Transcriptional regulation by the insulin signaling effectors DAF-16/FoxO and SKN-1/Nrf in C. elegans

Abstract

Over the past two decades, there has been significant growth in our understanding of the genetics underlying aging, catalyzed by the discovery that a single-gene mutation can dramatically extend lifespan in the roundworm <italic>Caenorhabditis elegans</italic>. The first such mutation, which results in a doubling of the animal's lifespan, was found to occur in <italic>daf-2</italic>, the worm's insulin receptor; the lifespan extension was found to be completely dependent on <italic>daf-16</italic>, the worm's FOXO transcription factor. The transcriptional targets of DAF-16 have previously been studied using a variety of whole-genome approaches; these studies have revealed a diverse array of targets, some of which have been shown to influence aging.

As <italic>C. elegans</italic> is a multi-tissue organism, and DAF-2 and DAF-16 activity in particular tissues influence longevity, it is important to explore where DAF-16 may be acting to regulate its targets, and where the targets themselves are expressed. In Chapter 2, we identify the transcriptional targets of DAF-16 that is expressed in specific tissues. We find that DAF-16 activity in specific tissues regulates distinct target sets, and we reveal surprisingly complex patterns of regulation by DAF-16 in different tissues. In Chapter 3, we introduce a novel method to isolate individual cell and tissue types from adult <italic>C. elegans</italic> and profile their transcriptomes. We apply the method to identify the targets of endogenous DAF-16 within the neurons, hypodermis, and muscle.

In Chapter 4, we further study the complex network modulated by insulin/IGF-1 signaling by identifying the transcriptional targets of SKN-1, which is regulated in a parallel manner as DAF-16 by DAF-2. Our results advance our understanding of the complex direct and indirect actions of DAF-16 and SKN-1 in mediating the transcriptional outputs of insulin signaling.