MicroRNAs (miRNAs) are small (~22nt) noncoding RNA transcripts that repress the translation of specific mRNA targets by binding to complementary sequences in their 3 UTRs. Two homologous RNA binding proteins, ALG-1 and ALG-2, are redundantly required in C. elegans for the processing and possibly also the function
lin-4 and
let-7 miRNAs. Experimental depletion of
alg-1/alg-2 causes highly pleiotropic phenotypes, including embryonic lethality and slow larval growth, which are far more severe that those associated with the absence of
lin-4 and
let-7. The combined activities of
alg-1/alg-2 are therefore implicated in several other essential developmental processes. One hypothesis is that alg- 1/alg-2 are required for the processing and function of many of the ~100 miRNAs found in C. elegans and are therefore required for the proper regulation of diverse developmental programs that require miRNAs. According to this model, the suite of phenotypes associated with the depletion of
alg-1/alg-2 would result from the misregulation of several mRNA targets required in diverse developmental/regulatory pathways. Consistent with this prediction, the depletion of
alg-1/alg-2 affects the processing of several miRNAs in addition to
lin-4 and
let-7. To test the implications of this hypothesis and to further characterize microRNA processing in vivo, we have developed a genetic strategy to identify other cellular factors that contribute to miRNA processing/function while also detecting new developmental pathways that require
alg-1/alg-2 activities. We simultaneously deplete two genes by exposing worms to two bacterial sources of food, each expressing an individual dsRNA specific to a different targeted transcript. We have identified C. elegans RNAi library clones that when co-depleted with
alg-1/alg-2, result in an enhancement or suppression of
alg-1/alg-2 embryonic lethal phenotypes. To date, 2428 clones from chromosome I (~90% of the ORFs on this chromosome and ~13% of predicted C. elegans ORFs) have been screened for those that enhance the embryonic lethality associated with
alg-1/alg-2 depletion. Less that 1% of the RNAi clones tested exhibited a synthetic lethal phenotype when co-depleted with
alg-1/alg-2. One major class of enhancer clones encode RNA-binding proteins and translational machinery, consistent with the presumption that miRNAs function in translational regulation. A second class of
alg-1/alg-2 enhancers is composed of clones encoding putative transcriptional factors. A full description and further characterization of these genetic interactions will be presented.