A previously described genetic screen performed in our lab identified multiple mutations that exhibit strong synthetic interactions with loss of
lin-35, the C. elegans Retinoblastoma protein ortholog. For example, LIN-35 and SLR-2, a C2H2 type Zn-Finger protein, co-regulate the expression of a large group of intestinal genes essential for nutrient utilization and intestinal function. However, single mutants of
lin-35 or
slr-2 exhibit no strong growth defects,
lin-35;
slr-2 double mutants uniformly arrest as starved L1 larva. A genome-wide RNAi screen for suppressors of
lin-35;
slr-2 larval arrest has identified 24 suppressors, most of which fall in to three functional classes: (1) ribosome biogenesis genes, (2) mitochondrial prohibitins, and (3) transcriptional regulators, most notably a class of chromatin remodeling genes shown to suppress the synthetic-multivulval (SynMuv) phenotype. In the case of prohibitins, recent work suggests a role in repressing fat store utilization. Consistent with this, Oil-Red-O fat staining of
lin-35;
slr-2 larva on
phb-1/2(RNAi) reveal a decrease in available fat stores compared to controls, consistent with a mechanism for suppression that mobilizes fat stores in order to bypass L1 starvation induced arrest. Interestingly, a number of the identified
lin-35;
slr-2 suppressors are capable of suppressing other unrelated
lin-35 synthetic phenotypes. Strikingly, RNAi of
hcf-1,
mes-4,
sin-3,
mrg-1, ZK1127.3, and
raga-1 suppress the majority of
lin-35 synthetic phenotypes tested. In fact,
hcf-1 strongly suppresses six of the seven
lin-35 synthetic phenotypes tested. Given that the majority of these promiscuous suppressors were characterized as SynMuv suppressors, we tested every member of this class on all available
lin-35 synthetic strains. We identified 9 additional genes that while incapable of suppressing
lin-35;
slr-2 arrest, suppress other
lin-35 synthetic phenotypes. Suppressors of multiple
lin-35 phenotypes likely have roles specific to LIN-35 functions, and could therefore be potential targets for anti-cancer therapies. For example, both
hcf-1 and
mes-4 suppress the hyper-proliferation defect in distal tip cells and intestinal nuclei observed of
lin-35;
fzr-1 mutants. Current work includes an additional genome-wide RNAi for suppressors of
lin-35;
ubc-18 pharyngeal defects. As expected, there is significant overlap with suppressors identified in the
lin-35;
slr-2 screen, however a large number of novel genes suggest mechanistic roles that are specific to pharyngeal development. To our knowlege, this work represents the first comprehensive screen in metazoan for suppressors of diverse synthetic phenotypes whose commonality lies in a common altered gene product.