3177 311 zyxwvuts NOVEL NUCLEAR METHYLATION OF STEKOLS BY THE NEMATODE CAENORHABDITIS ELEGANS David J. Chitwood, William R. Lusby, Ruben Lozano, Malcolm J. Thompson, and James A. Svoboda Insect Physiology Laboratory Beltsville Agricultural Research Center II. S. Department of Agriculture Beltsville, Maryland 20705 Received zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHG 10-7-83 ABSTRACT Caenorhabditis elegans possesses a unique sterol methylation pathway not reported to occur in any other organism and also removes the C-24 ethyl group of sitosterol (a plant sterol). This nematode produced substantial quantities of 4a-methyl-5a-cholest-8(14)-en-3e-o1 and smaller amounts of lophenol from dietary cholesterol, desmosterol or sitosterol. When C. elegans was propagated in media containing sitosterol plus 2%azacoprostane h drochloride (25-aza-5~-cholestane hydroch?oride), an inhibitor of zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONM A 23; -sterol reductase in insects, its 4a~ethylsterol fraction largely consisted of equal amounts of 4a-methyl&-cholesta-7,24-dien-36-01 and 4a-methyl-tia-cholesta- 8(14),24-dien-38-01. Thus 25-azaco rostane both a A24-sterol reductase and a A “z hydrochloride inhibited -sterol isomerase in C. elegans. INTRODUCTION The free-living nematode Caenorhabditis elegans has become an important tool for investigation of metazoan genetics, developmental biology, and biochemistry [I]. The nutritional requjrement for sterol in nematodes as well as the lack of de novo biosynthesis has been well -- established [2-61. Phytophagous insects also require dietary sterol; most produce cholesterol via removal of the side chain C-24 methyl and ethyl groups typical of C28 and C2g plant sterols [7]. We initially propagated C. elegans in a medium containing sitosterol (24a-ethyl-5-cholesten-3e-ol) to determine if it possesses a similar dealkylation pathway. Surprisingly, we found that 2. elegans not only removed the substituent at C-24 but also converted a Volume 42, Number 3 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIH S TIEIICOXD= September 1983