The properties of the single chicken MHC classical class II ? chain (B-LA) gene indicate an ancient origin for the DR/E-like isotype of class II molecules

Abstract

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.

Chicken CD1 genes are located in the MHC: CD1 and endothelial protein C receptor genes constitute a distinct subfamily of class-I-like genes that predates the emergence of mammals

“…Because histone H3 has been localized to the MHC (Kaufman et al 1999b), these results provide convincing evidence that, unlike human and mouse CD1 genes, chicken CD1 genes are located adjacent to the class I (BF) and IIB (BLB) genes and thus encoded within the MHC B system. Orientation of the cosmid cluster (AL023516.1) relative to the previously characterized class IIA gene (BLA) (Kaufman et al 1995;Salomonsen et al 2003) indicates that the CD1 genes map between BF and BLA. To independently test the physical linkage of CD1 to the MHC, we performed dual-color FISH using chicken tapasin cDNA and a mixture of chicken CD1.1 and CD1.2 cDNA as probes (Fig.…”

Different Evolutionary Histories of the Two Classical Class I Genes BF1 and BF2 Illustrate Drift and Selection within the Stable MHC Haplotypes of Chickens

“…Genomic DNA from seven inbred lines of chickens with defined MHC type (line 6 1 (B2), line C-B4 (B4), line C-B12 (B12), line WL (B14), line 15I 5 (B15), line P2a (B19), line N (B21)) were digested with EcoRV and NotI, and Southern blots were performed as described, washing with 0.2ϫ SSC (30,31). The 550-bp DMB2 probe was produced by cutting a DMB2 genomic clone (derived from line 6 1 DNA by PCR, Ref.…”

Two CD1 genes map to the chicken MHC, indicating that CD1 genes are ancient and likely to have been present in the primordial MHC

“…However, the simplest interpretation of the data in this paper is that the CD1 and class I and II genes arose in the primordial MHC and were originally all present in the paralogous regions, with subsequent deletion of the CD1 genes from the mammalian MHC and , and 1 min at 72°C, and twice purified by agarose gel electrophoresis. Southern blots were performed as described (26,27), with washing at low stringency (2ϫ SSC at 65°C for 30 min). Lines WL, 15I 5 (28) were used for mapping as described (27).…”