In the field of chronobiology, it has been understood for some time that food intake is an important timing cue (a ‘zeitgeber’) for the circadian clock. This has led to hypotheses about how the deleterious effects of mistimed meals, or erratic eating patterns (during shift work, for example), might come about. However, the mechanism by which feeding entrains the clock has proved elusive.

Now, using mouse and in vitro studies, Crosby et al. have shown the importance of insulin and the insulin signalling pathway for resetting the clock. Insulin signalling leads to the induction of PERIOD proteins, which are an important component of the negative feedback loop of the molecular clock. Interestingly, the suprachiasmatic nucleus of the hypothalamus, which receives input from the retinohypothalamic tract and thus co-ordinates organismal rhythms with the light−darkness cycle, was found to be more resistant to the effects of insulin than peripheral tissues. For mice kept in constant darkness, however, delivery of ‘mistimed’ insulin had significant enough effects on the clock to disrupt patterns of activity onset, highlighting the importance of insulin signalling as a zeitgeber.

Read the full article in Cell 177 896−909