European Conference on Nematode Neurobiology location:Cambridge date:21-23 September
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 the existence of circadian rhythms in the nematode Caenorhabditis elegans in the year 2002, none of the “classical” circadian clock homologues, such as lin-42 (~period) and tim-1 (~timeless) genes, have been linked to the C. elegans clock. Until now, they are only proven to be involved in the timing of development rather than the regulation of circadian rhythms. Our lab has recently discovered three pigment dispersing factor (PDF)-like neuropeptides and three PDF receptor homologues in C. elegans. Since PDF is considered to be the key output signal between the internal circadian clock and rhythmic behaviour in the fruit fly Drosophila melanogaster, the question was raised as to whether or not these peptides and receptors are involved in the C. elegans clock. To study this, we implemented the Goodman parallel worm tracker to measure the average movement speed of populations of different strains over several days. In contrast to 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 in circadian locomotor rhythms 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 even lose their rhythmicity after three days in constant dark conditions. This does not necessarily rule out the involvement of PDF in the C. elegans clock, as pdf-2 and pdfr-1 mutants remain to be tested. Currently, we are screening a mutagenized C. elegans library for pdf-2 and pdfr-1 deletion mutants and are analysing circadian rhythms in pdf-1 and “classical” clock homologue mutants.