Assembly and function of centromeric chromatin in Drosophila meiosis. Nicole L. Beier^1,2, Elaine M. Dunleavy^2,3, Walter Gorgescu⁴, Jonathan Tang⁴, Sylvain V. Costes⁴, Gary H. Karpen^1,2. 1) Department of Molecular and Cell Biology, University of California, Berkeley, CA; 2) Department of Genome Biology, Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA; 3) National University of Ireland, Galway, Ireland; 4) Department of Cancer and DNA Damage Responses, Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA.

   Centromeres are regions of eukaryotic chromosomes essential for faithful segregation of DNA, and are defined and maintained epigenetically throughout cellular generations in most eukaryotes by the histone H3 variant CENP-A. To maintain centromeric identity, new CENP-A must be assembled to replace the two-fold dilution that occurs after S phase and chromosome segregation. Aberrant incorporation of CENP-A causes ectopic kinetochore formation and aneuploidy. Recent studies have identified the timing and regulation of CENP-A incorporation in mitosis, predominantly in cultured cells. However, the function, regulation and cell cycle timing of CENP-A assembly in meiosis in tissues are currently unknown. We investigated the timing and requirements for assembly of the CENP-A homolog CID in male meiosis in Drosophila melanogaster. We found that CID is assembled during prophase of meiosis I and after exit from meiosis II. Prophase I loading is conserved in females. Surprisingly, these assembly phases are progressive, occurring over a period of hours to days. We also studied the requirements for CID assembly during meiosis, and found that the assembly factor CAL1 and the inner kinetochore protein CENP-C are both required. These studies demonstrate that the cell cycle timing of CID assembly in meiosis is different from previous observations in mitotic cells, including the length of time over which assembly occurs. Future investigations will focus on the function of CID assembly in meiotic prophase and the role of meiotic cell cycle factors in regulating assembly.