A highland-adaptation mutation of the Epas1 protein increases its stability and disrupts the circadian clock in the plateau pika.

The Qinghai-Tibet Plateau (QTP) harbors hundreds of species well adapted to its extreme conditions, including its low-oxygen (hypoxic) atmosphere. Here, we show that the plateau pika-a keystone mammal of the QTP-lacks robust circadian rhythms. The major form of the plateau pika Epas1 protein includes a 24-residue insert caused by a point mutation at the 5' juncture site of Intron14 and is more stable than other mammalian orthologs. Biochemical studies reveal that an Epas1-Bmal1 complex with lower trans-activation activity occupies the E1/E2 motifs at the promoter of the core-clock gene Per2, thus explaining how an Epas1 mutation-selected in the hypoxic conditions of the QTP-disrupts the molecular clockwork. Importantly, experiments with hypoxic chambers show that mice expressing the plateau pika Epas1 ortholog in their suprachiasmatic nucleus have dysregulated central clocks, and pika Epas1 knockin mice reared in hypoxic conditions exhibit dramatically reduced heart damage compared with wild-type animals.

Chemical perturbations reveal that RUVBL2 regulates the circadian phase in mammals.

Transcriptional regulation lies at the core of the circadian clockwork, but how the clock-related transcription machinery controls the circadian phase is not understood. Here, we show both in human cells and in mice that RuvB-like ATPase 2 (RUVBL2) interacts with other known clock proteins on chromatin to regulate the circadian phase. Pharmacological perturbation of RUVBL2 with the adenosine analog compound cordycepin resulted in a rapid-onset 12-hour clock phase-shift phenotype at human cell, mouse tissue, and whole-animal live imaging levels. Using simple peripheral injection treatment, we found that cordycepin penetrated the blood-brain barrier and caused rapid entrainment of the circadian phase, facilitating reduced duration of recovery in a mouse jet-lag model. We solved a crystal structure for human RUVBL2 in complex with a physiological metabolite of cordycepin, and biochemical assays showed that cordycepin treatment caused disassembly of an interaction between RUVBL2 and the core clock component BMAL1. Moreover, we showed with spike-in ChIP-seq analysis and binding assays that cordycepin treatment caused disassembly of the circadian super-complex, which normally resides at E-box chromatin loci such as PER1, PER2, DBP, and NR1D1 Mathematical modeling supported that the observed type 0 phase shifts resulted from derepression of E-box clock gene transcription.