The eicosanoids, which include prostaglandins (PGs), leukotrienes and thromboxanes, are signaling molecules derived from polyunsaturated fatty acids, or PUFAs. In mammals, eicosanoids are implicated as regulators of inflammation, immunity, reproduction, and central nervous system function. We have shown that C. elegans oocytes generate PUFA-derived sperm-attracting signals. An RNAi screen for non-autonomous regulators of sperm guidance identified two predicted PG synthases, K08F4.7 and R11A8.5. Wild-type sperm in K08F4.7 null hermaphrodites have reduced velocity and directional velocity and increased reversal frequency. Indomethacin, an inhibitor of mammalian PG synthesis, causes mild sperm guidance defects. Microinjecting human D, E, and F-series PGs, which are structurally similar, into PUFA-deficient gonads stimulates sperm velocity. These results suggest that PGs mediate sperm guidance. To identify worm eicosanoids, we developed a profiling method using 27 eicosanoid standards and liquid chromatography coupled to electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). Analysis of retention times, parent ions, and collision-induced decomposition patterns from wild-type extracts shows that C. elegans produces a wide range of novel PGs, mostly of the F-series.
fat-3 mutants, which are deficient in C20 PUFA production, have decreased, but not completely absent PG levels. Comparative profiling of several targeting-defective mutants suggests that multiple F-series PGs control sperm motility. Mutation of the delta-12 desaturase
fat-2 causes a major reduction in C18 and C20 PUFAs. However, LC-ESI-MS/MS analysis of
fat-2(
wa17) extracts shows that these mutants generate significant amounts of many PGs. We show that
fat-2 mutants upregulate a compensatory mechanism dependent on the FOXO transcription factor DAF-16, which controls the expression of fat genes and numerous other genes implicated in eicosanoid metabolism (Murphy et al. 2003). Loss of
fat-2 causes increased DAF-16 activation, which is reversed by PUFA supplementation. Basal DAF-16 activity in the germ line is critical for correct sperm targeting, yet increased DAF-16 activity, as observed in
daf-2 insulin receptor mutants,
fat-2(
wa17) mutants, and starved animals, causes severe sperm guidance defects. Collectively, we have evidence for two classes of DAF-16-dependent targets, those that mediate the synthesis of eicosanoids important for survival and germline development and those that inhibit the F-series PG function required for sperm guidance.