ABSTRACT
PAS (PER, ARNT, SIM) proteins play important roles in adaptation to low atmospheric and cellular oxygen levels, exposure to certain environmental pollutants, and diurnal oscillations in light and temperature. In an attempt to better understand how organisms sense environmental changes, we have characterized a novel member of the PAS superfamily, MOP9 (member of PAS superfamily), that maps to human chromosome 12p11.22-11.23. This protein displays significant homology to the Drosophila circadian factor CYCLE and its putative mammalian ortholog MOP3/bMAL1. Like its homologs, MOP9 forms a transcriptionally active heterodimer with the circadian CLOCK protein, the structurally related MOP4, and hypoxia-inducible factors, such as HIF1alpha. In a manner consistent with its role as a biologically relevant partner of these proteins, MOP9 is coexpressed in regions of the brain such as the thalamus, hypothalamus, and amygdala. Importantly, MOP9 is coexpressed with CLOCK in the suprachiasmatic nucleus, the site of the master circadian oscillator in mammals.
Subject(s)
Brain/metabolism , Drosophila Proteins , Helix-Loop-Helix Motifs , Nerve Tissue Proteins/metabolism , ARNTL Transcription Factors , Basic Helix-Loop-Helix Transcription Factors , Blotting, Northern , CLOCK Proteins , Cell Hypoxia/physiology , Cell Line , Chromosome Mapping , Circadian Rhythm/physiology , DNA-Binding Proteins/metabolism , Humans , Hypoxia-Inducible Factor 1 , Hypoxia-Inducible Factor 1, alpha Subunit , In Situ Hybridization, Fluorescence , Molecular Sequence Data , Nerve Tissue Proteins/genetics , Nerve Tissue Proteins/physiology , Nuclear Proteins/metabolism , Organ Specificity , Sequence Homology, Amino Acid , Suprachiasmatic Nucleus/metabolism , Trans-Activators/genetics , Trans-Activators/metabolism , Transcription Factors/genetics , Transcription Factors/metabolism , TransfectionABSTRACT
Circadian oscillations in mammalian physiology and behavior are regulated by an endogenous biological clock. Here we show that loss of the PAS protein MOP3 (also known as BMAL1) in mice results in immediate and complete loss of circadian rhythmicity in constant darkness. Additionally, locomotor activity in light-dark (LD) cycles is impaired and activity levels are reduced in Mop3-/- mice. Analysis of Period gene expression in the suprachiasmatic nucleus (SCN) indicates that these behavioral phenotypes arise from loss of circadian function at the molecular level. These results provide genetic evidence that MOP3 is the bona fide heterodimeric partner of mCLOCK. Furthermore, these data demonstrate that MOP3 is a nonredundant and essential component of the circadian pacemaker in mammals.
