Evolution of variable lymphocyte receptor B antibody loci in jawless vertebrates

Significance Jawless vertebrates, lampreys and hagfish, use three types of variable leucine-rich repeat proteins as antigen receptors: VLRB on B-like cells and VLRA or VLRC on T-like lymphocytes. In their incomplete germline status, the VLRB genes in different lamprey species uniquely possess long noncoding intervening regions, which contain different sets of transposable elements and potential donor cassettes. Phylogenetic analysis of the germline VLR genes reveals ongoing evolution over the last 250 million y. Comparative assessment of genomic sequences in two lamprey species yields a detailed map of their VLRB loci. The use of this map, together with an analysis of cassette usage in a large repertoire of expressed VLRB s, supports a fragmented Lego-like model of VLRB assembly.