Worm Breeder's Gazette 16(1): 49 (October 1, 1999)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
|1||Biologie moleculaire et cellulaire, INRA biotechnologies, 78352 Jouy-en-Josas, France|
|2||Evolution du developpement des nematodes, Institut Jacques Monod, CNRS, Universite Paris 6/7, Tour 43, 2 pl. Jussieu, 75251 Paris, France|
Steroids control expression of a number of genes through activation of well characterized intracellular receptors that bind to specific responsive elements and act as transcription factors. However, in many cell types, increasing evidence emerges for steroid membrane targets, either G-protein coupled or neurotransmitter receptors, through which steroids might exert their "non-genomic" effects. Moreover, some steroid hormones are thought to influence animal communication and behaviour as external chemical signals, suggesting the existence of specific steroid chemosensory receptors. We examined chemotaxis responses of nematodes to different mammalian steroid compounds, including androgens, estrogens, their precursors cholesterol, pregnenolone and progesterone, as well as 5-b and 5-a-pregnanolone, two neurosteroids. In a preliminary screen for steroid attraction on round plate assays (as described by C. Bargman, 1993), all compounds were diluted in ethanol at a concentration of 10-5 M and ethanol considered as background. Amongst different nematodes, C. elegans N2 showed preference for progesterone and the estrogen class, C. briggsae was found strongly attracted to dihydroxytestosterone, while several androgens attracted Osheius (CEW1) and Panagrolaimus. Importantly, all nematodes chemotaxed to the two steroid precursors pregnenolone and cholesterol. Chemotaxis responses in different strains of C. elegans were then analysed in more details on square plate assays which allowed discrimination between attractive/repellent effects. As already described for other volatile odorants, responses were rarely linear with concentrations, attraction or repulsion can be observed for the same compound depending on dilution, effects being maximal for one given concentration of hormone (hook effects). The chemotaxis patterns for the two neurosteroids looked different with, between 10-3 M and 10-7 M, several attractive and several repulsive hormone concentrations. When several strains of C. elegans were compared, differences in chemotaxis behaviour to some steroids (progesterone or testosterone) were sufficient to allow genetic analysis of the response. Finding exogenous steroid precursors might be essential for nematode development and physiology, and our observations suggest the presence of olfactory receptors for this class of compounds. However one cannot exclude that attraction to certain steroid hormones (especially to the neurosteroid class) might not involve only olfactory receptor neurones.