Kulski Jerzy K, Suzuki Shingo, Shiina Takashi
Faculty of Health and Medical Sciences, The University of Western Australia, Crawley, WA, Australia.
Department of Molecular Life Sciences, Division of Basic Medical Science and Molecular Medicine, Tokai University School of Medicine, Isehara, Japan.
Front Genet. 2021 May 28;12:665899. doi: 10.3389/fgene.2021.665899. eCollection 2021.
The major histocompatibility complex (MHC) on chromosome 6p21 is one of the most single-nucleotide polymorphism (SNP)-dense regions of the human genome and a prime model for the study and understanding of conserved sequence polymorphisms and structural diversity of ancestral haplotypes/conserved extended haplotypes. This study aimed to follow up on a previous analysis of the MHC class I region by using the same set of 95 MHC haplotype sequences downloaded from a publicly available BioProject database at the National Center for Biotechnology Information to identify and characterize the polymorphic class II genes, the pseudogene alleles, the indels of transposable elements as haplotypic lineage markers, and SNP-density crossover (XO) loci at haplotype junctions in DNA sequence alignments of different haplotypes across the extended class II region (∼1 Mb) from the telomeric gene in class III to the gene at the centromeric end of class II. We identified 42 haplotypic indels (20 Alu, 7 SVA, 13 LTR or MERs, and 2 indels composed of a mosaic of different transposable elements) linked to particular HLA-class II alleles. Comparative sequence analyses of 136 haplotype pairs revealed 98 unique XO sites between SNP-poor and SNP-rich genomic segments with considerable haplotype shuffling located in the proximity of putative recombination hotspots. The majority of XO sites occurred across various regions including in the vicinity of between and , between and , between and , and between and , where most XOs were within a sequence. We also determined the genomic positions of the PRDM9-recombination suppression sequence motif and the PRDM9 recombination activation partial binding motif in the class II region of the human reference genome (NC_ 000006) relative to published meiotic recombination positions. Both the recombination and anti-recombination PRDM9 binding motifs were widely distributed throughout the class II genomic regions with 50% or more found within repeat elements; the anti-recombination motifs were found mostly in L1 fragmented repeats. This study shows substantial haplotype shuffling between different polymorphic blocks and confirms the presence of numerous putative ancestral recombination sites across the class II region between various HLA class II genes.
位于6号染色体短臂21区的主要组织相容性复合体(MHC)是人类基因组中单个核苷酸多态性(SNP)密度最高的区域之一,也是研究和理解祖先单倍型/保守延伸单倍型的保守序列多态性和结构多样性的主要模型。本研究旨在通过使用从美国国立生物技术信息中心公开的生物项目数据库下载的同一组95个MHC单倍型序列,对先前MHC I类区域的分析进行跟进,以识别和表征多态性II类基因、假基因等位基因、作为单倍型谱系标记的转座元件插入缺失,以及在从III类端粒基因到II类着丝粒端基因的扩展II类区域(约1 Mb)中不同单倍型的DNA序列比对中,单倍型连接处的SNP密度交叉(XO)位点。我们鉴定出42个与特定HLA-II类等位基因相关的单倍型插入缺失(20个Alu、7个SVA、13个LTR或MERs,以及2个由不同转座元件镶嵌组成的插入缺失)。对136个单倍型对的比较序列分析揭示了98个独特的XO位点,这些位点位于SNP贫乏和SNP丰富的基因组片段之间,在假定的重组热点附近有相当多的单倍型改组。大多数XO位点出现在各个区域,包括在 和 之间、在 和 之间、在 和 之间以及在 和 之间的附近,其中大多数XO位于一个 序列内。我们还确定了人类参考基因组(NC_000006)II类区域中PRDM9重组抑制序列基序和PRDM9重组激活部分结合基序相对于已发表的减数分裂重组位置的基因组位置。重组和抗重组PRDM9结合基序在整个II类基因组区域广泛分布,50%或更多位于重复元件内;抗重组基序大多在L1片段化重复序列中发现。这项研究表明不同多态性模块之间存在大量单倍型改组,并证实了在各种HLA-II类基因之间的II类区域存在大量假定的祖先重组位点。