Briscoe A, Tomkiel J E
Center for Molecular Medicine and Genetics, Wayne State University, Detroit, Michigan 48202, USA.
Genetics. 2000 Jul;155(3):1195-211. doi: 10.1093/genetics/155.3.1195.
In Drosophila melanogaster, the rDNA loci function in ribosome biogenesis and nucleolar formation and also as sex chromosome pairing sites in male meiosis. These activities are not dependent on the heterochromatic location of the rDNA, because euchromatic transgenes are competent to form nucleoli and restore pairing to rDNA-deficient X chromosomes. These transgene studies, however, do not address requirements for the function of the endogenous rDNA loci within the heterochromatin. Here we describe two chromosome rearrangements that disrupt rDNA functions. Both rearrangements are translocations that cause an extreme bobbed visible phenotype and XY nondisjunction and meiotic drive in males. However, neither rearrangement interacts with a specific Y chromosome, Ymal(+), that induces male sterility in combination with rDNA deletions. Molecular studies show that the translocations are not associated with gross rearrangements of the rDNA repeat arrays. Rather, suppression of the bobbed phenotypes by Y heterochromatin suggests that decreased rDNA function is caused by a chromosomal position effect. While both translocations affect rDNA transcription, only one disrupts meiotic XY pairing, indicating that there are different cis-acting requirements for rDNA transcription and rDNA-mediated meiotic pairing.
在黑腹果蝇中，核糖体DNA（rDNA）位点在核糖体生物合成和核仁形成中发挥作用，同时在雄性减数分裂中作为性染色体配对位点。这些活动并不依赖于rDNA的异染色质定位，因为常染色质转基因能够形成核仁并恢复与rDNA缺陷型X染色体的配对。然而，这些转基因研究并未涉及异染色质内内源rDNA位点功能的要求。在这里，我们描述了两种破坏rDNA功能的染色体重排。这两种重排都是易位，会导致极端的截毛可见表型以及雄性中的XY不分离和减数分裂驱动。然而，这两种重排都不与特定的Y染色体Ymal(+)相互作用，Ymal(+)与rDNA缺失结合会导致雄性不育。分子研究表明，这些易位与rDNA重复阵列的大规模重排无关。相反，Y异染色质对截毛表型的抑制表明，rDNA功能的降低是由染色体位置效应引起的。虽然这两种易位都影响rDNA转录，但只有一种破坏减数分裂XY配对，这表明rDNA转录和rDNA介导的减数分裂配对存在不同的顺式作用要求。
