Bussi, I. | Search bioRxiv

bioRxiv2025

"Remote and partial clocks expand the circadian neuronal network, driving widespread molecular rhythmicity in Drosophila"

Circadian clocks orchestrate daily physiology and behavioral rhythms, yet the extent to which cells lacking canonical clock components exhibit robust temporal regulation remains unclear. Here we addressed this question using a two-step strategy. First, we systematically mapped core clock gene expression at single-cell resolution across the Drosophila brain and body. Second, leveraging these data and performing targeted experiments, we uncovered cells that lack most or all canonical clock components yet display strong mRNA rhythms. We found that lamina wide-field neurons show high-amplitude tim mRNA cycling even in constant darkness conditions (DD) despite minimal expression of other clock genes, suggesting a partial or noncanonical oscillator. In addition, C2 and C3 optic lobe neurons, which do not express core clock components, exhibit hundreds of circadian and daily cycling transcripts. Notably, circadian rhythms in C3 neurons coincide with oscillations of activity-regulated genes (ARGs), whereas C2 neurons cycle independently of ARGs, indicating distinct non-cell-autonomous mechanisms. These findings reveal a spectrum of circadian regulation, from autonomous to remote, input-driven rhythms and expand the circadian landscape to include strategies for generating and distributing temporal information across neuronal and non-neuronal cell types.

neuroscience↗

bioRxiv2023

Organismal landscape of clock cells and circadian gene expression in Drosophila

BackgroundCircadian rhythms time physiological and behavioral processes to 24-hour cycles. It is generally assumed that most cells contain self-sustained circadian clocks that drive circadian rhythms in gene expression that ultimately generating circadian rhythms in physiology. While those clocks supposedly act cell autonomously, current work suggests that in Drosophila some of them can be adjusted by the brain circadian pacemaker through neuropeptides, like the Pigment Dispersing Factor (PDF). Despite these findings and the ample knowledge of the molecular clockwork, it is still unknown how circadian gene expression in Drosophila is achieved across the body. ResultsHere, we used single-cell and bulk RNAseq data to identify cells within the fly that express core-clock components. Surprisingly, we found that less than a third of the cell types in the fly express core-clock genes. Moreover, we identified Lamina wild field (Lawf) and Ponx-neuro positive (Poxn) neurons as putative new circadian neurons. In addition, we found several cell types that do not express core clock components but are highly enriched for cyclically expressed mRNAs. Strikingly, these cell types express the PDF receptor (Pdfr), suggesting that PDF drives rhythmic gene expression in many cell types in flies. Other cell types express both core circadian clock components and Pdfr, suggesting that in these cells, PDF regulates the phase of rhythmic gene expression. ConclusionsTogether, our data suggest three different mechanisms generate cyclic daily gene expression in cells and tissues: canonical endogenous canonical molecular clock, PDF signaling-driven expression, or a combination of both.

molecular biology↗