The human NPC1 gene encodes an active membrane transporter of fatty acids and other hydrophobic molecules. Mutation in this gene causes Niemann-Pick disease, characterized by inappropriate lipid (especially cholesterol) accumulation. Deletion of the homologous C. elegans gene,
npc-1, caused hypersensitivity to cholesterol deprivation1. Cholesterol (delta 5 sterol) is metabolized by C. elegans to 7-dehydrocholesterol(7DHC; delta 5,delta 7 sterol), lathosterol (delta 7 sterol) and two 4alpha-methylsterols (4MS), through a pathway that may include, or lead to, one or more functionally active, required sterols. Either 7DHC or lathosterol can completely replace cholesterol to support C. elegans growth and reproduction, but 4MS's can do so only partially2,3. We have determined the responses of
npc-1 null animals to minimum levels of cholesterol, 7DHC, lathosterol and 4MS's. Compared with wild-type,
npc-1 null animals required ca. 3-fold higher levels of all sterols to achieve comparable growth and reproductive effects. Thus, the
npc-1 null phenotype could not be suppressed by replacement of cholesterol with any of its most abundant metabolites. We have previously shown by filipin staining that sterol accumulates in five distinct cells of cholesterol-grown C. elegans -two amphid socket cells, two phasmid socket cells and the excretory gland cell-and is also found in the intestine3. We now report that filipin stains the same five cells in chitinized embryos, which have never had an opportunity to ingest sterol. Intestinal staining is also seen, but is much weaker than in foraging animals. Animals raised on 7DHC or lathosterol stain similarly to those grown on cholesterol. The same five cells are stained to comparable intensity in cholesterol-grown
npc-1 null animals. Sterol accumulation patterns in
npc-1 null animals and embryos grown on 7DHC and lathosterol will also be presented. 1Sym et al., Curr. Biol. 10, 527, 2000; 2Lozano et al., Lipids, 22, 84,1987; 3Merris et al., in revision.