Abstract
Circadian rhythms of behavior, physiology, and gene expression are present in diverse tissues and organisms. The function of the transcriptional activator,
Clock, is necessary in both
Drosophila and mammals for the expression of many core clock components. We demonstrate in
Drosophila that
Clock misexpression in naı̈ve brain regions induces circadian gene expression. This includes major components of the pacemaker program, as
Clock also activates the rhythmic expression of
cryptochrome, a gene that CLOCK normally represses. Moreover, this ectopic clock expression has potent effects on behavior, radically altering locomotor activity patterns. We propose that
Clock is uniquely able to induce and organize the core elements of interdependent feedback loops necessary for circadian rhythms.