Circadian rhythms identified inCaenorhabditis elegansby in vivo long-term monitoring of a bioluminescent reporter

Abstract

Circadian rhythms are based on endogenous clocks that allow organisms to adjust their physiology and behavior by entrainment to the solar day and, in turn, to select the optimal times for most biological variables. Diverse model systems—including mice, flies, fungi, plants, and bacteria—have provided important insights into the mechanisms of circadian rhythmicity. However, the general principles that govern the circadian clock ofCaenorhabditis eleganshave remained largely elusive. Here we report robust molecular circadian rhythms inC.elegansrecorded with a bioluminescence assay in vivo and demonstrate the main features of the circadian system of the nematode. By constructing a luciferase-based reporter coupled to the promoter of the suppressor of activatedlet-60Ras (sur-5) gene, we show in both population and single-nematode assays thatC.elegansexpresses ∼24-h rhythms that can be entrained by light/dark and temperature cycles. We provide evidence that these rhythms are temperature-compensated and can be re-entrained after phase changes of the synchronizing agents. In addition, we demonstrate that light and temperature sensing requires the photoreceptors LITE and GUR-3, and the cyclic nucleotide-gated channel subunit TAX-2. Our results shed light onC.eleganscircadian biology and demonstrate evolutionarily conserved features in the circadian system of the nematode.