Hydroxysteroid dehydrogenase involved in the biosynthesis of dafrachonic acids (PubMed:18495818, PubMed:20178781, PubMed:24411940). Catalyzes the dehydrogenation of cholesterol or its derivatives and the isomerization of the double carbon bond on the sterol ring. Modifies sterols into a Delta(4)-3-keto-sterols such as cholest-4-en-3-one, precursor of Delta(4)-dafachronic acid (PubMed:18495818). Contributes to the production of Delta(7)-dafachronic acid in the XXX cells (PubMed:24411940). Dafachronic acids act as ligands and bind directly to the nuclear hormone receptor (NHR) daf-12 suppressing dauer formation and inducing reproductive growth (PubMed:18495818, PubMed:24411940). Acts in parallel to AKT-1 to promote reproductive development via DAF-16/FoxO and DAF-12 (PubMed:20178781). a 3beta-hydroxy-Delta(5)-steroid + NAD(+) = a 3-oxo-Delta(5)-steroid + H(+) + NADH cholesterol + NAD(+) = cholest-5-en-3-one + H(+) + NADH a 3-oxo-Delta(5)-steroid = a 3-oxo-Delta(4)-steroid cholest-5-en-3-one = cholest-4-en-3-one Steroid hormone biosynthesis; dafachronic acid biosynthesis. Expressed exclusively in the neuron-like XXX(L/R) cells through all four larval stages and becomes fainter in adults. Mutants are hypersensitive to pheromone induction and form dauers more readily than the wild-type. Belongs to the 3-beta-HSD family. Although thought to contribute to D(4)-dafrachronic acid biosynthesis, the latter may not be present at physiologically relevant concentrations in C.elegans and comparative metabolomics would indicate 7-dehydrogenase activity and participation in D(7)-dafrachronic acid biosynthesis instead.