Investigating the Function of the bHLH CLOCK in Nematostella vectensis

The biological clock, an internal oscillator that helps organisms to maintain rhythmicity and anticipate changes, has been extensively studied in model organisms such as mice and flies. Recently, this oscillator has also been identified in cnidarians, which exhibit several rhythmic phenomena that are either directly or indirectly cued by environmental stimuli, including light. Despite sharing homologs of putative core clock genes with bilaterians, the connections between light-dependent behaviors and molecular responses in cnidarians remain indefinite. In this study, we used behavioral monitoring and transcriptomic analysis of a CRISPR/Cas9 generated mutant to investigate the circadian function of the bHLH transcription factor CLOCK in Nematostella vectensis, a cnidarian model species. We found that clock is required to maintain the rhythm of behavior under free-running conditions and for the rhythmicity of most clock-controlled genes, but not for the oscillator itself. These findings suggest that the biological clock in cnidarians has evolved to extend the connection between the oscillator and the organism, simplifying the interaction with the environment.