Accurate transmission of the genome from one generation to the next in sexually reproducing organisms depends on events that take place during meiosis, the cell division program that reduces the diploid genome by half. During meiosis oocytes and sperm also inherit complementary components of the centrosome, which is part of the chromosome segregation machinery in the early embryonic divisions. Sperm provide a pair of attached centrioles and oocytes provide the pericentriolar material at fertilization, together forming the first centrosome of the embryo. Accurate inheritance of chromosomes and centrosome components in meiosis is critical to avoid aneuploidy in the embryo. We found new roles for the conserved meiosis HORMA proteins. In the first meiotic division, the HTP-1 and HTP-2 HORMA proteins prevent premature removal of the meiosis cohesin component REC-8 from chromosomes. HTP-1/2 antagonize the Separase protease SEP-1 that has been proposed to remove REC-8 from chromosomes. We also found that the HORMA protein HIM-3, HTP-1/2 prevent separation of the centrioles during the second meiotic division in spermatocytes. Centriole pairs remain together at the end of the second spermatocyte division. This prevents an extra duplication of the centrioles, which can result in the one-cell embryo making four centrosomes. REC- 8 is required to prevent abnormal centriole separation, whereas SEP-1 can promote centriole pair separation. We propose to adapt emerging optogenetic techniques to expand our understanding of the basic mechanisms by which the HORMA/SEP-1/REC-8 protein module regulates sister chromatid and centriole inheritance in meiosis. Using optogenetic degron and split-fluorophore analyses, we will determine the genetic and protein-protein interaction critical for preventing separation chromosomes and/or centrioles. We will also adapt an in vivo fluorescent sensor for SEP-1 cleavage of REC-8 in chromosomes and centrosomes, to test SEP-1 cleavage of REC-8 in wild type and in horma mutant germlines, and in germlines of other mutants expected to regulate chromosome or centriole separation. In addition, we will perform both biochemical and genetic screens to identify more proteins involved in maintaining together the centriole pair in the second meiotic division in spermatocytes. Together these approaches will uncover whether HORMA, SEP-1, and REC-8 proteins function in an analogous fashion to keep chromatids and centrioles together in meiosis.
These aims will provide insight into mechanisms that postpone centriole separation in spermatocyte and sperm in most multicellular organisms. In addition to uncovering molecular mechanisms that prevent aneuploidy in meiosis and the one cell embryo, completion of our aims will broaden our knowledge of basic mechanisms of genome maintenance. Achieving these goals will allow us to expand and develop the only in vivo system where the Separase/cohesin module regulates centriole separation and will generate a tool-kit for studying proteins with multiple roles in meiosis.
Aneuploidy is a common cause of miscarriages, genetic disorders and birth defects, and is a driver of oncogenesis. The proposed research investigates the mechanism by which meiotic HORMA proteins prevent errors in chromosome and centrosome inheritance in meiosis and the early embryo. Completion of our aims will impact the field of reproductive biology, will further our understanding on the etiology of congenital birth defects due to aneuploidy, and will also broaden our understanding of basic mechanisms of genome maintenance.
