Origin of immunoglobulins and T cell receptors: A candidate gene for invasion by the RAG transposon.

ABSTRACT: Rearranging antigen receptors (AgRs) arose when a variable (V) domain exon was invaded by the recombination-activating gene (RAG) transposon ~500 million years ago. We show here that the elasmobranch immunoglobulin heavy (IgH) isotypes-IgM, IgW, and IgNAR-are linked near the αδ T cell receptor (TCRαδ) locus. This linkage presages the emergence of the osteichthyan IgH translocon arrangement and clarifies the relationship between IgH and TCRδs. Recently, we reported UrIg, a nonrearranging, elasmobranch major histocompatibility complex (MHC)-linked AgR gene. Here, we describe a nonrearranging UrIg paralogue, UrIg2, linked to this IgM/IgNAR/IgW/TCRαδ gene cluster in an AgR complex (AgRC). UrIg2 amino-terminal domains make homodimers where the C2-C3 structure resembles IgGF

SUBMITTER: Flajnik MF 

PROVIDER: S-EPMC12227049 | biostudies-literature | 2025 Jul

REPOSITORIES: biostudies-literature