Essential role of brc-2 in chromosome integrity of germ cells in C. elegans

brc-2, an ortholog of BRCA2 in Caenorhabditis elegans, is essential in the maintenance of genetic integrity. In C. elegans, cellular location correlates with meiotic progression, and transgene-induced cosuppression is observed in the germ line but not in somatic cells. We used these unique features to dissect the role of brc-2 in the germ line from that in somatic cells. In situ hybridization of wild type animals revealed that brc-2 gene expression was higher in oocytes than in other germline cells, and was barely detectable in mitotic cells. In contrast, germ cells containing multicopies of the brc-2 transgene showed no significant in situ hybridization signal at any oogenesis stage, confirming that brc-2 expression was functionally cosuppressed in the transgenic germ line. RAD-51 foci formation in response to DNA damage was abrogated in brc-2-cosuppressed germ cells, whereas wild-type germ cells showed strong RAD-51 foci formation. These germ cells exhibited massive chromosome fragmentation and decompaction instead of six bivalent chromosomes in diakinesis. Accordingly, lethality was observed after the early stage of germline development. These results suggest that brc-2 plays essential roles in chromosome integrity in early prophase, and therefore is crucial in meiotic progression and embryonic survival.