Transcriptional remodeling upon light removal in a model cnidarian: losses and gains in gene expression

Organismal responses to light:dark cycles can result from two general processes: (i) direct response to light or (ii) a free-running rhythm (i.e., a circadian clock). Previous research in cnidarians has shown that candidate circadian clock genes have rhythmic expression in the presence of diel lighting, but these oscillations appear to be lost quickly after removal of the light cue. Here, we measure whole-organism gene expression changes in 136 transcriptomes of the sea anemone Nematostella vectensis, entrained to a light:dark environment and immediately following light cue removal to distinguish two broadly defined responses in cnidarians: light entrainment and circadian regulation. Direct light exposure resulted in significant differences in expression for hundreds of genes, including more than 200 genes with rhythmic, 24-hour periodicity. Removal of the lighting cue resulted in the loss of significant expression for 80% of these genes after one day, including most of the hypothesized...