Cellular and molecular mechanisms of circadian control in insects

Genetic analysis in Drosophila melanogaster has identified molecules important for the function of insect circadian clocks, and this has resulted in the elaboration of explicit biochemical models of the clock mechanism. Comparable molecular genetic analysis coupled with neuroanatomical approaches has also delineated cellular elements of the circadian pacemaker controlling insect activity rhythms. However, not much is known about the transfer of temporal information from clock cells in the insect brain to downstream neural elements or other target cells that are regulated by the clock (i.e. clock output pathways). In this review, we focus on the insect literature, with special reference to the fruitfly D. melanogaster and the hawkmoth Manduca sexta, to discuss the candidate molecules, biochemical mechanisms and cell types implicated in the clock control of behavior.