Identification and Characterization of a gene required for meiosis I mono-orientation of sister chromatids in Drosophila

Prior to meiosis, kinetochores of sister chromatids are replicated, functional and important for orienting chromosome alignment at the metaphase plate. At meiosis I sister kinetochores must attach to the same spindle pole to ensure that sister chromatids are segregated to the same daughter cell. In yeasts, the monopolin complex mediates this co-orientation of sister kinetochores to promote proper chromosome segregation. Monopolin constituents are not well conserved across phyla; Meikin appears to carry out the same function in humans and other organisms. Analogues to monopolin components have not yet been identified in the fruit fly Drosophila melanogaster; despite a conserved function of chromosome segregation in meiosis I. Here, I describe an EMS-induced meiotic mutant, CG30383Z, in Drosophila melanogaster that is defective in co-orientation of sister kinetochores at meiosis I. In genetic tests of chromosome transmission, mutants in CG30383Z produce both reductional nondisjunction of homologs and equational nondisjunction of sister chromatids. Complementation tests using a deletion allele have revealed that this is the null phenotype. Furthermore, using fluorescence in situ hybridization, I observed that mutant CG30383Z sister chromatids had separated and segregated to opposite poles at meiosis I in 69.3% of meiotic cells. All aspects of this phenotype suggest that I have identified the first component of the monopolin complex in flies