A physical map of a BAC clone contig covering the entire autosome insertion between ovine MHC Class IIa and IIb

Abstract

BackgroundThe ovine Major Histocompatibility Complex (MHC) harbors genes involved in overall resistance/susceptibility of the host to infectious diseases. Compared to human and mouse, the ovine MHC is interrupted by a large piece of autosome insertion via a hypothetical chromosome inversion that constitutes ~25% of ovine chromosome 20. The evolutionary consequence of such an inversion and an insertion (inversion/insertion) in relation to MHC function remains unknown. We previously constructed a BAC clone physical map for the ovine MHC exclusive of the insertion region. Here we report the construction of a high-density physical map covering the autosome insertion in order to address the question of what the inversion/insertion had to do with ruminants during the MHC evolution.ResultsA total of 119 pairs of comparative bovine oligo primers were utilized to screen an ovine BAC library for positive clones and the orders and overlapping relationships of the identified clones were determined by DNA fingerprinting, BAC-end sequencing, and sequence-specific PCR. A total of 368 positive BAC clones were identified and 108 of the effective clones were ordered into an overlapping BAC contig to cover the consensus region between ovine MHC class IIa and IIb. Therefore, a continuous physical map covering the entire ovine autosome inversion/insertion region was successfully constructed. The map confirmed the bovine sequence assembly for the same homologous region. The DNA sequences of 185 BAC-ends have been deposited into NCBI database with the access numbers HR309252 through HR309068, corresponding to dbGSS ID 30164010 through 30163826.ConclusionsWe have constructed a high-density BAC clone physical map for the ovine autosome inversion/insertion between the MHC class IIa and IIb. The entire ovine MHC region is now fully covered by a continuous BAC clone contig. The physical map we generated will facilitate MHC functional studies in the ovine, as well as the comparative MHC evolution in ruminants.

Organization of the Addax Major Histocompatibility Complex Provides Insights Into Ruminant Evolution

“…This hypothesis of ancestral chromosome rearrangement in ruminants has been supported by previous studies comparing the MHC sequences of cattle and sheep with those of nonruminants (such as humans, chimpanzees, and mice) (11,58). Considering that subfamily Hippotraginae is phylogenetically most distant from subfamily Caprinae Bovinae in the family Bovidae ( Figure S7), our results proposed that, at least in the Bovidae, an inversion in the MHC class II region divided the MHC class II region into two discontinuous subregions.…”

“…The genomic organization of MHC in mammals is relatively conserved, with a basic orientation of class I, class III, and class II (9). However, distinct from other animals, the MHC class II region in sheep and cattle is composed of two discontinuous regions, class IIa and class IIb, which result from a substantial autosome inversion (10,11). Recent studies have indicated that this chromosome inversion was also found in the Yangtze porpoise, killer whale, and seven other cetaceans (12,13).…”

Beyond mice and men: environmental change, immunity and infections in wild ungulates

“…(2) MHC organization and usage have noticeable difference from humans. Bovids have an MHC gene organization not seen in other mammals whereby the class II region of the MHC is divided into MHC IIa and MHC IIb regions (148,149). Further, domestic cattle can often express 1-6 different MHC genes, demonstrating plasticity in MHC expression (150).…”

Sequencing and comparative analysis of the gorilla MHC genomic sequence

“…Until now, in no other higher primate has the MHC been sequenced and analysed to the same depth as the human, so this study of such a close ancestor should prove a valuable resource that can be expected to advance our understanding of the structure, function, variation and evolution of this complex region in primates. It also adds to the growing body of data on MHC genes and regions (74) in vertebrates in general (75–78). …”