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.

Steroid hormones as volatile odorants for Caenorhabditis elegans and other nematodes.

Remy JJ1, Felix MA2

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.