Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Abstract Only
Publication Acceptance Date: March 13, 2006
Publication Date: June 5, 2006
Citation: Chitwood, D.J., Skantar, A.M. 2006. Clues to sterol function in nematodes: recent studies with Caenorhabditis elegans and the soybean cyst nematode [abstract]. 97th American Oil Chemists' Society Annual Meeting (Abstracts). p. 21.
Nematodes possess a nutritional requirement for sterol because of their inability to biosynthesize sterols de novo. Consequently, parasitic nematodes must obtain sterols from their hosts and then metabolize them to other sterols and steroids required for nematode growth, development and reproduction. This nutritional dependency and nematode-specific steroid metabolic pathways provide attractive targets for disrupting the life cycles of these parasites. We have performed several investigations utilizing Caenorhabditis elegans as a model organism for studying sterol biochemistry in plant-parasitic nematodes. The most notable sterol metabolic transformation performed by C. elegans is the introduction of a methyl group at C-4 on the sterol nucleus by a pathway seemingly unique to nematodes. Like insects, C. elegans can remove the methyl or ethyl substituents present at the C-24 position of the sterol side chain, and the delta-24-sterol reductase involved can be inhibited by 25-azacoprostane. Unlike insects, C. elegans does not appear to synthesize ecdysone or related insect hormones. The C. elegans let-767 gene encodes a protein similar to mammalian enzymes that reduce 17-beta-hydroxysteroids. We have identified two homologues of let-767 in the soybean cyst nematode, Heterodera glycines. These genes, Hg-hsd-1 and Hg-hsd-2, share similarity to 17-beta-hydroxysteroid dehydrogenases involved in the synthesis of steroid hormones in mammals. Quantitative real-time PCR revealed the highest expression of both genes in developing female H. glycines, with relatively low levels in second-stage juveniles, eggs, or males. These 17-beta-hydroxysteroid dehydrogenases may be involved in the conversion of sterols into nematode steroid hormones.