major evolutionary transformations have occurred in this gene family, from tunicates to cyclostomes and from cyclostomes to jawed vertebrates.
Highlights
Connexins are transmembrane proteins that aggregate into hexameric structures called connexons, and connexons from adjacent cells further line up with each other to form a channel that can connect the cytoplasms in the two neighboring cells
The present phylogenetic analyses of the connexin genes include a wider range of vertebrate groups than in previous works [8,9,14,16,17,18]
This work confirms earlier observations of the connexins being divided into alpha, beta, gamma, delta and epsilon subfamilies in mammals, birds and teleosts and extends this to crocodiles, turtles, lizards, the lobe-finned fish Latimeria, ray-finned fishes in general and cartilaginous fishes
Summary
Connexins are transmembrane proteins that aggregate into hexameric structures called connexons, and connexons from adjacent cells further line up with each other to form a channel that can connect the cytoplasms in the two neighboring cells (reviewed by Harris [1]). The channels further aggregate into smaller or larger plaques, called gap junctions, named after the small gap between the neighboring cell membranes, which contrasts with the tight apposition of the membranes in the tight junctions. These channels are regulated by many mechanisms, including numerous cell-signaling systems [2], which may affect the connexins at every stage in their life cycle, from gene expression via the gating of the channels (opening and closing behaviors) to their degradation [1]. Only humans and rodents have received a Greek nomenclature, but as stated by the Zebrafish Nomenclature Conventions:
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