Meeting Abstract
Circadian clocks are well understood in many bilaterian organisms where they regulate behavior and physiology through differential expression of hundreds of genes over daily and seasonal time. However, we have a rudimentary understanding of the antiquity and function of these clocks for earlier diverging lineages, including cnidarians. The sea anemone, Nematostella vectensis, is an emerging model for cnidarian circadian biology and previous studies have demonstrated rhythmic behavior that coincides with light-dependent expression of candidate circadian genes. To further characterize the role light plays in entraining circadian rhythms in this species, we used tag-based RNAseq to generate 136 transcriptomes from animals sampled over three days during four light regimes (12h:12h light:dark, 1 and 2 days post light-removal, and constant darkness) treated as ‘light conditions’. Weighted gene co-expression network analysis identified unique co-regulated gene modules differentially expressed between all light conditions. In the first 24-hour period of light removal, N. vectensis exhibited a 3-fold increase in the number of differentially expressed genes, particularly those involved in chromatin organization, as well as key members of the oxidative stress and metabolic pathways. Additionally, genes previously described as ‘circadian’ were down-regulated in the absence of light and appear to lose rhythmicity immediately following light removal. Interestingly, the second day of light removal resulted in an entirely new set of differentially expressed genes compared with other light conditions. These data highlight the molecular complexity resulting from photoperiodic variability and, for the first time in cnidarians, suggests genes commonly referred to as ‘circadian’ may be better described as photoresponsive.
