C.elegans can not synthesize cholesterol de novo but sterols are absolutely required for worm development. Cholesterol auxotrophy makes the worm a valuable system for studying sterol metabolism and functions by replacing dietary cholesterol with different derivatives and analogs. As a starting point for our investigation on the role of sterols in C.elegans, we developed a protocol for complete elimination of sterols in the medium and food. After one generation, strict sterols depletion caused uniform arrest into a dauer-like larvae with incomplete molting. Studying the metabolism of cholesterol under the conditions of cholesterol depletion indicated reduced levels of nonmethylated sterols and accumulation of 4-alpha methylated sterols. This prompted us to test how the methylated sterols influence dauer formation. Substitution of cholesterol by the 4-alpha methylated sterol lophenol was sufficient to complete dauer larva formation in the second generation. However, our data indicate that methylated sterols do not actively induce the dauer formation but rather that the reproductive growth requires a cholesterol derived hormone that can not be produced from methylated sterols. Using the effect of lophenol on growth, we have partially purified activity, named gamravali, which promotes the reproduction. In addition, effect of lophenol allowed us to identify the step at which gamravali is required during the reproductive development. In the absence of gamravali, the nuclear hormone receptor DAF-12 is activated and triggers dauer formation program by allowing in neurons the nuclear import of DAF-16, a forkhead domain (FOXO) transcription factor required for dauer formation. Our results reveal a novel function of DAF-16 downstream of DAF-12 in order to complete dauer differentiation. Reference: Matyash V, Entchev EV, Mende F, Wilsch-Brauninger M, Thiele C, Schmidt AW, Knolker, HJ, Ward, S, Kurzchalia, TV. Sterol-Derived Hormone(s) Controls Entry into Diapause in Caenorhabditis elegans by Consecutive Activation of DAF-12 and DAF-16. PLoS Biol, 2004. 2(10): p.
e280.