CIRCADIAN RHYTHMS IN C. elegans: LOCOMOTOR ACTIVITY, METABOLISM AND STRESS

Introduction: C. elegans is a model organism widely used in diverse areas of research but not well characterized in chronobiological studies. We have recently designed an automated system to track individual nematodes and demonstrated the existence of circadian activity rhythms in both LD (light : dark, 12 h : 12 h) and DD (constant darkness) conditions, periods were found to be of 24.2±0.44 h and 23.1±0.40 h respectively. In addition, circadian periods were temperature-compensated and could also be entrained by temperature cycles. Mutations in clock gene homologs induced circadian phenotypes with altered periodicities. Methods: In order to determine if the worms are able to detect different light wavelengths, we have studied phototaxic responses, and found a phototaxis index of 0.7 ± 0,09 towards the green wavelength of light (520nm). Another approach to uncover rhythmic outputs was the study of stress tolerance behaviors. We found that C. elegans showed rhythmic stress tolerance patterns for oxidative and osmotic stress with peaks at ZT 12 (lights on) and ZT 0 (lights off), respectively. Stress-related gene expression was determined by sqRT-PCR and confirmed by RealTime-PCR: gpdh-1 and gpx showed a significant diurnal variation. We have also studied circadian rhythms in metabolic variables, such as food consumption and defecation. Results: Food consumption rate (determined by decreasing OD600 of E. coli OP50) was shown to be rhythmic and a peak was found in the evening (ANOVA, p <0.0001). Defecation rhythms also showed to be governed in a circadian manner. These results show that control animals have a 24 h period in the frequency of the ultradian defecation rhythm (ANOVA, p < 0.0001). Furthermore, the defecation behavior of the JT73 mutant strain depicts a normal rhythmic pattern on a circadian level (ANOVA, p <0.01). Finally, we have detected aaNAT activity and melatonin in this nematode. aaNAT exhibited a diurnal variation peaking at ZT12, and melatonin could serve as a possible circadian output signal. Conclusion: In summary, our results show that several different circadian outputs can be recorded in C. elegans ; in particular, the circadian rhythm of locomotor activity can be entrained to environmental signals. These data might be a basis for the screening of putative circadian mutants in this species. Publication History Article published online: 16 June 2026 © 2009. Brazilian Sleep Academy. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Thieme Revinter Publicações Ltda. Rua Rego Freitas, 175, loja 1, República, São Paulo, SP, CEP 01220-010, Brazil