Entrainment of the Drosophila circadian clock by light

Abstract

The phenomenon of circadian (~24 h) rhythms has been conserved from single cell (e.g. cyanobacteria) to complex organisms including plants and mammals. Although the output varies from one species to another, ranging from the circadian production of asexual spores in Neurospora and the circadian movement of leaves in Arabidopsis to the rest:activity rhythm in Drosophila and mammals, all circadian rhythms share some basic properties 1) They can be synchronized or entrained to environmental cues such as light or temperature. 2) They freerun in constant conditions. 3) the periodicity is temperature compensated, i.e. the period does not change over a wide range of temperature. In addition, they are all thought to be produced by a circadian system that consists of an input pathway, a central clock and an output pathway. The clock is the timekeeping component that transmits its signals to the rest of the organism through the output pathway. The input pathway serves to connect the clock to the environment, conveying signals from external stimuli such as light and temperature. Much of our current understanding of how clocks are generated in mammals is derived from research done in the fruit fly Drosophila melanogaster. This chapter will focus on the molecular mechanisms that entrain the clock to light in this organism.