Meeting Abstract
Cnidarians exhibit diel rhythms including cycles in locomotor activity, tentacle extension, and spawning. Behavioral and molecular studies conducted in corals and the anemone Nematostella vectensis suggest the presence of an endogenous circadian clock. Nematostella inhabits shallow estuarine habitats that can experience strong diel and/or tidal cycles in light, temperature and water chemistry, so we sought to characterize rhythmic gene expression within Nematostella exposed to natural field conditions. Anemones from the lab were incubated within mesh cages in a tidal pool in Sippewissett Marsh, the site from which the lab population was derived. After two weeks, animals were recovered, sampled every two hours over a 24-hour period (12-hour light/dark), and characterized using RNA-seq. Rhythmic genes were identified using the R-package JTK_CYCLE. These data indicate that a large number of genes undergo a diel cycle in expression (3813 genes/22.7% of the filtered transcriptome with an adjusted p-value <0.05), compared with only 365 genes exhibiting a 12-hour tidal cycle. Many genes previously identified as cyclic in Nematostella (Clock, Hes/Hey-like, heat shock proteins, protein disulfide isomerase) were confirmed as cyclic in this study. Surprisingly, the rhythmic genes were heavily biased toward daytime peaks in expression. In addition, approximately 160 of the rhythmic genes have also been shown to be directly inducible by UV exposure in Nematostella. This study indicates that natural field conditions stimulate large daily cycles in gene expression, which are greatly reduced under more constant laboratory conditions used in previous studies. Despite the burrowing behavior of the anemones, light appears to remain an important driver of gene expression and physiology.
