S7-2.4 Sunday, Jan. 6 The monarch butterfly reveals the prototype ancestral TTFL clock of insects: a focus on cryptochromes REPPERT, SM; UMass Medical School, Worcester Steven.Reppert@umassmed.edu
In Drosophila and mammals, the classic clock mechanism is comprised of a core negative transcriptional/translational feedback loop (TTFL), which drives self-sustaining rhythms of essential clock components. The monarch butterfly (Danaus plexippus) core feedback loop possesses all the critical clock genes found in Drosophila— clock (clk), cycle (cyc), period (per), timeless (tim), and type-1 cryptochrome (designated cry1) —but differs in that it also possesses a type-2 vertebrate-like cry (cry2), which encodes the main transcriptional repressor in the monarch clock, a function fulfilled by per in Drosophila, which does not possess cry2. The discovery of type-2 vertebrate-like CRYs in insects, derived from the discovery of CRY2 in monarchs, has profoundly altered our view of how circadian clocks of non-drosophilid insects work. To further our understanding of animal clock evolution, we reinvestigated the existence of type-1 and type-2 CRYs in all arthropods in which a draft genome has been published. All possess a type-2 CRY, except for all Drosophila species, which only possess the light-sensitive type-1 CRY. This supports the existence of both CRY types at the base of arthropod evolution. In addition, type-1 CRY and TIM appear to have been lost prior to the radiation of the hymenopterans, suggesting that the Hymenoptera have evolved different mechanism(s) for photic entrainment. Perhaps the TIMELESS paralog, TIMEOUT, which has some influence on the light input pathway in Drosophila, is the key, as it is expressed in all available insect genomes.