A wide variety of organisms use an internal biological clock to adapt their lifestyle to the periodically changing environment. A circadian clock has a period of 24 hours and controls a day- and night rhythm in behaviour and biochemistry. Since the first publication of a circadian clock in the nematode Caenorhabditis elegans in the year 2002, none of the "classical" circadian clock homologues, such as the period and timeless genes, could be linked to this worm''s clock. Until now, they are only proven to be involved in the developmental rhythm rather than the circadian rhythm of C. elegans. With our discovery of three pigment dispersing factor (PDF) peptides and three receptor homologues in C.elegans, the question raised as to whether or not these peptides and receptors are involved in the C. elegans clock, since PDF is considered to be the key output signal between the internal circadian clock and rhythmic behaviour in the fruit fly Drosophila melanogaster. We implemented the Goodman parallel worm tracker to measure the average movement speed of populations of different strains over several days. In contrast with previously described experiments, we succeeded in showing circadian rhythmicity in the activity of wild type nematodes under standard culture conditions (NGM plates with Escherichia coli OP50 as food source). In addition, rapid overgrowth of plates due to offspring was avoided without the use of FUDR or RNAi. As previously described, the activity of wild type nematodes is higher during the day compared to the night and this rhythm persists under constant dark conditions. Preliminary observations of
pdf-1 mutants showed no clear aberrations except for an overall lower speed and higher percentage of non-moving individuals compared to wild type nematodes. These results do not resemble the behaviour of pdf mutant fruit flies, which lose their morning activity peak, show an advanced evening activity peak and which lose their rhythmicity after three days in constant dark conditions. This does not necessarily rule out the possible involvement of PDF in the C. elegans clock, as
pdf-2 and
pdfr-1 mutants remain to be tested. Currently, we are analysing circadian rhythms in
pdf-1 and "classical" clock mutants.