Biology subjects

Foster, R. G.

Publications and source records attributed to Foster, R. G..

7 recordsLinked to original sources

bioRxiv2026

Photoentrainment as Bayesian Inference: How the central circadian clock may weight and integrate the intensity and wavelength of natural light to estimate astronomical time

Synchronising with the Earth's 24-hour rotation using natural light as a timing cue presents a problem for the mammalian brain's central circadian clock. Natural light is highly variable and can take a range of values at any given time of day. For example, it fluctuates due to differences in weather conditions and across seasons. Therefore, an absolute value of light provides an uncertain indication of the time of day. Despite this uncertainty, the central clock maintains close alignment with astronomical time, and here we describe how this may be achieved computationally. We present a Bayesian model in which the clock's endogenous oscillation is used to predict the probability of observing features of light, including intensity and spectral composition, and their co-occurrence given the time of day. These predictions are drawn from a distribution of values typically experienced. When observed light falls outside the predicted range, a prediction error provides evidence that the clock may be misaligned with astronomical time. How much the clock adjusts its phase depends on the relative uncertainty associated with its internal prediction and observed light. These are combined as a weighted average according to their relative reliability, drawing the clock's updated phase towards whichever provides the more reliable estimate of astronomical time. Using natural light measurements collected over one week from 59 human observers and 100 days of environmental spectral measurements, we characterize how the variability of natural light systematically changes across the day and show how the clock may exploit this structure for circadian timekeeping. The model explains how the canonical shape of the phase response curve emerges from the relationship between light distributions and time of day, and how properties of light, including intensity and spectral composition, can be integrated according to their reliability. The central clock's synchrony to light may represent a specific instance of a general computational strategy employed by the mammalian nervous system, whereby sensory information is interpreted relative to an internally generated prediction.

neuroscience↗

bioRxiv2026

Hyperglycaemia reversibly disrupts circadian behaviour in mice

Disrupted sleep and circadian rhythms are among the most common features of diabetes, and are known to raise the risk of developing the disease. Whether the relationship also runs the other way, with diabetes itself disrupting the clock, has remained unresolved. Using an inducible mouse model of diabetes, in which hyperglycaemia can be induced and then reversed within the same animal, we show that elevated blood glucose is a reversible cause of circadian disruption. Raising blood glucose reduced the amplitude of circadian rest-activity rhythms by 50%, in proportion to the degree of hyperglycaemia, and shortened the free-running period of the clock. Restoring normoglycaemia reversed both effects. Diabetic animals had a delayed phase of activity onset, i.e. later chronotype, and re-entrained more slowly after a simulated jet lag. However, phase shifting to nocturnal light pulses was intact, suggesting normal photic responses. Brain glucose and O-GlcNAcylation, a nutrient-sensitive protein modification, were both elevated in diabetic animals, showing that peripheral hyperglycaemia reaches the brain and alters its metabolic state, and providing a molecular readout of that exposure. Together, these findings establish that a peripheral metabolic state is a reversible determinant of circadian rest-activity behaviour, completing a bidirectional link between blood glucose and the clock and arguing that the two must be treated together rather than in isolation.

neuroscience↗

bioRxiv2026

Lithium drives coordinated changes in the mouse synaptic phosphoproteome

Lithium is the gold standard mood stabiliser used to treat cycling mania and depression in bipolar disorder. Despite seven decades of clinical use, the mechanisms of its mood stabilisation are incompletely understood, fundamentally limiting development of improved alternatives. Two established lithium targets, glycogen synthase kinase 3{beta} (GSK3{beta}) and inositol monophosphatase, both modulate phosphorylation, suggesting lithium may exert broad effects on neuronal phosphorylation networks. We performed a discovery-phase in vitro screen of 140 kinases at 10mM LiCl and demonstrated that lithium inhibits 17 kinases beyond GSK3{beta}. We therefore used untargeted quantitative phosphoproteomics to create a comprehensive map of lithiums neural phosphorylation signature in lithium-treated mouse synaptoneurosomes. Samples were collected at dawn and dusk to match the peaks in phosphorylation that are induced by the sleep/wake cycle. Pathway analysis revealed convergence on synaptic plasticity, neurotransmitter release, and chemical transmission. Critically, lithium-sensitive phosphoproteins are significantly enriched in bipolar disorder genome-wide association study (GWAS) loci, providing independent genomic evidence that the phosphorylation networks we identified are relevant to bipolar pathophysiology. We identified novel kinase targets and phosphorylation sites not previously associated with lithiums mechanism of action and tied them to bipolar pathology. We further refined existing models of lithiums action by showing that GSK3{beta} inhibition is temporally restricted to dawn, indicating cross talk with sleep/wake cycles of phosphorylation. Overall, our data demonstrate that lithiums pleiotropic effects result from coordinated multi-kinase network reorganisation rather than single-target inhibition -- a principle with direct implications for rational polypharmacology in mood stabiliser development.

neuroscience↗

bioRxiv2021

Light-regulated SIK1 remodels the synaptic phosphoproteome to induce sleep

The sleep and circadian systems act in concert to regulate sleep-wake timing, yet the molecular mechanisms that underpin their interaction to induce sleep remain unknown. Synaptic protein phosphorylation, driven by the kinase SIK3, correlates with sleep pressure, however it is unclear whether these phosphoproteome changes are causally responsible for inducing sleep. Here we show that the light-dependent activity of SIK1 controls the phosphorylation of a subset of the brain phosphoproteome to induce sleep in a manner that is independent of sleep pressure. By uncoupling phosphorylation and sleep induction from sleep pressure, we establish that synaptic protein phosphorylation provides a causal mechanism for the induction of sleep under different environmental contexts. Furthermore, we propose a framework that details how the salt-inducible kinases regulate the synaptic phosphoproteome to integrate exogenous and endogenous stimuli, thereby providing the molecular basis upon which the sleep and circadian systems interact to control the sleep-wake cycle.

neuroscience↗

bioRxiv2020

Fluorescent in vivo editing reporter (FIVER): A novel multispectral reporter of in vivo genome editing

Advances in genome editing technologies have created opportunities to treat rare genetic diseases, which are often overlooked in terms of therapeutic development. Nonetheless, substantial challenges remain: namely, achieving therapeutically beneficial levels and kinds of editing in the right cell type(s). Here we describe the development of FIVER (fluorescent in vivo editing reporter) -- a modular toolkit for in vivo detection of genome editing with distinct fluorescent read-outs for non-homologous end-joining (NHEJ), homology-directed repair (HDR) and homology-independent targeted integration (HITI). We demonstrate that fluorescent outcomes reliably report genetic changes following editing with diverse genome editors in primary cells, organoids and in vivo. We show the potential of FIVER for high-throughput unbiased screens, from small molecule modulators of genome editing outcomes in primary cells through to genome-wide in vivo CRISPR cancer screens. Importantly, we demonstrate its in vivo application in postnatal organ systems of interest for genetic therapies -- retina and liver. FIVER will broadly help expedite the development of therapeutic genome surgery for many genetic disorders.

genetics↗

bioRxiv2020

The role of the hypothalamus in cortical arousaland sleep homeostasis

Sleep and wakefulness are not simple homogenous all-or-none states, but instead are characterized by rich dynamics of brain activity across many temporal and spatial scales. Rapid global state transitions between waking and sleeping are believed to be controlled by hypothalamic circuits, but the contribution of the hypothalamus to within-state changes of sleep and wake "intensity" remains largely unexplored. Here we show that stimulation of inhibitory neurons in the preoptic hypothalamus does not merely trigger awakening from sleep, but the resulting awake state is also characterized by increased cortical activity. This activation is associated with a faster build-up of sleep pressure, proportional to the arousal level. These findings show that hypothalamic systems thought to exclusively control global state switching, also regulate within-state "intensity", which we propose as a key intrinsic variable in shaping the architecture of sleep/wake states across the 24h day.

neuroscience↗

bioRxiv2020

The relationship between fasting-induced torpor,sleep and wakefulness in the laboratory mouse

Torpor is a regulated reversible state of metabolic suppression used by many mammalian species to conserve energy. Although torpor has been studied extensively in terms of general physiology, metabolism and neuroendocrinology, the effects of hypometabolism and associated hypothermia on brain activity and states of vigilance have received little attention. Here we performed continuous monitoring of electroencephalogram (EEG), electromyogram (EMG) and peripheral body temperature in adult, male C57BL/6 mice over consecutive days of scheduled restricted feeding. All animals showed prominent bouts of hypothermia that became progressively deeper and longer as fasting progressed. EEG and EMG were markedly affected by hypothermia, although the typical electrophysiological signatures of NREM sleep, REM sleep and wakefulness allowed us to perform vigilance-state classification in all cases. Invariably, hypothermia bouts were initiated from a state indistinguishable from NREM sleep, with EEG power decreasing gradually in parallel with decreasing body temperature. Furthermore, during deep hypothermia REM sleep was largely abolished, but we observed brief and intense bursts of muscle activity, which resembled the regular motor discharges seen during early ontogeny associated with immature sleep patterns. We conclude that torpor and sleep are electrophysiologically on a continuum, and that, in order for torpor to occur, mice need to first transition through euthermic sleep.

neuroscience↗