The neuropeptide FMRFamide (Phe-Met-Arg-Phe-NH2) is a member of a large family of related peptides that have been found throughout the animal kingdom. By using an antiserum specific for the Arg-Phe-NH2 moiety, we have found that about 10% of the neurons in the nematode Caenorhabditis elegans are immunoreactive. Most of these neurons, which include sensory, motor, and interneurons, were identified on the basis of their number, position, and projection pattern and by analysis of characterized mutants. Neurons that were immunoreactive in hermaphrodite animals were generally also found in males, but each sex had, in addition, sex-specific immunoreactive cells. Staining of hermaphrodite animals from different larval stages suggests that the onset of FMRFamide-like expression is differentially regulated among the cells. We have found a possible neuromodulatory role for the related peptide FLRFamide (Phe-Leu-Arg-Phe-NH2). In an egg-laying assay, FLRFamide by itself was not active but could potentiate a serotonin effect. The FMRFamide-like immunoreactivity was also used as a marker to examine the differentiation of cells that normally undergo programmed cell death. Cells that are destined to die in the Pn.a lineages appear to differentiate and adopt the fate of lineally equivalent cells before cell death.

In order to assist in the identification of possible endocrine disrupting chemicals (EDC) in groundwater, we are developing Caenorhabolitis elegans as a high throughput bioassay system in which responses to EDC may be detected by gene expression using DNA microarray analysis. As a first step we examined gene expression patterns and vitellogenin responses of this organism to vertebrate steroids, in liquid culture. Western blotting showed the expected number and size of vitellogenin translation products after estrogen exposure. At 10−9 M, vitellogenin decreased, but at 10−7 and 10−5, vitellogenin was increased. Testosterone (10−5 M) increased the synthesis of vitellogenin, but progesterone‐treated cultures (10−5 M) had less vitellogenin. Using DNA microarray analysis, we examined the pattern of gene expression after progesterone (10−5, 10−7, and 10−9 M), estrogen (10−5 M), and testosterone (10−9 M) exposure, with special attention to the traditional biomarker genes used in environmental studies [vitellogenin, cytochrome P450 (CYP), glutathione s‐transferase (GST), metallothionein (MT), and heat shock proteins (HSP)]. GST and P450 genes were affected by estrogen (10−5 M) and progesterone (10−5 and 10−7 M) treatments. For vitellogenin genes, estrogen treatment (10−5 M) caused overexpression of the vit‐2 and vit‐6 genes (2.68 and 3.25 times, respectively). After progesterone treatment (10−7 M), the vit‐5 and vit‐6 were down‐regulated and vit‐1 up‐regulated (3.59‐fold). Concentrations of testosterone and progesterone at 10−9 M did not influence the expression of the vit, CYP, or GST genes. Although the analysis is incomplete, and low doses and combinations of EDC need to be tested, these preliminary results indicate C. elegans may be a useful laboratory and field model for screening EDC.

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