Extensive diversity of transcribed TCR-beta in phylogenetically primitive vertebrate

Abstract

The genetic complexity of the expressed TCR Vbeta repertoire in Heterodontus francisci, the horned shark, a member of the most phylogenetically primitive vertebrate class in which TCR genes have been identified, is addressed. The sequences of 55 spleen cDNA clones encoding TCR-beta genes are compared, and 7 diverse Vbeta families are defined by overall sequence identity and clustering based on phylogenetic distance analyses. At least 18 putative Jbeta sequence types, as well as a consensus diversity (D) element that resembles most closely mammalian TCR Dbeta, can he recognized. Extensive sequence diversity, as well as characteristic TCR-beta length variation in CDR3, is evident. Unlike Ig genes in this species, TCR-beta genes exhibit considerable V family multiplicity and appear to utilize combinatorial mechanisms in the generation of immunologic diversity. in this sense, the TCR-beta genes in this cartilaginous fish and humans are more similar than are the genes encoding Ab proteins in these species.