The Forkhead box A (FoxA) family of transcription factors play key roles in digestive tract development in many animals. In C. elegans,
pha-4 encodes the sole FoxA transcription factor, which is required for pharynx development (Mango et al., 1994; Horner et al., 1998; Kalb et al., 1998). The timing, location, and level of PHA-4 expression are vital for its function; however, little is known about how
pha-4 or other FoxA proteins are regulated. To discover genes that interact with PHA-4, we conducted an RNAi screen for suppressors of lethality caused by the loss of
pha-4. Because complete inactivation of
pha-4 results in loss of pharynx and larval arrest, we used a conditional strain,
smg-1(ts);
pha-4(
zu225), which relies on a temperature-sensitive allele of the nonsense mediated decay (NMD) component
smg-1 and a nonsense mutation in
pha-4 (Kaltenbach et al., 2005; Gaudet et al., 2002). At 24C, the NMD pathway is inactive and
pha-4 is expressed and worms live, but at 20C, the NMD pathway is active, which causes degradation of
pha-4 transcripts and larval arrest. We call this configuration
pha-4(ts). Our initial screen used an RNAi library of almost 17,000 clones (Kamath et al., 2003) and identified close to 1000 potential suppressors. We expected two classes of suppressors: informational suppressors and suppressors that were more specific to the
pha-4 pathway. We identfied three of the four known NMD pathway components represented in the RNAi library, as well as other genes that likely play a role in RNA metabolism. We also discovered four previously discovered
pha-4 suppressors, indicating that our screen could successfully find
pha-4(ts) suppressors. The remaining candidate genes are being retested to determine if they are true suppressors. The list of candidates includes genes involved in signaling and in transcription. Our future goals will be to determine the nature of the interactions of these factors with
pha-4 and the roles these genes play in promoting pharynx development.