Raudsepp T, Chowdhary B P
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. 2008;121(2):102-9. doi: 10.1159/000125835. Epub 2008 Jun 9.
The pseudoautosomal region (PAR) is a genomic segment on mammalian sex chromosomes where sequence homology mimics that seen between autosomal homologues. The region is essential for pairing and proper segregation of sex chromosomes during male meiosis. As yet, only human/chimp and mouse PARs have been characterized. The two groups of species differ dramatically in gene content and size of the PAR and therefore do not provide clues about the likely evolution and constitution of PAR among mammals. Here we characterize the equine PAR by i) isolating and arranging 71 BACs containing 129 markers (110 STS and 19 genes) into two contigs spanning the region, ii) precisely localizing the pseudoautosomal boundary (PAB), and iii) describing part of the contiguous X- and Y-specific regions. We also report the discovery of an approximately 200 kb region in the middle of the PAR that is present in the male-specific region of the Y (MSY) as well. Such duplication is a novel observation in mammals. Further, comparison of the equine PAR with the human counterpart shows that despite containing orthologs from an additional 1 Mb region beyond the human PAR1, the equine PAR is around 0.9 Mb smaller than the size of the human PAR. We theorize that the PAR varies in size and gene content across evolutionarily closely as well as distantly related mammals. Although striking differences like those observed between human and mouse may be rare, variations similar to those seen between horse and human may be prevalent among mammals.
假常染色体区域（PAR）是哺乳动物性染色体上的一个基因组片段，其序列同源性类似于常染色体同源物之间的同源性。该区域对于雄性减数分裂过程中性染色体的配对和正确分离至关重要。迄今为止，仅对人类/黑猩猩和小鼠的PAR进行了表征。这两组物种在PAR的基因含量和大小上存在巨大差异，因此无法提供关于哺乳动物PAR可能的进化和组成的线索。在这里，我们通过以下方式对马的PAR进行表征：i）分离并排列71个含有129个标记（110个STS和19个基因）的BAC，形成跨越该区域的两个重叠群；ii）精确确定假常染色体边界（PAB）；iii）描述部分连续的X和Y特异性区域。我们还报告了在PAR中间发现一个约200 kb的区域，该区域也存在于Y染色体的雄性特异性区域（MSY）中。这种重复在哺乳动物中是一个新发现。此外，马的PAR与人类对应物的比较表明，尽管马的PAR包含来自人类PAR1之外额外1 Mb区域的直系同源物，但其大小比人类PAR小约0.9 Mb。我们推测，PAR在进化上密切相关以及远缘相关的哺乳动物中，其大小和基因含量会有所不同。虽然像人类和小鼠之间观察到的显著差异可能很少见，但类似于马和人类之间看到的变化可能在哺乳动物中普遍存在。
