Biology subjects

Crosby, P.

Publications and source records attributed to Crosby, P..

8 recordsLinked to original sources

bioRxiv2026

An unrecognized host response to microbial exposure resets circadian timing

As ubiquitous features of every natural environment, microbes have profoundly shaped eukaryotic biology throughout evolution. Circadian clocks evolved in all domains of life as central regulators that align physiology with environmental cycles, yet whether they respond directly to microbial signals remains unknown. Here, we demonstrate that evolutionarily diverse microbes potently reset mammalian cellular clocks and can drive phase shifts in plants and algae, indicating cross-kingdom effects of microbes on circadian rhythms. In mammals, exposure to soluble bacterial components distinct from canonical innate immune ligands induces acute PER2 upregulation independently of Bmal1 or nascent transcription. A targeted inhibitor screen and biochemical assays implicate p38 MAPK as a modulator of this response. Taken together, this positions bacterial exposure as a previously unrecognized circadian clock input, revealing a new axis of host-microbe interaction that modulates biological timing at the cellular level.

cell biology↗

bioRxiv2025

Tandem association of CLOCK:BMAL1 complexes on DNA enables recruitment of CBP/p300 through multivalent interactions

The basic helix-loop-helix PER-ARNT-SIM (bHLH-PAS) transcription factor CLOCK:BMAL1 interacts with E-box motifs in the context of nucleosomes to elicit a circadian pattern of gene expression that oscillates with approximately 24 hour periodicity. Core clock genes and other highly rhythmic targets of CLOCK:BMAL1 typically possess a tandem arrangement of E-boxes that is required for robust oscillations. Here, we show that the presence of tandem E-boxes enables CLOCK:BMAL1 to bind more internal sites on the nucleosome, leading to release of DNA from the histone core and the presentation of multiple coactivator binding motifs in close proximity to facilitate multivalent interactions with the coactivator CBP/p300. We show that the transactivation domain (TAD) of BMAL1, essential for CLOCK:BMAL1 activity, interacts with several modular domains of CBP. Deletion of these CBP domains or chemical inhibition of protein-protein interactions with CBP significantly reduces or eliminates CLOCK:BMAL1-driven activity. Altogether, this suggests that multivalent interactions with CBP may play a role in the ability of tandem CLOCK:BMAL1 heterodimers to recruit this limiting cofactor in cells.

biophysics↗

bioRxiv2024

Potassium rhythms couple the circadian clock to the cell cycle

Circadian ([~]24 h) rhythms are a fundamental feature of life, and their disruption increases the risk of infectious diseases, metabolic disorders, and cancer1-6. Circadian rhythms couple to the cell cycle across eukaryotes7,8 but the underlying mechanism is unknown. We previously identified an evolutionarily conserved circadian oscillation in intracellular potassium concentration, [K+]i9,10. As critical events in the cell cycle are regulated by intracellular potassium11,12, an enticing hypothesis is that circadian rhythms in [K+]i form the basis of this coupling. We used a minimal model cell, the alga Ostreococcus tauri, to uncover the role of potassium in linking these two cycles. We found direct reciprocal feedback between [K+]i and circadian gene expression. Inhibition of proliferation by manipulating potassium rhythms was dependent on the phase of the circadian cycle. Furthermore, we observed a total inhibition of cell proliferation when circadian gene expression is inhibited. Strikingly, under these conditions a sudden enforced gradient of extracellular potassium was sufficient to induce a round of cell division. Finally, we provide evidence that interactions between potassium and circadian rhythms also influence proliferation in mammalian cells. These results establish circadian regulation of intracellular potassium levels as a primary factor coupling the cell- and circadian cycles across diverse organisms.

cell biology↗

bioRxiv2023

Thermosensitivity of translation underlies the mammalian nocturnal-diurnal switch

Early mammals were nocturnal until the Cretaceous-Paleogene extinction enabled diurnal niche expansion. Diurnality evolved multiple times independently, but the mechanisms driving this shift remain unclear. We identify a conserved cell-intrinsic signal inversion that facilitates the transition from nocturnality to diurnality. Diurnal and nocturnal mammalian cells respond oppositely to temperature and osmotic cycles, mirroring species activity patterns. Cells exhibit differential global responses to temperature changes, including the phosphoproteome and protein synthesis. mTOR signaling is identified as a central mediator of this inversion, with diurnal mammals converging on modifications to mTOR and WNK pathways during evolution. Reducing mTOR activity induces nocturnal-to-diurnal shifting at cellular, tissue, and organismal levels. Therefore, the mTOR pathway is a cellular nexus that integrates energetic state and environmental signals to determine activity niche.

cell biology↗

bioRxiv2022

CHRONO participates in multi-modal repression of circadian transcriptional complexes

The mammalian protein CHRONO is a rhythmically expressed repressor of the circadian transcriptional activator complex CLOCK:BMAL1, and was proposed to be a novel component of the circadian clock. However, lack of specific mechanistic understanding of the activity and function of CHRONO meant that its role within the circadian machinery was opaque. Here we fill this knowledge gap, confirming an evolutionarily conserved minimal repressive domain (MRD) of CHRONO that interacts with specific regions in the BMAL1 C-terminal transactivation domain (TAD) to repress CLOCK:BMAL1 activity. Notably, this binding region overlaps with the binding site for the repressor CRY and coactivators CBP/p300, with CHRONO capable of competing with both of these classical regulators of BMAL1 for TAD binding, highlighting CHRONO as a direct regulator of BMAL1 function. Additionally, we investigate the interaction between CHRONO and the major circadian repressor, PERIOD2 (PER2). We show that CHRONO reduces PER2 stability through interaction between the CHRONO C-terminus and the Casein Kinase 1 (CK1)-binding domain of PER2. This results in competition between CHRONO and CK1 for binding at this site on PER2, with CHRONO binding inhibiting CK1 phosphorylation of PER2 at the stabilising S662 residue. Taken together, these data show a more substantive and complex role for CHRONO in molecular circadian timekeeping than previously posited, suggesting that CHRONO acts to fine-tune cellular timekeeping by modulating multiple protein-protein interactions that are critical for maintenance of circadian rhythmicity.

biochemistry↗

bioRxiv2021

Clock gene-independent daily regulation of haemoglobin oxidation in red blood cells

Cellular circadian rhythms confer temporal organisation upon physiology that is fundamental to human health. Rhythms are present in red blood cells (RBCs), the most abundant cell type in the body, but their physiological function is poorly understood. Here, we present a novel biochemical assay for haemoglobin (Hb) oxidation status which relies on a redox-sensitive covalent haem-Hb linkage that forms during SDS-mediated cell lysis. Formation of this linkage is lowest when ferrous Hb is oxidised, in the form of ferric metHb. Daily haemoglobin oxidation rhythms are observed in RBCs cultured in vitro or taken from freely behaving mice or humans exhibit and are unaffected by mutations that affect circadian rhythms in nucleated cells. These rhythms correlate with daily rhythms in core body temperature, with temperature lowest when metHb levels are highest. Raising metHb levels with dietary sodium nitrite can further decrease daytime core body temperature in mice via NO signaling. These results extend our molecular understanding of RBC circadian rhythms and suggest they contribute to the regulation of body temperature.

cell biology↗

bioRxiv2021

Ketogenesis Impact on Liver Metabolism Revealed by Proteomics of Lysine β-hydroxybutyrylation

Ketone bodies are evolutionarily conserved metabolites that function as energy substrates, signaling molecules and epigenetic regulators. {beta}-hydroxybutyrate ({beta}-OHB) is utilized in lysine {beta}-hydroxybutyrylation (Kbhb) of histones, which associates with starvation-responsive genes, effectively coupling ketogenic metabolism with gene expression. The emerging diversity of the lysine acylation landscape prompted us to investigate the full proteomic impact of Kbhb. Global protein Kbhb is induced in a tissue-specific manner by a variety of interventions that evoke {beta}-OHB. Mass spectrometry analysis of the {beta}-hydroxybutyrylome in mouse liver revealed 891 sites of Kbhb within 267 proteins enriched for fatty acid, amino acid, detoxification and 1-carbon metabolic pathways. Kbhb of S-adenosyl-L-homocysteine hydrolase (AHCY), a rate-limiting enzyme of the methionine cycle, results in inhibition of enzymatic activity. Our results illuminate the role of Kbhb on hepatic metabolism under ketogenic conditions and demonstrate the functional consequence of this modification on a central metabolic enzyme.

molecular biology↗

bioRxiv2020

Structural mimicry confers robustness in the cyanobacterial circadian clock

The histidine kinase SasA enhances robustness of circadian rhythms in the cyanobacterium S. elongatus by temporally controlling expression of the core clock components, kaiB and kaiC. Here we show that SasA also engages directly with KaiB and KaiC proteins to regulate the period and enhance robustness of the reconstituted circadian oscillator in vitro, particularly under limiting concentrations of KaiB. In contrast to its role regulating gene expression, oscillator function does not require SasA kinase activity; rather, SasA uses structural mimicry to cooperatively recruit the rare, fold-switched conformation of KaiB to the KaiC hexamer to form the nighttime repressive complex. Cooperativity gives way to competition with increasing concentrations of SasA to define a dynamic window by which SasA directly modulates clock robustness. One Sentence SummarySasA controls the assembly of clock protein complexes through a balance of cooperative and competitive interactions.

biochemistry↗