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C1 inhibitor (C1IN) is a multi-facet serine protease inhibitor in the plasma cascades, inhibiting several proteases, notably, regulates both complement and contact system activation. Despite huge advancements in the understanding of C1IN based on biochemical properties and its roles in the plasma cascades, the phylogenetic history of C1IN remains uncharacterized. To date, there is no comprehensive study illustrating the phylogenetic history of C1IN. Herein, we explored phylogenetic history of C1IN gene in vertebrates. Fishes have C1IN with two immunoglobulin like domains attached in the N-terminal region. The RCL regions of CIIN from fishes and tetrapod genomes have variations at the positions P2 and P1'. Gene structures of C1IN gene from selected ray-finned fishes varied in the Ig domain region with creation of novel intron splitting exon Im2 into Im2a and Im2b. This intron is limited to ray-finned fishes with genome size reduced below 1 Gb. Hence, we suggest that genome compaction and associated double-strand break repairs are behind this intron gain. This study reveals the evolutionary history of C1IN and confirmed that this gene remains the same locus for ∼450 MY in 52 vertebrates analysed, but it is not found in frogs and lampreys., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Highlights: [•] ATIII possesses additional intron 262c is maintained in ray-finned fishes, but lost in other vertebrates. [•] ATIII is maintained in same genomic loci with few changes in fishes. [•] ATIII has 1997 variants in 1092 human genomes from 14 populations. [•] Three top variation classes are 76.2% SNPs, 11.8% deletions and 8.1% insertions. [•] There are 63 missense variants of human ATIII causes change in amino acids. [ABSTRACT FROM AUTHOR]