14 - The structure and organization of immunoglobulin genes in lower vertebrates

Abstract

There is a major variation in the organization of immunoglobulin (Ig) gene loci among different taxa. The genetic elements and recombination mechanisms that promote the formation of an antigen-combining site, capable of expressing multiple specificities, are highly conserved. This chapter focuses on the structure and organization of Ig genes in non-mammalian vertebrate species, with emphasis on the coldblooded vertebrates. It also describes the remarkable conservation of recombining segmental elements that typifies Ig gene structure and organization in the extant jawed vertebrates. There are at least four major Ig heavy chain gene organizational motifs, demonstrated by studies of divergent vertebrate species—sharing homologous variable (V) and constant (C) region elements and highly conserved recombination signal sequences (RSSs). The similarities and differences among Ig genes of species representing divergent points in vertebrate evolution are also outlined. The molecular genetics of antigen-binding molecules, such as Igs and T cell antigen receptors (TCRs) from widely divergent species have important implications in understanding the overall nature and developmental regulation of adaptive immunity.