Evolution of the Structure and Organization of the Mammalian Immunoglobulin Loci

Abstract

Abstract There are three extant lineages of mammals: placentals (e.g. humans and mice), marsupials (e.g. kangaroos and opossums), and monotremes (e.g. platypus). Of the three lineages, the marsupials are unusually and uniformly limited in their immunoglobulin heavy chain (IgH) isotype content. All marsupials studied have only one IgM, IgG, IgE, and IgA and lack IgD. Comparatively, there is a greater complexity of IgH isotypes and subclasses in both placentals and monotremes. Marsupials also have a greater complexity in their light (L) chain V genes than IgH chains. Transposable elements (TEs), like retroelements, have been hypothesized to contribute to gene copy variation and genome evolution. Recently, these TEs have been found in the IgH loci. Here we investigate the impact these TEs have on the evolution of marsupial IgH and IgL loci. We have found that some of the TEs in the opossum IgH locus are short and non-functional, potentially contributing to the restriction seen in the locus. Conversely, the TEs in the L chain loci are longer and may explain the differences in complexity in both the V and C regions between the H and L chain loci. Supported by National Science Foundation Award IOS-2103367.