Structure and diversity of the TCR alpha-chain in a teleost fish.
T cell receptor beta-chain genes are well characterized in representatives of most vertebrate phyla, from sharks to mammals, but the molecular structure of complete TCR alpha-chains has not yet been established in cold-blooded vertebrates. We used a PCR approach to isolate cDNAs encoding putative teleost fish (Oncorhynchus mykiss, rainbow trout) TCR alpha-chains. Eight V alpha segments were identified, belonging to six different families, and the best amino acid sequence identity scores for these trout V alpha were all provided by mammalian V alpha or V delta sequences. Twenty-four (60.1 %) of the 39 analyzed V alpha segments belong to the V alpha 2 family, which has limited homology with mammalian V alpha/delta sequences and with the human V pre-B sequence. A total of 32 different J alpha segments were identified from 40 J alpha regions sequenced, suggesting that a large repertoire of J alpha segments is a characteristic of most vertebrates. The structural properties of the TCR alpha-chain complementarity-determining region 3 loop are well conserved between trout and mammals, suggesting that this region has been under continuous selective pressure in jawed vertebrate evolution. The trout C alpha segment has conserved N-terminal and transmembrane domains, but the C alpha intercysteine distance contains only 40 residues, significantly smaller as compared with mammals (49-56 residues). The conserved features of teleost fish TCR beta- and alpha-chains with their mammalian equivalents suggest that TCR-alpha beta receptors were still present in the common Devonian ancestors of modern teleost fish and mammals, about 450 million years ago.
Partula
S
S
Comparative Immunology Group, National Center for Scientific Research, Pierre and Marie Curie University, Paris, France.
de Guerra
A
A
Fellah
J S
JS
Charlemagne
J
J
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D008221:Lymphoid Tissue / Q000737:chemistry; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000276:immunology; D017686:Oncorhynchus mykiss / Q000235:genetics / Q000276:immunology*; D009928:Organ Specificity / Q000235:genetics / Q000276:immunology; D012333:RNA, Messenger / Q000302:isolation & purification; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000737:chemistry* / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D013329:Structure-Activity Relationship
D012333:RNA, Messenger; D016693:Receptors, Antigen, T-Cell, alpha-beta