Molecular mechanism of circadian rhythmicity Circadian rhythmiclty is a consequence of intracellular molecular mechanisms involving so-called clock genes. The products of some of these clock genes regulate their own expression, and the outcome of this feedback loop is an oscillation in the levels of messenger ribonucleic

acids (mRNAs) and proteins. These mRNA and protein rhythms are observed in the suprachiasmatlc nucleus (SCN) of the hypothalamus, the master clock, as well Inhibitors,research,lifescience,medical as in other brain regions and peripheral tissues. Within the clock, other factors control the phosphorylation, stability, and localization of clock proteins, thereby regulating the oscillation, particularly the period. In mammals, Clock and Bmall encode transcription factors CLOCK and BMAL1 (brain and muscle ARNT-like protein 1; also known as ARNTL or MOP3),2-4 which form heterodlmers Inhibitors,research,lifescience,medical that activate the transcription of three Period genes (PER1, 2 and 3) and two Cryptochrome genes (CRY1 and 2),5-7 Rorαm and Rev-Erbα 8-10 (Figure 1). PER and CRY proteins form complexes11 that are translocated back into the nucleus and inhibit their own expression.5,7,12-15 RORα and REV-ERBα act on Bmall to activate and repress transcription respectively8,9 NPAS2 is an alternate dimerization partner for BMAL1 that may also regulate circadian

rhythmiclty in the see more forebraln, Inhibitors,research,lifescience,medical but it has not been consistently found in the SCN.16,17 Clock proteins are phosphorylated by casein kinase I epsilon (CKIε) and delta (CKIδ), and possibly also by the Drosophila shaggy homologue glycogen synthase kinase 3 (GSK3).18 They are targeted for degradation by components of ubiqultin llgase complexes like Inhibitors,research,lifescience,medical FBXL3 and β-TRCPl,19,20 which together regulate Inhibitors,research,lifescience,medical the period of circadian oscillation by controlling the rate of accumulation, association and translocation of PER and CRY.11,15,21-23 Figure 1. Simplified schematic diagram

of the molecular mechanisms of the circadian clock in mammals. See the main text for details. Positive and negative feedbacks are indicated by arrows with a + and a – sign, respectively. Genes and messenger ribonucleic acid … These genes, protein products, and enzymes work together to control clock functioning, and abnormalities such as clock gene mutations can have profound consequences for the synchronization of emotional, physiological, and behavioral processes with Adenylyl cyclase each other and the environment. Examples of the sometimes dramatic effects of clock gene polymorphisms in nonpsychiatric disorders are described, followed by a description of recent research on clock genes in mental disorders. Role of circadian clock genes in disorders of the sleep-wake cycle The evidence linking mutations of circadian clock genes and nonpsychlatric sleep/circadlan related disorders is compelling.