Supplemental Material for Germoglio and Adamo, 2018

The
evolutionary conserved RAD-51 protein is essential for homologous recombination
in the germ line as well as homologous repair of DNA double strand breaks in
all eukaryotic cells. In the nematode Caenorhabditis
elegans the rad-51 gene is
transcribed into messenger-RNAs potentially coding three alternative protein
isoforms. Null rad-51 alleles display
embryonic lethality, severe defects in chromosome structure and high level of
germ line apoptosis. To dissect its functions, we genetically modified the C. elegans rad-51 gene by CRISPR/Cas9
genome-editing technology, obtaining a separation-of-function (sfi-) mutant
allele that only disrupts the long transcript isoform. This mutant shows no
defects in an otherwise wild-type meiosis and is able to activate physiological
germ cell death, which occurs at the late pachytene stage. However, although
the mutant is competent in DNA damage checkpoint activation after exposure to
ionizing radiation, it is defective for induction of DNA-damage induced
apoptosis in meiotic germ cells. These results suggest that RAD-51 plays a
novel role in germline apoptosis independent of RAD-51-mediated strand invasion
for homologous recombination.