Immunoglobulin heavy constant gamma gene evolution is modulated by both the divergent and birth-and-death evolutionary models

Abstract

Immunoglobulin G (IgG) is one of the five antibody classes produced in mammals as part of the humoral responses. This high-affinity antibody produced late in a primary immune response is responsible for protecting the organisms from infection. This proteins heavy chain constant region is encoded by the Ig gamma gene (Ig{gamma}). In Humans, IgG has evolved into four subclasses with specialized effector functions. However, in Platyrrhini, IgG has been reported to be encoded by a single-copy gene. Here, we analyzed data from 38 primate genome sequences to identify Ig{gamma} genes and describe the evolution of this immunoglobulin in this group. Ig{gamma} belongs to a multigene family that evolves by the birth-death evolutionary model in primates. Whereas Strepsirrhini and Platyrrhini have a single-copy gene, in Catarrhini species it has expanded to having several paralogs in their genomes; some have been deleted or have become pseudogenes. Furthermore, episodic positive selection might promote a specialized species-specific IgG effector function. A hypothesis for the Ig{gamma} evolution has been proposed, suggesting that IgG has evolved to reach an optimal number of copies per genome to adapt their humoral immune responses to different environmental conditions. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=105 SRC="FIGDIR/small/456010v1_ufig1.gif" ALT="Figure 1"> View larger version (21K): org.highwire.dtl.DTLVardef@9b9ec3org.highwire.dtl.DTLVardef@d42b16org.highwire.dtl.DTLVardef@158c023org.highwire.dtl.DTLVardef@1ae5117_HPS_FORMAT_FIGEXP M_FIG C_FIG