# Transcriptome- and phenotype-based epistasis analysis in Caenorhabditis elegans reveals daf-16/FoxO-dependent and independent effects of daf-2/InsR in L1 starvation and recovery

## TL;DR

This study in C. elegans shows that reduced insulin signaling during starvation affects survival through DAF-16/FoxO but preserves reproduction via an unknown mechanism.

## Contribution

Identification of 4,653 putative DAF-16/FoxO targets and evidence for DAF-16-dependent and -independent effects of insulin signaling during starvation.

## Key findings

- Disruption of daf-2/InsR during starvation causes daf-16-dependent changes in gene expression and survival.
- DAF-16 is not required for reproduction after starvation, and daf-2 loss preserves reproduction independently of DAF-16.
- Reduced insulin signaling during L1 starvation is largely DAF-16-dependent but involves additional effectors for reproduction.

## Abstract

Reduced insulin/IGF signaling (IIS) in Caenorhabditis elegans increases starvation resistance in a daf-16/FoxO-dependent fashion, but it is unclear whether the effects of reduced IIS are entirely dependent on daf-16/FoxO. We used RNA sequencing and phenotypic analysis of L1 starvation resistance to assess epistasis between daf-2/InsR and daf-16/FoxO. We identified 4,653 putative DAF-16/FoxO targets, many of which had not been previously identified, providing a valuable reference data set. Differential gene expression and increased survival caused by disruption of daf-2/InsR during starvation are daf-16-dependent. The effect of daf-2/InsR on growth following starvation is largely but not entirely daf-16-dependent. Notably, daf-16 is dispensable for reproduction following extended starvation, and daf-2 loss preserves reproductive success independent of daf-16. These results show that the effects of reduced IIS during L1 starvation are daf-16/FoxO-dependent but that IIS engages 1 or more additional effectors to buffer larval growth and especially reproduction from persistent effects of early life starvation.

Nutrient availability affects animal development and physiology by altering insulin signaling. The roundworm Caenorhabditis elegans has proven to be a valuable model to study the effects of altered insulin signaling. Fisher et al. provide a valuable gene expression dataset from C. elegans to investigate the role of insulin signaling during starvation. The authors also show that reduced insulin signaling during starvation acts exclusively through the conserved transcription factor DAF-16/FoxO to affect gene expression and survival. In contrast, they show that reduced insulin signaling does not act through DAF-16 to preserve reproductive potential following starvation, indicating the requirement of an unknown effector.