At Least One Class I Gene in Restriction Fragment Pattern-Y (Rfp-Y), the SecondMHCGene Cluster in the Chicken, Is Transcribed, Polymorphic, and Shows Divergent Specialization in Antigen Binding Region

Abstract

MHC genes in the chicken are arranged into two genetically independent clusters located on the same chromosome. These are the classical B system and restriction fragment pattern-Y (Rfp-Y), a second cluster of MHC genes identified recently through DNA hybridization. Because small numbers of MHC class I and class II genes are present in both B and Rfp-Y, the two clusters might be the result of duplication of an entire chromosomal segment. We subcloned, sequenced, and analyzed the expression of two class I loci mapping to Rfp-Y to determine whether Rfp-Y should be considered either as a second, classical MHC or as a region containing specialized MHC-like genes, such as class Ib genes. The Rfp-Y genes are highly similar to each other (93%) and to classical class Ia genes (73% with chicken B class I; 49% with HLA-A). One locus is disrupted and unexpressed. The other, YFV, is widely transcribed and polymorphic. Mature YFV protein associated with β2m arrives on the surface of chicken B (RP9) lymphoma cells expressing YFV as an epitope-tagged transgene. Substitutions in the YFV Ag-binding region (ABR) occur at four of the eight highly conserved residues that are essential for binding of peptide-Ag in the class Ia molecules. Therefore, it is unlikely that Ag is bound in the YFV ABR in the manner typical of class Ia molecules. This ABR specialization indicates that even though YFV is polymorphic and widely transcribed, it is, in fact, a class Ib gene, and Rfp-Y is a region containing MHC genes of specialized function.

Aflatoxicosis: Lessons from Toxicity and Responses to Aflatoxin B1 in Poultry

“…For example, MHC class I and class II molecules are necessary for antigen presentation to T lymphocytes and are common to the galliform MHC [229][230][231][232][233][234][235][236][237]. In turkeys and chickens, the MHC is composed of 2 genetically unlinked regions, the B-locus (MHC-B) and Y-locus (MHC-Y), co-located on a single microchromosome (GGA16 or MGA18, respectively) [229][230][231][232][233][234][235][236][237]. Although some genes are well characterized, the functions and expression patterns of many poultry MHC genes are still unknown.…”

The Evolution of the Major Histocompatibility Complex in Birds

“…Rfp-Y genotype is also suspected to affect resistance to another tumor-forming virus called Rous sarcoma (LePage et al 2000). The Rfp-Y has not yet been sequenced, but it can be mapped to the same chromosome as the B complex and is physically separated from the B complex by the nuclear organizing region, a region of frequent recombination (Afanassieff et al 2001).…”

Characterization of the turkey MHC chromosome through genetic and physical mapping

“…Genes related to but distinct from those found in the B-locus including class I and class II ␤ -like genes have been mapped to the Y locus (Miller et al, 1994). Notably present are what appear to be polymorphic non-classical MHC class I genes (Afanassieff et al, 2001). A portion of the chicken Y locus has been sequenced and shown to contain at least one class I-like gene (Rogers et al, 2003).…”