CRY2 genetic variants associate with the depressive episodes in a range of mood disorders. Expression of core clock genes is highly responsive to stimuli in brown fat. Brown fat clocks might synchronize clocks in other tissues through their control of heat production and core body temperature. Among the repressors within the clocks, CRY2 is hypothesized to a key to the resetting of clocks throughout and play a leading role in the antidepressant effect of total sleep deprivation.