Evolutionary Genomics of Immunoglobulin-Encoding Loci in Vertebrates

Sabyasachi Das, Masayuki Hirano, Rea Tako, Chelsea McCallister, Nikolas Nikolaidis

Abstract

Immunoglobulins (or antibodies) are an essential element of the jawed vertebrate adaptive immune response system. These molecules have evolved over the past 500 million years and generated highly specialized proteins that recognize an extraordinarily large number of diverse substances, collectively known as antigens. During vertebrate evolution the diversification of the immunoglobulin-encoding loci resulted in differences in the genomic organization, gene content, and ratio of functional genes and pseudogenes. The tinkering process in the immunoglobulin-encoding loci often gave rise to lineage-specific characteristics that were formed by selection to increase species adaptation and fitness. Immunoglobulin loci and their encoded antibodies have been shaped repeatedly by contrasting evolutionary forces, either to conserve the prototypic structure and mechanism of action or to generate alternative and diversified structures and modes of function. Moreover, evolution favored the development of multiple mechanisms of primary and secondary antibody diversification, which are used by different species to effectively generate an almost infinite collection of diverse antibody types. This review summarizes our current knowledge on the genomics and evolution of the immunoglobulinencoding loci and their protein products in jawed vertebrates.

Keywords: Antibodies, gnathostomes, genomic organization, cladistic markers, microRNA, comparative genomics, evolution, jawed vertebrates, IgH-Encoding Loci, Somatic Hypermutation