Nadarajan, S. | Search bioRxiv

bioRxiv2022

GRAS-1 is a conserved novel regulator of early meiotic chromosome dynamics in C. elegans

Chromosome movements and licensing of synapsis must be tightly regulated during early meiosis to ensure accurate chromosome segregation and avoid aneuploidy, although how these steps are coordinated is not fully understood. Here we show that GRAS-1, the worm homolog of mammalian GRASP/Tamalin and CYTIP, coordinates early meiotic events with cytoskeletal forces outside the nucleus. GRAS-1 localizes close to the nuclear envelope (NE) in early prophase I and interacts with NE and cytoskeleton proteins. Delayed homologous chromosome pairing, synaptonemal complex (SC) assembly, and DNA double-strand break repair progression are partially rescued by the expression of human CYTIP in gras-1 mutants, supporting functional conservation. However, Tamalin, Cytip double knockout mice do not exhibit obvious fertility or meiotic defects, suggesting evolutionary differences between mammals. gras-1 mutants show accelerated chromosome movement during early prophase I, implicating GRAS-1 in regulating chromosome dynamics. GRAS-1-mediated regulation of chromosome movement is DHC-1-dependent, placing it acting within the LINC-controlled pathway, and depends on GRAS-1 phosphorylation at a C-terminal S/T cluster. We propose that GRAS-1 serves as a scaffold for a multi-protein complex coordinating the early steps of homology search and licensing of SC assembly by regulating the pace of chromosome movement in early prophase I.

cell biology↗

bioRxiv2018

The tumor suppressor BRCA1/BARD1 complex localizes to the synaptonemal complex and regulates recombination under meiotic dysfunction in Caenorhabditis elegans

Breast cancer susceptibility gene 1(BRCA1) and binding partner BRCA1-associated RING domain protein 1 (BARD1) form an essential E3 ubiquitin ligase important for DNA damage repair and homologous recombination. In Caenorhabditis elegans BRCA1/BRC-1 and BARD1/BRD-1 orthologs are not essential, but function in DNA damage repair and homologous recombination, as well as in meiosis. In proliferating germ cells and in early meiotic prophase, BRC-1 and BRD-1 are nucleoplasmic, with enrichment at foci that partially overlap with the recombinase RAD-51. In mid-pachytene, BRC-1 and BRD-1 are observed on tracks, before concentrating to the short arms of bivalents, co-localizing with a central region component of the synaptonemal complex. We found that BRD-1 is essential for BRC-1 to associate with chromatin and the synaptonemal complex, but BRC-1 is not required for BRD-1 localization; the complex fails to properly localize in the absence of either meiotic recombination or chromosome synapsis. Inactivation of BRC-1/BRD-1 enhances the embryonic lethality of mutants that perturb chromosome synapsis and crossover recombination, suggesting that BRC-1/BRD-1 plays an important role in monitoring recombination in the context of the synaptonemal complex. We discovered that BRC-1/BRD-1 stabilizes the RAD51 filament when the formation of a crossover-intermediate is disrupted. Further, in the absence of BRC-1/BRD-1 crossover distribution is altered, and under meiotic dysfunction, crossover numbers are perturbed. Together, our studies indicate that BRC-1/BRD-1 localizes to the synaptonemal complex where it serves a checkpoint function to monitor and modulate meiotic recombination.\n\nProject SummaryOur genomes are passed down from one generation to the next through the specialized cell division program of meiosis. Meiosis is highly regulated to coordinate both the large scale chromosomal and fine scale DNA events to ensure fidelity. We analyzed the role of the tumor suppressor BRCA1/BARD1 complex in meiosis in the worm, Caenorhabditis elegans. We find that BRCA1/BARD1 localizes dynamically to the proteinaeous structure that aligns maternal and paternal chromosomes, where it regulates crossover recombination. Although BRCA1/BARD1 mutants have only subtle meiotic defects, we show that this complex plays a critical role in meiotic recombination when meiosis is perturbed. These results highlight the complexity of ensuring accurate transmission of the genome and uncover the requirement for this conserved complex in meiosis. As women carrying BRCA1 mutations with no indication of cancer have fertility defects, our results provide insight into why BRCA1 mutations impact reproductive success.

genetics↗