The properties of the single chicken MHC classical class II alpha chain ( B-LA) gene indicate an ancient origin for the DR/E-like isotype of class II molecules.
In mammals, there are MHC class II molecules with distinctive sequence features, such as the classical isotypes DR, DQ and DP. These particular isotypes have not been reported in non-mammalian vertebrates. We have isolated the class II (B-L) alpha chain from outbred chickens as the basis for the cloning and sequencing of the cDNA. We found only one class II alpha chain transcript, which bears the major features of a classical class II alpha sequence, including the critical peptide-binding residues. The chicken sequence is more similar to human DR than to the DQ, DP, DO or DM isotypes, most significantly in the peptide-binding alpha(1) domain. The cDNA and genomic DNA sequences from chickens of diverse origins show few alleles, which differ in only four nucleotides and one amino acid. In contrast, significant restriction fragment length polymorphism is detected by Southern blot analysis of genomic DNA, suggesting considerable diversity around the gene. Analysis of a large back-cross family indicates that the class II alpha chain locus ( B-LA) is located roughly 5.6 cM from the MHC locus, which encodes the classical class II beta chains. Thus the chicken class II alpha chain gene is like the mammalian DR and E isotypes in three properties: the presence of the critical peptide-binding residues, the low level of polymorphism and sequence diversity, and the recombinational separation from the class II beta chain genes. These results indicate that the sequence features of this lineage are both functionally important and at least 300 million years old.
Salomonsen
Jan
J
Department of Virology and Immunology, Royal Veterinary and Agricultural University, Stigbøjlen 7, C 1870, Frederiksberg, Denmark.
Marston
Denise
D
Avila
David
D
Bumstead
Nat
N
Johansson
Brit
B
Juul-Madsen
Helle
H
Olesen
Gerda D
GD
Riegert
Patricia
P
Skjødt
Karsten
K
Vainio
Olli
O
Wiles
Michael V
MV
Kaufman
Jim
J
D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D015139:Blotting, Southern; D002645:Chickens / Q000235:genetics* / Q000276:immunology; D002875:Chromosomes / Q000235:genetics; D003001:Cloning, Molecular; D018076:DNA, Complementary; D005091:Exons; D005260:Female; D005802:Genes, MHC Class II; D006682:HLA-DP Antigens / Q000235:genetics; D006683:HLA-DQ Antigens / Q000235:genetics; D006684:HLA-DR Antigens / Q000235:genetics; D006239:Haplotypes; D007438:Introns; D008297:Male; D018895:Microsatellite Repeats; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid
D018076:DNA, Complementary; D006682:HLA-DP Antigens; D006683:HLA-DQ Antigens; D006684:HLA-DR Antigens