Insulin/IGF-signaling (IIS) affects longevity, stress resistance and metabolism in worms, flies, and mammals. The Forkhead transcription factor DAF-16 is the major downstream effector of DAF-2/insulin receptor signaling, and is responsible for the activation and repression of genes that mediate the diverse effects of IIS. To identify DAF-16-regulated target genes, I used quantitative reverse-transcription PCR (qRT-PCR) to survey a set of 115 C. elegans genes containing a DAF-16 binding site at their promoter. One of the DAF-16 regulatory target genes identified is
hlh-13, the predicted ortholog of the mammalian transcription factor Ptf1a, a critical determinant of pancreatic development. A GFP reporter construct of
hlh-13 is expressed in all dopaminergic neurons, several unidentified ventral cord neurons during the L2/L3 developmental stages, and has DAF-16-responsive expression in the hypodermis. Since
hlh-13 represents a putative new DAF-16 transcriptional target, we tested whether loss of
hlh-13 may result in phenotypes commonly associated with insulin signaling, such as alterations in lifespan, stress resistance, and dauer formation. The lifespan of an
hlh-13 deletion mutant
hlh-13(
tm2279) is identical to controls in both a wild-type and IIS mutant background.
hlh-13(
tm2279) also does not exhibit differences in resistance to heat stress or oxidative stress (paraquat) compared to controls. However, we found that the
hlh-13(
tm2279) mutant worms recover faster from dauer arrest in a
daf-2(
e1370) mutant background at a sensitive temperature of 23C. The
hlh-13 mutant worms also recover faster from an extended L1 arrest, and are able to recover after a longer arrest than control worms. In addition, they are more resistant to an extended period of starvation than control worms in an IIS mutant background.
hlh-13 may regulate recovery from arrest and resistance to starvation by altering metabolism or fat storage. qRT-PCR of the
hlh-13 mutant worms shows lower levels of
acs-2, F25H5.3, and
fat-5, genes involved in mitochondrial beta-oxidation, glycolysis, and fatty acid desaturation, respectively. Also, staining with the lipophilic dye Nile Red shows altered fat storage in an
hlh-13(
tm2279);
daf-2(
e1370) double mutant. These results suggest intriguing roles for HLH-13 in dauer recovery and metabolism, and further studies are needed to fully understand the mechanisms involved in vivo.