A proposed role for the Polycomb group protein dRING in meiotic sister-chromatid cohesion
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ORD protein is required for accurate chromosome segregation during male and female meiosis in Drosophila melanogaster. Null ord mutations result in random segregation of sister chromatids during both meiotic divisions because cohesion is completely abolished prior to kinetochore capture of microtubules during meiosis I. Previous analyses of mutant ord alleles have led us to propose that the C-terminal half of the ORD protein mediates protein-protein interactions that are essential for sister-chromatid cohesion. To identify proteins that interact with ORD, we conducted a yeast two-hybrid screen using an ORD bait and isolated dRING, a core subunit of the Drosophila Polycomb repressive complex 1. We show that a missense mutation in ORD completely ablates the two-hybrid interaction with dRING and prevents nuclear retention of the mutant ORD protein in male meiotic cells. Using affinity-purified antibodies generated against full-length recombinant dRING, we demonstrate that dRING protein is expressed in the male and female gonads and colocalizes extensively with ORD on the chromatin of primary spermatocytes during G2 of meiosis. Our results suggest a novel role for the Polycomb group protein dRING and are consistent with the model that interaction of dRING and ORD is required to promote the proper segregation of meiotic chromosomes.
KeywordsChromosome Condensation Meiotic Chromosome Primary Spermatocyte Cohesin Subunit Centromeric Cohesion
We thank H. Saumweber for providing T40 nuclear lamin monoclonal antibodies. We acknowledge members of the Bickel laboratory for helpful discussions and critical reading of the manuscript. We thank Colleen Raymond, Jennifer Thibert and Patrice Salome for help with the two-hybrid screen and directed two-hybrid assay. Funding for the two-hybrid screen was provided by March of Dimes to T.O.W. E.M.B was supported in part by National Institutes of Health Training Grant (GM-08704). S.E.B was funded by March of Dimes (5-FY98-738) and National Institutes of Health (GM-59354).
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