Gene organization of the quail major histocompatibility complex ( MhcCoja ) class I gene region

Abstract

Class I genomic clones of the quail (Coturnix japonica) major histocompatibility complex (MhcCoja) were isolated and characterized. Two clusters spanning the 90.8 kilobase (kb) and 78.2 kb class I gene regions were defined by overlapping cosmid clones and found to contain at least twelve class I loci. However, unlike in the chicken Mhc, no evidence for the existence of any Coja class II gene was obtained in these two clusters. Based on comparative analysis of the genomic sequences with those of the cDNA clones, Coja-A, Coja-B, Coja-C, and Coja-D (Shiina et al. 1999), these twelve loci were assigned to represent one Coja-A gene, two Coja-B genes (Coja-B1 and -B2), four Coja-C genes (Coja-C1-C4), four Coja-D genes (Coja-D1-D4), and one new Coja-E gene. A class I gene-rich segment of 24.6 kb in which five of these genes (Coja-B1, -B2, -D1, -D2 and -E) are densely packed were sequenced by the shotgun strategy. All of these five class I genes are very compact in size [2089 base pairs (bp)-2732 bp] and contain no apparent genetic defect for functional expression. A transporter associated with the antigen processing (TAP) gene was identified in this class I gene-rich segment. These results suggest that the quail class I region is physically separated from the class II region and characterized by a large number of the expressible class I loci (at least seven) in contrast to the chicken Mhc, where the class I and class II regions are not clearly differentiated and only at most three expressed class I loci so far have been recognized.

An Mhc Component to Kin Recognition and Mate Choice in Birds: Predictions, Progress, and Prospects

“…The B complex of chickens has been termed "minimal essential" because of both its structural and functional minimalism; chickens express strongly only one class I and II gene, whereas other Mhc genes are either nonpolymorphic or expressed at low levels (Kaufman et al 1999b). The Mhc of Japanese quail is the best-characterized avian system aside from chickens and contains more Mhc genes and an increased number of duplicated non-Mhc genes than does the chicken B complex (Shiina et al 1999). Two Mhc class II genes have been discovered in the ring-necked pheasant (Wittzell et al 1999a), and there is a second region containing Mhc genes that may be homologous to the chicken Rfp-Y.…”

“…Recent years have seen the complete sequencing of the chicken and Japanese quail (Coturnix japonica) Mhc regions (Kaufman et al 1999a;Shiina et al 1999 (Meager and Potts 1997;Paterson et al 1998), particularly in light of the fact that Mhc genes are now known to undergo extensive concerted evolution (Edwards et al 1995;Wittzell et al 1999a). Concerted evolution is a molecular process whereby different genes within a species exchange sequence information, by gene conversion or other mechanisms.…”

Comparative Genomic Analysis of Two Avian (Quail and Chicken) MHC Regions

“…This difference in immunotolerance in xenotransplantation may be explained by a greater capacity of the Mhc repertoire in the quail than the chicken to become tolerant to Ags presented peripherally from the early developmental stages (22). Our genomic analyses have previously revealed the presence of many more Mhc class I and class IIB genes in the quail genome than in the chicken genome (23,24). For example, the quail was found to encode at least 12 Mhc class I loci with the gene products for at least four of these loci possibly serving as ligands to TCRs (23,25,26).…”

“…Our genomic analyses have previously revealed the presence of many more Mhc class I and class IIB genes in the quail genome than in the chicken genome (23,24). For example, the quail was found to encode at least 12 Mhc class I loci with the gene products for at least four of these loci possibly serving as ligands to TCRs (23,25,26). Therefore, the different outcomes of xenogenetic transplantation between chicken and quail may be attributed in part to the differences in the number of expressed MHC loci and the associated capacity for Ag presentation.…”

Extensive Allelic Diversity of MHC Class I in Wild Mallard Ducks

“…For example, Japanese quail have a series of duplications yielding seven MHC class I genes and at least four expressed genes (although only two appear to be classical class I MHC) (23)(24)(25). However, the Inoko group has since published that only one of these two expressed classical loci is highly expressed (26), much like the chicken.…”