Y 连锁基因在黑腹果蝇中的点状染色体易位。
Translocation of Y-linked genes to the dot chromosome in Drosophila pseudoobscura.
机构信息
Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, USA.
出版信息
Mol Biol Evol. 2010 Jul;27(7):1612-20. doi: 10.1093/molbev/msq045. Epub 2010 Feb 10.
One of the most striking cases of sex chromosome reorganization in Drosophila occurred in the lineage ancestral to Drosophila pseudoobscura, where there was a translocation of Y-linked genes to an autosome. These genes went from being present only in males, never recombining, and having an effective population size of 0.5N to a state of autosomal linkage, where they are passed through both sexes, may recombine, and their effective population size has quadrupled. These genes appear to be functional, and they underwent a drastic reduction in intron size after the translocation. A Y-autosome translocation may pose problems in meiosis if the rDNA locus responsible for X-Y pairing had also moved to an autosome. In this study, we demonstrate that the Y-autosome translocation moved Y-linked genes onto the dot chromosome, a small, mainly heterochromatic autosome with some sex chromosome-like properties. The rDNA repeats occur exclusively on the X chromosome in D. pseudoobscura, but we found that the new Y chromosome of this species harbors four clusters bearing only the intergenic spacer region (IGS) of the rDNA repeats. This arrangement appears analogous to the situation in Drosophila simulans, where X-rDNA to Y-IGS pairing could be responsible for X-Y chromosome pairing. We postulate that the nascent D. pseudoobscura Y chromosome acquired and amplified copies of the IGS, suggesting a potential mechanism for X-Y pairing in D. pseudoobscura.
果蝇中最引人注目的性染色体重组案例之一发生在果蝇拟暗果蝇的祖先谱系中,其中存在着将 Y 连锁基因易位到一条常染色体上的现象。这些基因从只存在于雄性、从不重组且有效种群大小为 0.5N 的状态,变成了常染色体连锁的状态,它们通过两性传递,可能发生重组,其有效种群大小增加了四倍。这些基因似乎是有功能的,并且在易位后经历了内含子大小的急剧减少。如果负责 X-Y 配对的 rDNA 基因座也转移到了常染色体上,那么 Y-常染色体易位可能会在减数分裂中带来问题。在这项研究中,我们证明 Y-常染色体易位将 Y 连锁基因转移到了点状染色体上,点状染色体是一条小型的、主要为异染色质的常染色体,具有一些类似于性染色体的特性。rDNA 重复序列在果蝇拟暗果蝇中仅存在于 X 染色体上,但我们发现该物种的新 Y 染色体上有四个簇,仅携带 rDNA 重复的基因间区(IGS)。这种排列方式类似于果蝇 simulans 中的情况,其中 X-rDNA 到 Y-IGS 的配对可能负责 X-Y 染色体的配对。我们假设新形成的果蝇拟暗 Y 染色体获得并扩增了 IGS 的拷贝,这表明了果蝇拟暗 X-Y 配对的一种潜在机制。