The C. elegans germline is an excellent model for studying cellular responses to DNA damage. In particular this is due to the spatial separation, in the germline, of the two DNA damage checkpoint responses: cell cycle arrest and apoptosis. We have identified a gene,
lin-61, which is essential for both of these processes. Mitotic cell cycle arrest and meiotic apoptosis is defective in
lin-61 mutants following damage. In addition, these mutants are hypersensitive to ionizing radiation, indicating a role in protection from DNA damage. Homologues of
lin-61 are implicated as tumor suppressors in other animals. Mutants of the Drosophila homologue, l(3)mbt, develop optic neuroblast tumors while the human homologue is frequently deleted in certain human malignancies. These proteins are members of a class of conserved transcriptional repressors. Their defining feature is the presence of so-called malignant brain tumor (MBT) domains, which have recently been shown to compact chromatin by directly interacting with methylated histones. Previously, Harrison et al (Genetics 2007) showed
lin-61 to be a class B synMuv gene, which acts to control vulval development. Here we reveal a novel role for
lin-61 in protecting the germline from DNA damage. At this meeting, we are particularly focusing on the apoptotic role of
lin-61. Following damage, the pro-apoptotic proteins,
egl-1 and
ced-13 are up-regulated in a manner dependent on the
p53 homologue,
cep-1. Using qRT-PCR, we show that up-regulation of
egl-1 and
ced-13 is normal in
lin-61 mutants, indicating that
lin-61 acts in parallel to, or downstream of,
cep-1. Further, the expression level of the anti-apoptotic gene
ced-9/Bcl2 is also normal in
lin-61 mutants. We are now using genetic analysis to determine how
lin-61 mutants are defective for damage-induced apoptosis. The Drosophila homologue of LIN-61 is part of a transcriptional repressor complex. To search for components of a putative LIN-61 complex and to find factors that act redundantly with
lin-61, we performed a genome-wide RNAi screen for genes that are essential for viability in
lin-61 mutants but are dispensable in wild type worms. Intriguingly, this screen identified, in addition to several other synMuv genes, two components of the nuclear transcription factor Y (NF-Y). In mammalian cells, this conserved transcription factor works with
p53 to modulate the expression of cell cycle genes and apoptotic genes such as the
ced-9 homologue, Bcl2. We are investigating the genetic connection between
lin-61 and NF-Y and their respective contributions to the DNA damage response.