bims-ciryme 2026-02-08 papers

Proc Natl Acad Sci U S A. 2026 Feb 10. 123(6): e2525126123

A daily cycle of White Collar Complex dephosphorylation sustains circadian rhythmicity in Neurospora.

Bin Wang, Xiaoying Zhou, Jennifer J Loros, Jay C Dunlap.

The transcription factor complex White Collar Complex (WCC) functions both as a photoreceptor and as the circadian positive element. In response to light, WCC acutely activates ~5% of all genes, whereas in the dark it influences expression of about 40% of the transcriptome. Among WCC targets is frq, which is acutely light-activated through the pLRE (proximal Light-Response Element) and circadian-regulated through the C-box (Clock-box) promoter element that is not responsible for light-driven expression. The FRQ-FRH complex (FFC), which includes CK-1a, represses WCC activity at the C-box by phosphorylating WCC at >95 sites, but FFC has no described role in the light. We validated the expectation that FFC also silences C-box promoters in constant light, thereby confirming two classes of WCC targets: C-box-like genes that are normally repressed in light and pLRE-like genes that remain light-active despite FFC-driven WCC phosphorylation. Derepression of C-box-like promoters in frq-null fungi may explain reported noncircadian phenotypes such as reduced virulence and conidiation. Reanalysis of WCC circadian regulation revealed that, while most WCC is phosphorylated and repressed at dusk, subsequent circadian activation results from transient dephosphorylation of only a small subset of the WCC pool. This small active pool drives frq expression, nucleating the FFC, which rephosphorylates WCC to repress it again, generating a phosphorylation/dephosphorylation cycle that can persist for days without new WCC synthesis. The realization that both FFC and WCC are regulated primarily through phosphorylation rather than protein turnover leaves the circadian oscillator looking much like a "phoscillator," emphasizing the primacy of posttranslational regulation in timekeeping.

Keywords: FFC; WC-1; WC-2; WCC activity; dephosphorylation

DOI: https://doi.org/10.1073/pnas.2525126123

Proc Natl Acad Sci U S A. 2026 Feb 03. 123(5): e2511093123

REV-ERB-alpha and -beta coordinately regulate astrocyte reactivity and proteostatic function.

Collin J Nadarajah, Michelle Y Li, Elsa I Quillin, Kevin Boyer, Julie M Dimitry, Yining Chen, Melvin W King, Ibrahim O Saliu, Jiyeon Lee, Patrick W Sheehan, Albert A Davis, Mitchell A Lazar, Guoyan Zhao, Erik S Musiek.

The molecular circadian clock is a ubiquitous transcriptional-translational feedback loop that regulates CNS function, glial responses, and neurodegenerative pathology. The nuclear receptors REV-ERB-α (Nr1d1) and REV-ERB-β (Nr1d2) are components of the core circadian clock which regulate metabolism, neuroinflammatory responses, synaptic pruning, and protein aggregation, though the cell type-specific effects and relative compensatory effects of REV-ERB-α AND -β in the brain are unknown. To study the CNS functions of REV-ERBs, we developed mouse lines with global or astrocyte-specific, conditional knockout of both REV-ERB-α and -β. We demonstrate that inducible postnatal global deletion of both REV-ERB-α and -β unmasks extensive transcriptional changes in the brain in disease-relevant pathways such as protein catabolism, complement, and oxidative stress which are not observed with REV-ERB-α deletion alone, and drives spontaneous astrocyte reactivity. Astrocyte-specific deletion of REV-ERB-α/-β recapitulates this spontaneous astrocyte reactivity phenotype, indicating that REV-ERBs regulate astrocyte activation in a cell-autonomous manner downstream of the core circadian clock. Upstream transcription factor analysis revealed that REV-ERB-α/-β repress transcription of Stat3, and astrocytic deletion of REV-ERBs induced astrocytic STAT3 expression and downstream STAT3-mediated gene expression, providing a mechanistic link to the astrocyte reactivity shift. Dual REV-ERB deletion enhanced astrocyte alpha-synuclein uptake and protein degradation in vitro and mitigated alpha-synuclein spreading pathology in an in vivo model of Parkinson's Disease. This study reveals REV-ERBs as regulators of astrocyte function and implicates astrocyte REV-ERBs as potential therapeutic targets to prevent synucleinopathies and other neurodegenerative pathologies.

Keywords: REV-ERBalpha; alpha-synuclein; astrocyte; circadian; neuroinflammation

DOI: https://doi.org/10.1073/pnas.2511093123

bioRxiv. 2026 Jan 12. pii: 2026.01.12.699091. [Epub ahead of print]

Rhythmic Nuclear Import Mediated by Importins Regulates the Neurospora Circadian Clock.

Ziyan Wang, Bin Wang, Bradley M Bartholomai, Jennifer J Loros, Jay C Dunlap.

Circadian clocks in eukaryotes rely on precisely regulated negative feedback loops to generate daily rhythms. However, the delay mechanisms that extend this structurally simple feedback loop to ∼24 hours are not yet fully understood. In the filamentous fungal model organism Neurospora crassa , the negative arm complex, centered by FREQUENCY (FRQ), must enter the nucleus to repress the White Collar Complex (WCC) and close the feedback loop, but the mechanisms and dynamics of its nuclear transport have remained unresolved. Using long-term live-cell imaging and fluorescence recovery after photobleaching (FRAP), we demonstrate that FRQ nuclear import is an active circadian-regulated process that is fastest early in the subjective day and progressively decreases as nuclear FRQ approaches peak levels, corresponding to altered direct binding between FRQ and Importin α. We further establish that Importin α is required for the spatial regulation of FRQ and WC-1 and the correct timing of Neurospora circadian clock. Analysis of the three Neurospora Importin β homologs reveals that each of them contributes differently to the circadian clock through pathways beyond FRQ or WCC nuclear import. More specifically, we find a genetic interaction between Impβ3 and the phosphatase PP-4. Together, these findings indicate that nuclear import is a selective, dynamic, and rate-limiting regulatory step in the fungal circadian clock and reveal both conserved and fungal-specific mechanisms by which importins tune circadian timing.

DOI: https://doi.org/10.64898/2026.01.12.699091

Nat Metab. 2026 Feb 05.

Feeding-regulated glycogen metabolism drives rhythmic liver protein secretion.

The liver has a key role in inter-organ communication by secreting most circulating plasma proteins. However, the mechanisms governing hepatic protein secretion remain unclear. Here we show that hepatic protein secretion follows a diurnal rhythm regulated by food intake in humans and mice. Using liver microsomal proteomics, we find that proteins implicated in the early secretory pathway, such as protein glycosylation and folding in the endoplasmic reticulum (ER) and Golgi apparatus, exhibit a rhythmic expression profile, which is abolished in Bmal1-knockout mice. Mechanistically, we show that hepatic glycogenolysis provides substrates for protein N-glycosylation. In mice, perturbing hepatic glycogenolysis with pharmacological or nutritional interventions leads to ER stress and attenuates diurnal protein secretion. We confirm these results in humans, as genetic variants associated with glycogen storage disease and congenital disorders of glycosylation also alter hepatic protein secretion. Overall, our work uncovers hepatic glycogen metabolism as a circadian regulator of protein secretion.

DOI: https://doi.org/10.1038/s42255-026-01453-8

Proc Natl Acad Sci U S A. 2026 Feb 10. 123(6): e2521268123

Neurotensin in the extended amygdala maintains wakefulness in novel environments.

Chi Jung Hung, Shuhei Ueda, Sheikh Mizanur Rahaman, Mikiyasu Yamamoto, Jiahui Li, Noriaki Fukatsu, Haruhiko Bito, Hiroshi Yamaguchi, Akihiro Yamanaka, Sayaka Takemoto-Kimura, Daisuke Ono.

Animals remain awake in unfamiliar environments to assess potential safety threats, a process involving changes in neuronal activity within sleep-wake regulatory brain regions. However, the specific circuits and neurotransmitters involved remain poorly understood. Here, we show that neurotensin (NTS) peptides in corticotropin-releasing factor (CRF) neurons of the lateral part of the interstitial nucleus of the posterior limb of the anterior commissure (IPACL) play a key role in maintaining wakefulness in response to environmental changes. Activation of IPACLCRF neurons increased wakefulness, whereas their inhibition or deletion of NTS reduced wakefulness in novel environments. These neurons are activated in response to exposure to a novel environment and project primarily to the substantia nigra pars reticulata (SNr) and release NTS, which modulates wakefulness. These findings suggest that NTS signaling from IPACLCRF neurons to the SNr is essential for sustaining wakefulness in unfamiliar or changing environments.

Keywords: interstitial nucleus of the posterior limb of the anterior commissure; neurotensin; novel environments; substantia nigra; wakefulness

DOI: https://doi.org/10.1073/pnas.2521268123