Submitted to: Journal of Lipid Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 16, 2002
Publication Date: N/A
Interpretive Summary: Plant-parasitic nematodes are microscopic worms that attack plant roots and annually cause U.S. crop losses of nearly ten billion dollars. One problem in controlling nematodes is that the few available chemicals are far from perfect with respect to environmental and human safety. One approach to developing new methods for nematode control is by exploiting major differences between nematode and host plant biochemistry. Previous ARS research revealed that one of the few biochemical differences between plants and nematodes is that nematodes cannot make compounds called sterols. Nematodes must obtain them from host plants and convert them to other sterols such as cholesterol and remarkable nematode-unique sterols. In this paper, ARS collaborators and an ARS scientist examined the ability of different sterols to satisfy the nutritional requirement for sterol in nematodes, and they also determined the anatomical location of sterols. The most interesting discoveries were that cholesterol and the nematode- unique sterols have different functions within nematodes, and that sterols accumulate in only five specific cells in nematodes. The results are significant because they provide the first evidence that the nematode- unique sterols have different roles than sterols usually have in animals and plants. This information will be used by scientists developing safe methods for controlling plant-parasitic nematodes.
The nematode Caenorhabditis elegans is unable to synthesize the sterol ring and requires dietary sterol for unknown functions. In this study, we demonstrate that larval growth and development require sterol at numerous stages, perhaps continuously. Egg-laying was abolished in the second generation of cholesterol deprivation, but the presence of only 10 ng/ml cholesterol resulted in the delayed laying of a small number of normal eggs. Eggs laid by animals grown under sterol-free conditions, or on sterols other than cholesterol, always hatched normally. Several desmethyl sterols differing from cholesterol in double bond number and placement substituted completely for cholesterol, but vertebrate or insect steroid hormones could not. Two 4-methylsterols differing only in double bond placement, both unique metabolites found in C. elegans, provided limited growth promoting activity when used alone. However, the addition of minute amounts of cholesterol (10 ng/ml, or 1% of the amount of 4-methylsterol) was highly synergistic, restoring nearly normal levels of growth and egg-laying. Filipin staining indicated that the nematodes accumulate sterols in five specific cells: two amphid socket cells, two phasmid socket cells and the excretory gland cell. The pharynx and intestinal epithelium were stained by filipin in an anterior-to-posterior gradient and are apparently the sites of sterol uptake. We conclude that at least two different sterols are required to perform discrete functions.