| 总结: | <p>Abstract</p> <p>Background</p> <p>The quail and chicken major histocompatibility complex (<it>Mhc</it>) genomic regions have a similar overall organization but differ markedly in that the quail has an expanded number of duplicated class I, class IIB, natural killer (NK)-receptor-like, lectin-like and BG genes. Therefore, the elucidation of genetic factors that contribute to the greater <it>Mhc </it>diversity in the quail would help to establish it as a model experimental animal in the investigation of avian <it>Mhc </it>associated diseases.</p> <p>Aims and approaches</p> <p>The main aim here was to characterize the genetic and genomic features of the transcribed major quail <it>MhcIIB </it>(<it>CojaIIB</it>) region that is located between the <it>Tapasin </it>and <it>BRD2 </it>genes, and to compare our findings to the available information for the chicken <it>MhcIIB </it>(<it>BLB</it>). We used four approaches in the study of the quail <it>MhcIIB </it>region, (1) haplotype analyses with polymorphic loci, (2) cloning and sequencing of the RT-PCR <it>CojaIIB </it>products from individuals with different haplotypes, (3) genomic sequencing of the <it>CojaIIB </it>region from the individuals with the different haplotypes, and (4) phylogenetic and duplication analysis to explain the variability of the region between the quail and the chicken.</p> <p>Results</p> <p>Our results show that the <it>Tapasin-BRD2 </it>segment of the quail <it>Mhc </it>is highly variable in length and in gene transcription intensity and content. Haplotypic sequences were found to vary in length between 4 to 11 kb. <it>Tapasin-BRD2 </it>segments contain one or two major transcribed <it>CojaIIBs </it>that were probably generated by segmental duplications involving c-type lectin-like genes and NK receptor-like genes, gene fusions between two <it>CojaIIBs </it>and transpositions between the major and minor <it>CojaIIB </it>segments. The relative evolutionary speed for generating the <it>MhcIIBs </it>genomic structures from the ancestral <it>BLB2 </it>was estimated to be two times faster in the quail than in the chicken after their separation from a common ancestor. Four types of genomic rearrangement elements (GRE), composed of simple tandem repeats (STR), were identified in the <it>MhcIIB </it>genomic segment located between the <it>Tapasin-BRD2 </it>genes. The GREs have many more STR numbers in the quail than in the chicken that displays strong linkage disequilibrium.</p> <p>Conclusion</p> <p>This study suggests that the <it>Mhc </it>classIIB region has a flexible genomic structure generated by rearrangement elements and rapid SNP accumulation probably as a consequence of the quail adapting to environmental conditions and pathogens during its migratory history after its divergence from the chicken.</p>
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