Mechanisms of chromosome motility during mammalian meiosis

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Mechanisms of chromosome motility during mammalian meiosis Project Summary/Abstract Meiosis is a specialized form of cell division of the germline that produces haploid gametes essential for sexual reproduction. A critical step in meiosis is the recombination between homologous chromosomes, also called meiotic crossover, required for the proper segregation of chromosomes into the daughter cells. Imperfect segregation prevents progression through meiosis and is a risk factor for infertility and miscarriage. A detailed understanding of meiotic crossover will enhance the knowledge of meiosis and hold implications for human reproductive biology. Essential to meiotic crossover is a remodeling process in the cell that involves connecting chromosomes in the nucleus to dynein in the cytosol via protein-protein interactions spanning the nuclear envelope. This event allows dynein to move all chromosomes along the nuclear envelope to facilitate the search and pairing of homologous chromosomes for undergoing crossover. A key player in this process is the SUN1-KASH5 LINC complex that spans the nuclear envelope to link chromosomes to dynein. Despite the importance of chromosome-nuclear envelope tethering and motility in mammalian meiosis, a molecular mechanism for this phenomenon is still lacking. Understanding how SUN1-KASH5 performs its meiosis- specific function will generate new knowledge to improve the diagnosis and treatment of fertility disorders. Using a multi-disciplinary approach that includes biochemical/biophysical methods, fixed and live-cell microscopy, single-molecule TIRF microscopy, membrane protein reconstitution, and a specialized mouse meiosis model system, this proposal aims to understand how dynein moves chromosomes to facilitate homolog pairing during meiosis. Aim 1 of the proposal will determine the structural basis, the dynamics, and the meiosis-specificity of the KASH5-dynein interaction instrumental to crossover. Interrogation in mouse spermatocytes will complement the in vitro studies to reveal how the KASH5-dynein interaction helps uphold mouse fertility. Aim 2 of this proposal will determine the higher-order structures adopted by SUN1-KASH5 at the nuclear envelope and how they enable cytosolic dynein forces to move entire chromosomes in the nucleus. This Aim and the grant proposal culminate in the dissection of the molecular mechanism underlying infertility in humans caused by a mutation in the gene encoding KASH5. The proposed studies will reveal how dynein and LINC complexes come together to facilitate the essential process of crossover during mammalian meiosis.