The BRCA1-BARD1 complex associates with the synaptonemal complex and pro-crossover factors and influences RAD-51 dynamics during Caenorhabditis elegans meiosis

Abstract

During meiosis, the maternal and paternal homologous chromosomes must align along their entire length and recombine to achieve faithful segregation in the gametes. Meiotic recombination is accomplished through the formation of DNA double-strand breaks, a subset of which can mature into crossovers to link the parental homologous chromosomes and promote their segregation. Breast and ovarian cancer susceptibility protein BRCA1 and its heterodimeric partner BARD1 play a pivotal role in DNA repair in mitotic cells; however, their functions in gametogenesis are less well understood. Here we show that localization of BRC-1 and BRD-1 (Caenorhabditis elegans orthologues of BRCA1 and BARD1) is dynamic during meiotic prophase I; they ultimately becoming concentrated at regions surrounding the presumptive crossover sites, co-localizing with the pro-crossover factors COSA-1, MSH-5 and ZHP-3. The synaptonemal complex is essential for BRC-1 loading onto chromosomes but recombination is not. BRC-1 forms an in vivo complex with the synaptonemal complex component SYP-3 and the crossover-promoting factor MSH-5. Furthermore, BRC-1 is essential for efficient stage-specific recruitment of the RAD-51 recombinase to DNA damage sites when synapsis is impaired and upon induction of exogenous DNA double-strand breaks. Taken together, our data provide new insights into the localization and meiotic function of the BRC-1-BRD-1 complex and highlight their essential role in DNA double-strand break repair during gametogenesis.\n\nAuthor summarySexually reproducing species rely on meiosis to transmit their genetic information across generations. Parental chromosomes (homologues) undergo many distinctive processes in their complex journey from attachment to segregation. The physiological induction of DNA double strand breaks is crucial for promoting correct chromosome segregation: they are needed to activate the DNA repair machinery responsible for creating physical connections, or crossovers (COs), between the homologues. In turn, crossovers promote the accurate segregation of the chromosomes in daughter cells. The BRCA1-BARD1 complex has a pivotal role during DNA repair in somatic cells and is exclusively located on unaligned chromosomal regions during mammalian meiosis. We show that in Caenorhabditis elegans, BRCA1 and BARD1 localize to chromosomes at all stages of meiotic prophase I and are enriched at presumptive crossover sites. We found that BRCA1 promotes DNA loading of the repair factor RAD-51 in specific mutant backgrounds and upon exogenous damage induction. Our data provide evidence for a direct physical association between BRCA1 and pro-crossover factors (including the synaptonemal complex) and identify an important role for BRCA1 in stimulating meiotic DNA repair. Further studies are necessary to identify the substrates acted upon by BRCA1-BARD1 complex to maintain genome stability in the gametes.