In mice, mutation of brca1 results in embryonic lethality, which is partially suppressed by 53bp1 mutation. In contrast, mutation of the C. elegans BRCA1 ortholog, brc-1 , or its binding partner, brd-1 , lead to only mild embryonic lethality. We show that in C. elegans , brc-1 and brd-1 embryonic lethality is enhanced when 53bp1 ortholog, hsr-9 , is also mutated. This is not a consequence of activating polq-1 -dependent microhomology-mediated end joining, as polq-1 mutation does not suppress embryonic lethality of hsr-9 ; brc-1 mutants. Together, these results suggest that BRC-1 - BRD-1 and HSR-9 function in parallel pathways and do not act antagonistically as in mammals.
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