Das P J, Chowdhary B P, Raudsepp T
Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX 77843-4458, USA.
Cytogenet Genome Res. 2009;126(1-2):139-47. doi: 10.1159/000245913. Epub 2009 Dec 9.
The pseudoautosomal region (PAR) is a small region of sequence homology between mammalian X and Y chromosomes and is needed for sex chromosome segregation in male meiosis. The region, though studied as yet in only a few species, shows considerable variation in size and gene content. We have constructed a medium-density gene map for the cattle PAR and the adjacent X-specific region by isolating and mapping 18 BAC clones which contain 20 PAR- and 5 X-specific genes. One BAC clone containing TBL1XY and GPR143 spanned the recently demarcated bovine pseudoautosomal boundary (PAB). Comparing the gene map of cattle PAR with the high-resolution maps of human, horse, and dog PAR allowed to estimate that the size of cattle PAR is approximately 5-9 Mb. BAC end sequence analysis showed that there is a gradient of decreasing GC content from PARter towards the PAB which is consistent with findings in human, mouse, and horse. The 20 PAR- and 5 X-specific cattle genes were mapped also in goat and sheep, showing that PAR in the 3 species is similar in size, gene content, and gene order. For the first time the PAB was determined in goat sex chromosomes. Comparison of cattle, goat, and sheep PAR with homologous regions on human and horse X chromosomes showed a high degree of linkage conservation between all species. However, the most terminal human, horse, and dog PAR gene, PLCXD1, is X-specific in ruminants. Since the human/horse linkage group containing PLCXD1 is of ancestral origin, the location of PLCXD1 can be considered as a de novo event in ruminant sex chromosome evolution. The gene map of the cattle PAR adds to our knowledge about the comparative organization and evolution of the eutherian PAR and aids the sequencing, sequence assembly, and annotation of the terminal region of BTAXq.
假常染色体区域（PAR）是哺乳动物X和Y染色体之间的一小段序列同源区域，是雄性减数分裂中性染色体分离所必需的。该区域虽然目前仅在少数物种中进行了研究，但在大小和基因含量上表现出相当大的差异。我们通过分离和定位18个BAC克隆构建了牛PAR及相邻X特异性区域的中密度基因图谱，这些克隆包含20个PAR特异性基因和5个X特异性基因。一个包含TBL1XY和GPR143的BAC克隆跨越了最近划定的牛假常染色体边界（PAB）。将牛PAR的基因图谱与人类（智人）、马和犬PAR的高分辨率图谱进行比较，估计牛PAR的大小约为5-9 Mb。BAC末端序列分析表明，从PAR末端向PAB方向GC含量呈递减梯度，这与人类、小鼠和马的研究结果一致。这20个PAR特异性基因和5个X特异性牛基因也定位在了山羊和绵羊中，表明这三个物种的PAR在大小、基因含量和基因顺序上相似。首次在山羊性染色体中确定了PAB。将牛、山羊和绵羊的PAR与人类和马X染色体上的同源区域进行比较，结果表明所有物种之间都有高度的连锁保守性。然而，人类、马和犬PAR最末端的基因PLCXD1在反刍动物中却是X特异性的。由于包含PLCXD1的人类/马连锁群起源于祖先，因此PLCXD1的定位可被视为反刍动物性染色体进化中的一个从头事件。牛PAR的基因图谱增加了我们对真兽亚纲PAR的比较组织和进化的了解，并有助于牛X染色体（BTAXq）末端区域的测序、序列组装和注释。
