The Davies Research Centre, School of Animal and Veterinary Sciences, University of Adelaide, Roseworthy, South Australia, Australia.
Genome Informatics Section, Computational and Statistical Genomics Branch, National Human Genome Research Institute, Bethesda, MD, USA.
BMC Genomics. 2019 Dec 19;20(1):1000. doi: 10.1186/s12864-019-6364-z.
Mammalian X chromosomes are mainly euchromatic with a similar size and structure among species whereas Y chromosomes are smaller, have undergone substantial evolutionary changes and accumulated male specific genes and genes involved in sex determination. The pseudoautosomal region (PAR) is conserved on the X and Y and pair during meiosis. The structure, evolution and function of mammalian sex chromosomes, particularly the Y chromsome, is still poorly understood because few species have high quality sex chromosome assemblies.
Here we report the first bovine sex chromosome assemblies that include the complete PAR spanning 6.84 Mb and three Y chromosome X-degenerate (X-d) regions. The PAR comprises 31 genes, including genes that are missing from the X chromosome in current cattle, sheep and goat reference genomes. Twenty-nine PAR genes are single-copy genes and two are multi-copy gene families, OBP, which has 3 copies and BDA20, which has 4 copies. The Y chromosome X-d1, 2a and 2b regions contain 11, 2 and 2 gametologs, respectively.
The ruminant PAR comprises 31 genes and is similar to the PAR of pig and dog but extends further than those of human and horse. Differences in the pseudoautosomal boundaries are consistent with evolutionary divergence times. A bovidae-specific expansion of members of the lipocalin gene family in the PAR reported here, may affect immune-modulation and anti-inflammatory responses in ruminants. Comparison of the X-d regions of Y chromosomes across species revealed that five of the X-Y gametologs, which are known to be global regulators of gene activity and candidate sexual dimorphism genes, are conserved.
哺乳动物的 X 染色体主要是常染色体，在物种间具有相似的大小和结构，而 Y 染色体较小，经历了大量的进化变化，并积累了雄性特异性基因和性别决定相关基因。假常染色体区 (PAR) 在 X 和 Y 染色体上是保守的，在减数分裂过程中配对。哺乳动物性染色体，特别是 Y 染色体的结构、进化和功能仍知之甚少，因为很少有物种具有高质量的性染色体组装。
我们在这里报告了第一个牛的性染色体组装，包括跨越 6.84Mb 的完整 PAR 和三个 Y 染色体 X 退化（X-d）区域。PAR 包含 31 个基因，包括当前牛、绵羊和山羊参考基因组中缺失的 X 染色体基因。PAR 中有 29 个基因是单拷贝基因，两个是多拷贝基因家族，OBP 有 3 个拷贝，BDA20 有 4 个拷贝。Y 染色体 X-d1、2a 和 2b 区域分别包含 11、2 和 2 个配子体。
反刍动物 PAR 包含 31 个基因，与猪和狗的 PAR 相似，但比人类和马的 PAR 更长。假常染色体边界的差异与进化分歧时间一致。我们在这里报道的 PAR 中，脂质运载蛋白基因家族成员的牛科特异性扩张，可能影响反刍动物的免疫调节和抗炎反应。对不同物种的 Y 染色体 X-d 区域的比较表明，五个已知是基因活性的全球调节因子和候选性别二态性基因的 X-Y 配子体是保守的。
