Abstract
Transcriptional profiling experiments identify light- and temperature-entrained circadian transcripts in
C. elegans
.
Most organisms have an endogenous circadian clock that is synchronized to environmental signals such as light and temperature. Although circadian rhythms have been described in the nematode
Caenorhabditis elegans
at the behavioral level, these rhythms appear to be relatively non-robust. Moreover, in contrast to other animal models, no circadian transcriptional rhythms have been identified. Thus, whether this organism contains a bona fide circadian clock remains an open question. Here we use genome-wide expression profiling experiments to identify light- and temperature-entrained oscillating transcripts in
C. elegans
. These transcripts exhibit rhythmic expression with temperature-compensated 24-h periods. In addition, their expression is sustained under constant conditions, suggesting that they are under circadian regulation. Light and temperature cycles strongly drive gene expression and appear to entrain largely nonoverlapping gene sets. We show that mutations in a cyclic nucleotide-gated channel required for sensory transduction abolish both light- and temperature-entrained gene expression, implying that environmental cues act cell nonautonomously to entrain circadian rhythms. Together, these findings demonstrate circadian-regulated transcriptional rhythms in
C. elegans
and suggest that further analyses in this organism will provide new information about the evolution and function of this biological clock.
Daily (circadian) rhythms in behavior and physiology allow organisms to adapt to periodic cues such as light and temperature associated with the rotation of the earth. Subsets of molecular components of the internal clock that drive these rhythms, as well as effector genes for behavioral outputs, also exhibit rhythmic expression in many organisms. While circadian rhythms in behavior have previously been described in the nematode
Caenorhabditis elegans
, no transcriptional rhythms or clock genes have been identified, leaving open the question of the nature of the clock in this organism. Here, we identify light- and temperature-entrained cycling genes in
C. elegans
via genome-wide transcriptional profiling. Transcripts showing circadian regulation (including expression with a 24-h period maintained upon removal of the entraining stimulus) and temperature compensation were identified. Light and temperature appear to entrain independent sets of genes. We also identify large sets of light- or temperature-driven genes. Mutations in a channel gene previously implicated in sensory transduction in a small set of sensory neurons abolish entrainment of gene expression by environmental signals. This work demonstrates the presence of circadian transcriptional rhythms in
C. elegans
, and provides the foundation for future investigations into the underlying mechanisms.