CHARACTERIZATION OF VARIATION OF RECOMBINATION IN THE HUMAN MHC

人类主要组织相容性复合体(MHC)中的重组被认为在不同的HLA基因座上产生了新的等位基因。它也是在单倍型水平上观察到的多样性的原因，尽管这一活动的功能后果尚不清楚。我们实验室对重组的历史和家族研究提供了整个MHC的重组分数(Q)的估计，并确定了II类区域中潜在的重组热点。人类MHC中的其他重组特征，如重组频率的单倍型特异性和重组所涉及的局部序列基序，也被考虑过，但由于人类群体研究的限制，很难解决。单精子分型有望克服人类群体重组研究中固有的一些局限性。我们使用这项技术对两个标记D6S439和MOGCA进行了分型，这两个标记位于围绕人类MHC的约7Mb区域的两侧。到目前为止，来自12个捐赠者的大约26,000个精子已经成功地对这些标志物进行了分型，捐赠者之间的重组频率范围为1.72%到6.5%。重组频率的单倍型特异性和MHC外多态基因的影响正在使用精子分型技术在两组同卵双胞胎和共享0、1或2 MHC单倍型的兄弟身上进行测试。同时考虑重组分数和连锁不平衡(Ld)的研究可能对MHC连锁群的保护提供意义，无论是选择的还是巧合的。Ld是两个连锁座位上等位基因的非随机关联。在MHC上存在很强的LD，特别是在特定多位点单倍型的等位基因之间和复合体内特定基因之间。LD是对历史事件的测量，在某些情况下可能反映选择压力，而对重组染色体的研究基本上是测量实时事件，这不太可能反映长期的选择过程。例如，从观察到强ld的一对基因之间的重组热点的合理结论是，存在由这些或邻近基因的等位基因组成的单倍型的选择。因此，在重组数据(即遗传距离)的背景下分析LD统计数据可能是识别导致某些单倍型保留的潜在选择压力的有力工具。我们最近完成了MHC内部和侧翼的30个标记的分子分型。对这30个标记之间的LD的初步分析表明，总体上，全球不平衡(Wn)值随着物理图谱距离的增加而减小。此外，分隔约100kb的一对基因座的Wn值范围非常宽，正如在人类白细胞抗原II类区域中清楚地说明的那样。这些数据符合这样一个概念，即不平衡和距离之间的单调关系并不一定发生在小的基因组片段中，在这些片段中，漂移、突变和混合等因素可能会克服重组的影响。我们已经在分离TAP1和TAP2的21kb区域确定了一个重组热点，目前正在对该区域内8个变异位点之间的连锁不平衡进行详细的分析。数据的另一个显著特征是，在多对相隔超过1Mb的标记之间存在显著水平的ID。对这些数据的进一步分析正在进行中。-连锁不平衡、主要组织相容性复合体、重组、单精子分型-人体组织、体液、细胞等

Recombination in the human major histocompatibility complex (MHC) is thought to have played a role in generation of novel alleles at various HLA loci. It is also responsible for the diversity observed at the haplotype level, although the functional consequences of this activity are not clear. Historic and family studies of recombination in our laboratory have provided estimations of recombination fractions (q) across the MHC and identified potential hotspots for recombination in the class II region. Other characteristics of recombination in the human MHC such as haplotype-specificity in recombination frequency and localized sequence motifs involved in recombination have been considered, but have been difficult to address given the constraints of human population studies. Single-sperm typing holds promise in overcoming some of the limitations inherent in the study of recombination in human populations. We have used this technique to type two markers, D6S439 and MOGCA, which flank a region of about 7 Mb encompassing the human MHC. To date, about 26,000 sperm from twelve donors have been typed successfully for these markers and the range of recombination frequencies among donors is 1.72% to 6.5%. Haplotype specificity of recombination frequency and the influence of polymorphic genes outside of the MHC are being tested using the sperm typing technique on samples from two sets of identical twins, and brothers that share 0, 1, or 2 MHC haplotypes. Studies that take into account both recombination fractions and linkage disequilibrium (ld) may provide meaning to conservation of the MHC linkage group, whether selected or coincidental. Ld is the nonrandom association of alleles at two linked loci. Strong ld across the MHC exists, particularly among alleles of specific multi-locus haplotypes and between particular genes within the complex. Ld is a measurement of historical events that may reflect selective pressures in some cases, whereas studies of recombinant chromosomes essentially measure real-time events, which are unlikely to reflect the protracted process of selection. For example, a reasonable conclusion from the observation of a hotspot for recombination in the region between a pair of genes that are in strong ld is that there has been selection for haplotypes composed of alleles at those or neighboring genes. Thus, analysis of ld statistics in the context of recombination data (i.e. genetic distance) could be a powerful tool for identification of potential selective pressures resulting in retention of certain haplotypes. We have recently completed molecular typing of 30 markers within and flanking the MHC. Preliminary analysis of ld between pairs of these 30 markers has indicated that, in general, global disequilibrium (Wn) values decrease with increasing physical map distance. Further, the range of Wn values for pairs of loci separated by about 100 Kb is exceedingly wide range, as is clearly illustrated in the HLA class II region. The data conform to the concept that a monotonic relationship between disequilibrium and distance does not necessarily occur in small genomic segments where factors such as drift, mutation, and admixture may overcome the effect of recombination. We have identified a hotspot for recombination in the 21 Kb region separating TAP1 from TAP2 and a detailed analysis of linkage disequilibrium between eight sites of variation within this region is currently being investigated. Another notable feature of the data is that significant levels of ld exist between many pairs of markers that are separated by more than 1Mb. Further analyses of these data are ongoing. - linkage disequilibrium, Major histocompatibility Complex, recombination, single sperm typing, - Human Tissues, Fluids, Cells, etc.