I came across a PLoS article today suggesting that the Sea Anemone, the last common ancestor of Cnidaria and Bilateria, has more circadian clock machinery comparable to its more primitive ancestors than previously thought.
Woods Hole Researchers have characterized circadian expression in photic-sensitive genes, such as CLOCK and CRY, using varied light spectrums: solely blue light, normal trichromatic light, blue-deficient light, and of course, constant darkness as a control. Not surprisingly, CLOCK, a photosensitive circadian gene, had potentiated and rhythmic expression in response to blue (high-energy light) and trichromatic light, moderate expression under blue-deficient light, and as anticipated, minimal expression in constant darkness. CLOCK expression peaked near the end of lights-on, much like other circadian photosensitive genes such as the Pers.
The researchers also elucidated heterodimerization between CLOCK and CYCLE. Heterdimerization of translated proteins from circadian genes is a critical component of the molecular feedback loop that stabilizes endogenous circadian pacemaking. Once heterodimerization occurs, it can then regulate the transcription of other positive (increased expression) or negative (decreased expression) transcribable circadian genes.
Overall, I believe that this is an excellent approach towards elucidating the phylogenies of the circadian timing systems in both vertebrates and invertebrates.
As a side note, I envy the person who collected these Sea Anemone specimens for analysis…..ah ocean……god, do I hate being so frackin landlocked!
Adam M. Reitzel, Lars Behrendt, Ann M. Tarrant* (2010). Light Entrained Rhythmic Gene Expression in the Sea Anemone Nematostella vectensis: The Evolution of the Animal Circadian Clock PLoS ONE