Park H S, Yamamoto M T
Department of Applied Biology, Kyoto Institute of Technology, Matsugasaki, Sakyo, Kyoto 606, Japan
Chromosoma. 1995 Jul;103(10):700-7. doi: 10.1007/BF00344231.
In Drosophila melanogaster males, sex chromosome pairing at meiosis is ensured by so-called pairing site(s) located discretely in the centric heterochromatin. The property of the pairing sites is not well understood. Recently, an hypothesis has been proposed that 240 bp repeats in the nontranscribed spacer region of rDNA function as the pairing sites in male meiosis. However, considerable cytogenetic evidence exists that is contrary to this hypothesis. Hence, the question is whether the chromosomal rDNA clusters, in which a high copy number of 240 bp repeats exists, are involved in the pairing. In order to resolve the problem we X-rayed Drosophila carrying the X chromosome inversion In(1)scV2L sc8R and generated free, mini-X chromosomes carrying a substantial amount of rDNA. We defined cytogenetically the size of the mini-chromosomes and studied their meiotic behavior. Our results demonstrate that the heterochromatin at the distal end of the inversion, whose length is approximately 0.4 times that of the fourth chromosome, includes a meiotic pairing site in the male. We discuss the cytological location of the pairing site and the possible role of rDNA in meiotic pairing.
在黑腹果蝇雄性个体中，减数分裂时性染色体配对是由位于着丝粒异染色质中离散分布的所谓配对位点来确保的。配对位点的特性尚未得到很好的理解。最近，有人提出核糖体DNA（rDNA）非转录间隔区中的240 bp重复序列在雄性减数分裂中作为配对位点。然而，存在大量与该假说相悖的细胞遗传学证据。因此，问题在于存在高拷贝数240 bp重复序列的染色体rDNA簇是否参与配对。为了解决这个问题，我们用X射线照射携带X染色体倒位In(1)scV2L sc8R的果蝇，并产生了携带大量rDNA的游离小X染色体。我们通过细胞遗传学方法确定了小染色体的大小，并研究了它们的减数分裂行为。我们的结果表明，倒位远端的异染色质，其长度约为第四条染色体的0.4倍，在雄性中包含一个减数分裂配对位点。我们讨论了配对位点的细胞学位置以及rDNA在减数分裂配对中的可能作用。
