Fig. 1. The topology of (A) connexins and (B) pannexins (formerly innexins) with four transmembrane (TM) domains and intracellular N and C termini is the same, yet their sequences are not related (C,D). Alignments in C and D are limited to the most conserve regions that include the first two transmembrane domains TM1 and TM2 and the first extracellular loop; for connexins, mammals: human; bony fish, Fugu, ray; tunicate Ascidia (GeneBank accession numbers: P17302, AAL89668 Q92107 and AAQ90187; for pannexins, cnidarian: Hydra; flatworm: Planaria; annelid: leech, nematode; mollusc: Clione; insect, fly; tunicate Ascidia; mammals: human; ichnovirus (accession numbers: BK005478, AF207819, CAD55801 CAA79529 AAF75839 AAA28745 BK005483, AAK91714and AAO45829. (E) Presence (+) or absence (–) of connexins (blue) and pannexins (red) in the main taxonomic groups of multicellular organisms are indicated in simplified phylogenetic tree.