bims-ciryme 2026-06-28 papers

Cell Mol Life Sci. 2026 Jun 25.

Divergent molecular and circuit mechanisms underlie light entrainment of retinal and suprachiasmatic nucleus circadian clocks.

A Jandot, H Calligaro, A Dianak-Shoori, K Tartour, C Sandu, N Haddjeri, C P Ribelayga, B Ananthasubramaniam, K Padmanabhan, M P Felder-Schmittbuhl, Ouria Dkhissi-Benyahya.

The circadian system aligns behavior and physiology with the 24-hour environmental cycle through a distributed network of clocks including the master pacemaker in the suprachiasmatic nucleus (SCN) and an autonomous retinal clock critical for local retinal physiology and function. Although both clocks are entrained by light, they differ in their photoreceptor inputs and light sensitivity. The specific contributions and mechanisms by which distinct photoreceptor pathways drive their photoentrainment, however, remain incompletely understood.In this study, we conducted a comprehensive transcriptomic and integrative comparative analysis of retinal and SCN circadian responses to 530 nm monochromatic light using mouse models lacking specific photoreceptors or key components of signaling pathways. Under photopic conditions, we found that each tissue displays distinct light-responsive transcriptional signatures across genotypes, yet both shared a conserved cluster of rod-driven immediate early-genes. Strikingly, the light-evoked transcriptional response was not sufficient to shift the phase of the SCN clock, in contrast to its robust phase-shifting effect on the retinal clock. Furthermore, by genetically disrupting rod/cone electrical coupling and pharmacologically isolating rod pathways, we identified the OFF-cone bipolar cell circuit as both necessary and sufficient to mediate light-induced phase resetting of the retinal clock. Together, these findings delineate the specialized retinal circuitry that supports circadian entrainment and highlight a fundamental divergence between retinal and SCN mechanisms of photic timekeeping.

Keywords: Circadian rhythm; Light; Retina; Rod; SCN

DOI: https://doi.org/10.1007/s00018-026-06298-8

FEBS J. 2026 Jun 22.

Circadian rhythms of metabolite abundance in Drosophila are largely driven by time of feeding.

Sumit Saurabh, Charlene Y P Guerrero, Madelyn R Cusick, Amanda J Samaras, Taylor M Stephenson, Sebastian L Kirkpatrick, Gregory J Matthews, Daniel J Cavanaugh.

Organisms exhibit daily oscillations in metabolite abundance. These oscillations could arise from circadian clock control of metabolic pathways or may be secondary to rhythmic food intake, which is primarily controlled by central clocks in the brain. To determine the relative contribution of central and peripheral clocks and behavioral cycles to metabolic rhythms in Drosophila, we conducted metabolite profiling with fine temporal resolution across multiple days in control flies with intact molecular clocks and in flies where CRISPR/Cas9 gene editing was used to specifically eliminate molecular circadian clock function in the fat body, a peripheral metabolic tissue, or the brain. As these latter flies lack feeding rhythms, we also included an experimental cohort of flies which lacked central brain clocks but were subjected to time-restricted feeding (TRF) protocols to impose feeding rhythms. Single-nuclei RNA sequencing confirmed selective molecular clock elimination following fat body manipulations, which was associated with predicted alterations in clock gene expression and an attenuation of time-of-day differences in the abundance of fat body transcripts involved in key metabolic pathways. Interestingly, we identified few rhythmically expressed metabolites in flies that were allowed ad libitum food access. In contrast, flies which lacked brain clocks but were raised on TRF exhibited robust circadian abundance rhythms across a large range of metabolites. These findings suggest that metabolic rhythms in Drosophila are more strongly regulated by feeding cycles than by direct circadian clock control of metabolic pathways despite the presence of metabolic genes that exhibit local clock-dependent modulation of expression across the day.

Keywords: Drosophila; circadian; metabolism; metabolomics; transcriptomics

DOI: https://doi.org/10.1111/febs.70631

NPJ Biol Timing Sleep. 2026 Jun 22. pii: 29. [Epub ahead of print]3(1):

The importance of meal timing for maintenance of daily rhythms in the gut transcriptome and microbiota.

Felicity K Hunter, Polly Downton, Andrea Luengas-Martinez, Suzanna H Dickson, Jafar Cain, Kathryn J Else, Matthew R Hepworth, Julie E Gibbs.

Gut function exhibits 24 h (circadian) rhythmicity, in part driven by intrinsic clocks within intestinal epithelial cells (IECs). The gut microbiome also demonstrates circadian rhythms in composition and function, important for maintenance of metabolic, immune and gut health. Here, we determined the influence of feeding behaviour on the 24 h colonic landscape using an interval feeding paradigm, whereby food intake was partitioned equally across the 24 h day. RNAseq analysis revealed that the IEC intrinsic clock persists in the absence of diurnal feeding rhythms; however, a subset of key transcripts loses rhythmicity, demonstrating that cell extrinsic temporal cues contribute significantly to the maintenance of the rhythmic gut transcriptome. Furthermore, interval-fed mice demonstrated a striking loss of rhythms in secretory IgA, a critical regulator of the temporal landscape of the gut microbiome. In keeping, rhythmicity within the microbiota and microbial-derived short chain fatty acids was significantly diminished. This work highlights the importance of daily rhythms in feeding behaviour for the maintenance of rhythmic processes within the gut, with implications for metabolic and immune health.

DOI: https://doi.org/10.1038/s44323-026-00089-x

Curr Opin Physiol. 2026 Mar;pii: 100875. [Epub ahead of print]47

Circadian physiology changes with aging: age is just a number, but circadian physiology keeps time.

Natalie J Bohmke, Karyn A Esser.

Circadian rhythms are inherent cycles of physiology and behavior that occur over approximately 24 h and are modulated by the cell-autonomous molecular clock. The molecular clocks throughout the body are aligned by the suprachiasmatic nucleus to contribute to robust daily variation of physiology, including core temperature, blood pressure, and heart rate. Alterations to the alignment of circadian clocks and changes to circadian rhythms of behavior and physiological processes are contributors to parameters that impact health and disease. In this review, we summarize what is known about changes to circadian rhythms of human behavior and physiology during older adulthood and the opportunities for future investigation of circadian physiology in older adults.

DOI: https://doi.org/10.1016/j.cophys.2025.100875

NPJ Biol Timing Sleep. 2026 Jun 22. pii: 24. [Epub ahead of print]3(1):

Humidity as a potential zeitgeber for circadian entrainment of insect systems.

Shyh-Chi Chen, Grace Goodhart, Daniel Eaton, Nathan Catlett, Tabitha Cady, Hannah Tran, Luke E Lutz, Lyn Wang, Ella Girard, Jaida Savino, Jodi Perry, Libby Coen, Leo Walker, Amena Bidiwala, Emma Tarter, Joshua Tompkin, Nina Greene, Aiden Yang, Joshua B Benoit.

Humidity levels, like light and temperature, fluctuate daily yet are less predictable; however, whether humidity can entrain circadian clocks and synchronize animal behaviors with environmental variations remains unknown. Here, we investigate the circadian humidity entrainment in various insects across multiple orders. Insect species respond to humidity cycles with distinct patterns, some active during either wet/dry periods or at the arid-humid transition. When the humidity cue is removed, most species continue to show rhythmic activity associated with the previous arid-humid (AH) cycles. Fruit flies shift their activity accordingly when humidity cycles are altered and remain in the new rhythms under the following free-running conditions (FRC; constant humidity, HH). Moreover, Drosophila clock and hygrosensation mutants have lower rhythmic activity during AH and a significant reduction in rhythms after humidity entrainment (FRC with HH), indicating that core clock components and hygrosensors are essential for humidity-dependent circadian entrainment. Our findings provide strong evidence that humidity is likely to serve as a potential zeitgeber for circadian entrainment in most, but not all, insect systems and should have broad applicability and importance across animal systems. While light and temperature act as the primary zeitgebers, understanding the mechanisms of humidity entrainment will help us better interpret the behavioral patterns of terrestrial animals, particularly small insects susceptible to dehydration.

DOI: https://doi.org/10.1038/s44323-026-00082-4