A High-Throughput Live Imaging Platform to Investigate Circuit-Dependent Regulation of Circadian Rhythms in Brain...

Circadian function in multicellular organisms arises from coordinated interactions amongst diverse cellular tissue populations. Existing approaches for long-term imaging of within-tissue circadian regulation remain low-throughput, highly specialized, and largely inaccessible. Here, we developed ClockCyte, a high-content fluorescent live-imaging platform that enables continuous monitoring of circadian rhythms in up to 144 brain tissue samples. Using the mouse suprachiasmatic nucleus as a model, ClockCyte captures the differential circadian tissue regulation of neurons and astrocytes. We further identified a previously uncharacterized oscillatory circadian compartment in axonal calcium, showing highly homogeneous activity, opposed to waves of intracellular neuronal calcium. By deleting Bmal1 in neurons, we reveal the network underpinnings connecting clock gene expression to network-wide axonal regulation. The discovery of distinct circadian properties of axonal calcium and their disruption by Bmal1 ablation highlights the potential to reveal new principles of intra-tissue network-level circadian organization. More broadly, this approach will enable systematic explorations of how cell-type-specific and compartmentalized subcellular rhythms contribute to brain physiology.