In the platypus a meiotic chain of ten sex chromosomes shares genes with the bird Z and mammal X chromosomes
In the platypus a meiotic chain of ten sex chromosomes shares genes with the bird Z and mammal X chromosomes
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DOI：
10.1038/nature03021
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发表时间：
2004-12-16
期刊：
影响因子：
64.8
通讯作者：
Graves, JAM
中科院分区：
文献类型：
--
作者：
Grützner, F;Rens, W;Graves, JAM
鸭嘴兽被发现两个世纪后，单孔类动物的染色体系统仍然令人深感困惑。据称，男性 (1) 或两性 (2-4) 的核型含有数条不配对的染色体（包括 X 染色体），这些染色体在减数分裂时形成多染色体链。这种减数分裂链存在于植物(5)和昆虫(6)中，但在脊椎动物(7)中很少见。几十年来，鸭嘴兽染色体系统如何确定性别和产生平衡配子一直存在争议(1-4)。在这里，我们证明鸭嘴兽有 5 条雄性特有的染色体（Y 染色体），并且 5 条染色体在雄性中存在一个拷贝，在雌性中存在两个拷贝（X 染色体）。这十条染色体在雄性减数分裂时形成一条多价链，采用交替模式分离成带有 XXXXX 的精子和带有 YYYYY 的精子。这些性染色体中的哪一条（如果有的话）携带一个或多个性别决定基因仍然未知。与人类 X 染色体同源的最大 X 染色体位于链的一端，与鸟类 Z 染色体同源的染色体位于另一端附近。这表明哺乳动物和鸟类性染色体系统之间存在进化联系，此前人们认为它们是独立进化的。
Two centuries after the duck-billed platypus was discovered, monotreme chromosome systems remain deeply puzzling. Karyotypes of males(1), or of both sexes(2-4), were claimed to contain several unpaired chromosomes ( including the X chromosome) that form a multi-chromosomal chain at meiosis. Such meiotic chains exist in plants(5) and insects(6) but are rare in vertebrates(7). How the platypus chromosome system works to determine sex and produce balanced gametes has been controversial for decades(1-4). Here we demonstrate that platypus have five male-specific chromosomes (Y chromosomes) and five chromosomes present in one copy in males and two copies in females ( X chromosomes). These ten chromosomes form a multivalent chain at male meiosis, adopting an alternating pattern to segregate into XXXXX-bearing and YYYYY-bearing sperm. Which, if any, of these sex chromosomes bears one or more sex-determining genes remains unknown. The largest X chromosome, with homology to the human X chromosome, lies at one end of the chain, and a chromosome with homology to the bird Z chromosome lies near the other end. This suggests an evolutionary link between mammal and bird sex chromosome systems, which were previously thought to have evolved independently.