Heat shock factor functions at the convergence of the stress response and developmental pathways in Caenorhabditis elegans.

Heat shock factor (HSF) is best characterized as the transcriptional regulator of heat shock protein genes, required by all cells to survive periods of stress. Recent evidence suggests that HSF also functions to regulate the expression of genes involved in growth and development under normal physiological conditions. In this study, we used RNA interference (RNAi) assays to investigate the role of HSF in Caenorhabditis elegans. Exposure of wild-type worms to hsf dsRNAi constructs caused a temperature-sensitive developmental arrest at the L2/L3 stage. At normal growth temperatures, hsf(RNAi) worms that developed to adults were small and scrawny, largely infertile, and showed a significant reduction in life span. These results demonstrate that HSF is required for normal postembryonic development under physiological conditions. Following heat shock, hsf(RNAi) worms were thermosensitive and displayed a significant reduction of hsp16 expression. When hsf(RNAi) was carried out in various dauer-constitutive mutant backgrounds, a dramatic reversal of dauer formation was observed, indicating that HSF is also required in the dauer pathway. In its natural habitat of the soil, where C. elegans is exposed to a constantly fluctuating environment; the ability to integrate the stress response with development may be an essential element of its ecology.