The Box lists functional definitions of some of the terms used. Box Functional definition of some terms utilized for the description of molecular mechanisms involved in the control of gene expression. Molecular clockwork circuitry in mammals Although circadian physiology and behavior in mammals have been studied for many decades,20 the first circadian genes

(Clock, Per1, and Per2) were discovered only 10 years ago. Since then, many genes required for normal clock function have been added to the list. The approaches used in these endeavors are outlined in Table I.21-45 In analogy with early work on the Drosophila Inhibitors,research,lifescience,medical circadian oscillator these genes have been assembled into an ever more complex clockwork circuitry (Figure 1). The four transcriptional repressor-encoding genes Cry1, Cry2, Per1, and Per2 are the centerpieces

of Inhibitors,research,lifescience,medical this molecular oscillator.5 Transcription of these genes is activated via the binding of BMALlCLOCK or BMAL1-NPAS2 heterodimers to Ebox motifs of Cry and Per promoter and Inhibitors,research,lifescience,medical enhancer regions. As a consequence, Cry and Per messenger ribonucleic acid (mRNA) and protein levels rise, and once they have reached critical concentrations, CRY and PER proteins form heterotypic complexes. PER-CRY complexes directly interact with BMAL1-CLOCK or BMAL1-NPAS2 heterodimers and thereby attenuate the transactivation potential of these transcription factors.5,

28 BMAL1-CLOCK/NPAS2 heterodimers bind their target E-box sequences In a clrcadlan cycle with an opposite phase to that of CRY-PER accumulation.22 This Is compatible with a scenario In which PER-CRY complexes Inhibitors,research,lifescience,medical Impede the binding of BMAL1-CLOCK/NPAS2 heterodimers to their cognate deoxyribonucleic adlc (DNA) sequences. A secondary mechanism, Involving the orange-domain basic helix-loop-helix Inhibitors,research,lifescience,medical proteins DEC1 and DEC2 may reinforce the clrcadlan E-box binding of BMAL1-CLOCK/NPAS2 heterodimers.47 DEC1 and DEC2, both transcriptional repressors, can Selleckchem ACY 1215 establish direct proteinproteln Interactions with very BMAL1 and thereby sequester this essential clock component Into an Inactive complex. In addition, DEC proteins can compete with BMAL1-CLOCK heterodimers for E-box binding, and hence diminish E-box-dependent activation of BMAL1-CLOCK target gene expression. Although In mammals the function of DEC1 and DEC2 In circadian rhythm generation has not yet been firmly established by genetic loss-of -function experiments, this has recently been accomplished for the Drosophila ortholog clockwork orange (CWO).48-50 Post-translational mechanisms modulating the stability and/or activity of PER and CRY proteins also play pivotal roles In circadian clock function.