The decision to proceed to dauer stage requires the integration of multiple sensory inputs such as food, pheromone and temperature. The sum of these inputs triggers the execution of a remodelling program which affects the anatomy and physiology of the animal. Molecular genetic analysis has identified a TGF-beta like (DAF-7) pathway and an insulin-like (DAF-2) pathway which are thought to couple sensory signals to the subsequent animal remodelling through transcriptional regulation of target genes. Notably, downregulation of DAF-7 and DAF-2 leads to activation of DAF-3 Smad protein and DAF-16 Forkhead transcription factor, respectively. In contrast to the detailed knowledge of the DAF-2 and DAF-7 signalling cascades, only a handful of DAF-3 and DAF-16 target genes are currently known. Using a candidate gene approach, we focused on the function and transcriptional regulation of
daf-9 which is genetically downstream of
daf-3 and
daf-16. We generated a
daf-9::gfp fusion gene which rescues the strong loss of function
daf-9 (
e1406) mutation. Consistent with Gerisch et al, 2001 and Jia et al, 2002, we detected
daf-9::gfp expression in a pair of inner labial (IL1) neurons in L1 larvae which persists in all larval stages and in adults, in the hypodermis from mid-L2 stage and in the spermatheca of adult animals. No dramatic change was observed in
daf-9::gfp expression in animals where DAF-2 or DAF-7 signalling pathway was attenuated. In contrast, hypodermal
daf-9::gfp is eliminated in
daf-12(lf) mutant animals. Hence, DAF-12 appears to activate
daf-9 gene expression in the hypodermis and this suggests an auto-inhibition mechanism by which DAF-12 modulates its own activity by upregulating
daf-9. We investigated the site of action of DAF-9 by generating transgenes which direct
daf-9 expression in a tissue-specific manner.
daf-9 (
e1406) mutant animals can be fully rescued and reach adulthood by pan-neuronal expression of
daf-9 using the
unc-14 promoter or hypodermal expression of
daf-9 using the
dpy-7 promoter. This indicates that either neuronal or hypodermal
daf-9 expression is sufficient for reproductive development and that DAF-9 is likely to act in a cell non-autonomous manner. Furthermore,
unc-14promoter::
daf-9::gfp or
dpy-7promoter::
daf-9::gfp is able to suppress dauer arrest of
daf-7 (
e1372) mutant animals, reinforcing the notion that the hormonal signalling pathway of DAF-9 acts either downstream or in parallel to the DAF-7 pathway.