Evolution of T cell receptor genes. Extensive diversity of V beta families in the Mexican axolotl.
We have cloned 36 different rearranged variable regions (V beta) genes encoding the beta-chain of the T cell receptor in an amphibian species, Ambystoma mexicanum (the Mexican axolotl). Eleven different V beta segments were identified, which can be classified into 9 families on the basis of a minimum of 75% nucleotide identity. All the cloned V beta segments have the canonical features of known mammalian and avian V beta, including conserved residues Cys23, Trp34, Arg69, Tyr90, and Cys92. There seems to be a greater genetic distance between the axolotl V beta families than between the different V beta families of any mammalian species examined to date: most of the axolotl V beta s have fewer than 35% identical nucleotides and the less related families (V beta 4 and V beta 8) have no more than 23.2% identity (13.5% at the amino acid level). Despite their great mutual divergence, several axolotl V beta are sequence-related to some mammalian V beta genes, like the human V beta 13 and V beta 20 segments and their murine V beta 8 and V beta 14 homologues. However, the axolotl V beta 8 and V beta 9 families are not significantly related to any other V beta sequence at the nucleotide level and show limited amino acid similarity to mammalian V alpha, V kappa III, or VH sequences. The detection of nine V beta families among 35 randomly cloned V beta segments suggests that the V beta gene repertoire in the axolotl is probably larger than presently estimated.
National Center for Scientific Research, Pierre and Marie Curie University, Paris, France.
J S
JS
Fellah
F
F
Kerfourn
J
J
Charlemagne
D000558:Ambystoma mexicanum / Q000235:genetics* / Q000276:immunology; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D006801:Humans; D008969:Molecular Sequence Data; D010802:Phylogeny; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid
D016693:Receptors, Antigen, T-Cell, alpha-beta