Regulation of chromosome segregation by ORD and dRING during Drosophila meiosis.

摘要

Accurate segregation of meiotic chromosomes requires that sister-chromatids remain physically associated from the time of their synthesis during S phase until they segregate toward opposite poles at anaphase II. In Drosophila melanogaster meiosis, physical association of sister chromatids, known as sister-chromatid cohesion, requires the protein product of the orientation disruptor (ord) gene. Genetic and cytological analyses of ord mutants indicate that sister chromatids separate precociously in the absence of ORD activity, resulting in random chromosome segregation during both meiotic divisions.; To understand the molecular basis of ORD activity more fully, we localized ORD protein in Drosophila spermatocytes using immunofluorescence and demonstrate that ORD associates with centromeres of meiotic chromosomes from early G2 through anaphase II. Maintenance of ORD at centromeres until anaphase II requires functional MEI-S332 protein, as centromeric ORD signal disappears during anaphase I in mei-S3321 mutant spermatocytes. Using fluorescence in situ hybridization (FISH), we show that defects in centromeric cohesion manifest during late G2 in spermatocytes that lack ORD activity and are extensive after prophase I chromosome condensation. Our data indicate that association of ORD protein with centromeres promotes normal centromeric cohesion from late interphase through anaphase II of meiosis.; We also provide experimental evidence that a functional interaction exists in Drosophila meiotic cells between ORD and dRING, a Polycomb group protein that physically interacts with ORD in a yeast two-hybrid assay. We show that a missense mutation in ord that causes severe defects in meiotic sister-chromatid cohesion completely abolishes the yeast two-hybrid interaction with dRING. Moreover, this mutant ORD protein exhibits dramatic localization defects in primary spermatocytes. During mid-late G2 of meiosis, we observe that ORD localizes to the chromosome arms where it extensively colocalizes with dRING. Furthermore, germline expression of a truncated dRING molecule that contains the ORD-interaction domain enhances levels of chromosome missegregation in ord mutant males and females. These results are consistent with the model that interaction of ORD and dRING facilitates proper segregation of chromosomes during Drosophila meiosis.