Biology subjects

Herzog, E. D.

Publications and source records attributed to Herzog, E. D..

9 recordsLinked to original sources

bioRxiv2024

The Functional Connectome Mediating Circadian Synchrony in the Suprachiasmatic Nucleus

Circadian rhythms in mammals arise from the spatiotemporal synchronization of [~]20,000 neuronal clocks in the Suprachiasmatic Nucleus (SCN). While anatomical, molecular, and genetic approaches have revealed diverse cell types and signaling mechanisms, the network wiring that enables SCN cells to communicate and synchronize remains unclear. To overcome the challenges of revealing functional connectivity from fixed tissue, we developed MITE (Mutual Information & Transfer Entropy), an information theory approach that infers directed cell-cell connections with high fidelity. By analyzing 3447 hours of continuously recorded clock gene expression from 9011 cells in 17 mice, we found that the functional connectome of SCN was highly conserved bilaterally and across mice, sparse, and organized into a dorsomedial and a ventrolateral module. While most connections were local, we discovered long-range connections from ventral cells to cells in both the ventral and dorsal SCN. Based on their functional connectivity, SCN cells can be characterized as circadian signal generators, broadcasters, sinks, or bridges. For example, a subset of VIP neurons acts as hubs that generate circadian signals critical to synchronize daily rhythms across the SCN neural network. Simulations of the experimentally inferred SCN networks recapitulated the stereotypical dorsal-to-ventral wave of daily PER2 expression and ability to spontaneously synchronize, revealing that SCN emergent dynamics are sculpted by cell-cell connectivity. We conclude that MITE provides a powerful method to infer functional connectomes, and that the conserved architecture of cell-cell connections mediates circadian synchrony across space and time in the mammalian SCN. HighlightsO_LIWe developed MITE, an information theory method, to accurately infer directed functional connectivity among circadian cells. C_LIO_LISCN cell types with conserved connectivity patterns spatially organize into two regions and function as generators, broadcasters, sinks, or bridges of circadian information. C_LIO_LIOne-third of VIP neurons serve as hubs that drive circadian synchrony across the SCN. C_LIO_LIKey connectivity features mediate the generation and maintenance of intercellular synchrony and daily waves of clock gene expression across the SCN. C_LI

neuroscience↗

bioRxiv2024

Daily glucocorticoids promote glioblastoma growth and circadian synchrony to the host

Glioblastoma (GBM) is the most common primary brain tumor in adults with a poor prognosis despite aggressive therapy. A recent, retrospective clinical study found that administering Temozolomide in the morning increased patient overall survival by 6 months compared to evening. Here, we tested the hypothesis that daily host signaling regulates tumor growth and synchronizes circadian rhythms in GBM. We found daily Dexamethasone promoted or suppressed GBM growth depending on time of day of administration and on the clock gene, Bmal1. Blocking circadian signals, like VIP or glucocorticoids, dramatically slowed GBM growth and disease progression. Finally, mouse and human GBM models have intrinsic circadian rhythms in clock gene expression in vitro and in vivo that entrain to the host through glucocorticoid signaling, regardless of tumor type or host immune status. We conclude that GBM entrains to the circadian circuit of the brain, which modulates its growth through clock-controlled cues, like glucocorticoids.

neuroscience↗

bioRxiv2023

Circadian regulation of MGMT expression and promoter methylation underlies daily rhythms in TMZ sensitivity in glioblastoma

BackgroundGlioblastoma (GBM) is the most common primary brain tumor in adults. Despite extensive research and clinical trials, median survival post-treatment remains at 15 months. Thus, all opportunities to optimize current treatments and improve patient outcomes should be considered. A recent retrospective clinical study found that taking TMZ in the morning compared to the evening was associated with a 6-month increase in median survival in patients with MGMT-methylated GBM. Here, we hypothesized that TMZ efficacy depends on time-of-day and O6-Methylguanine-DNA Methyltransferase (MGMT) activity in murine and human models of GBM. Methods and ResultsIn vitro recordings using real-time bioluminescence reporters revealed that GBM cells have intrinsic circadian rhythms in the expression of the core circadian clock genes Bmal1 and Per2, as well as in the DNA repair enzyme, MGMT. Independent measures of MGMT transcript levels and promoter methylation also showed daily rhythms intrinsic to GBM cells. These cells were more susceptible to TMZ when delivered at the daily peak of Bmal1 transcription. We found that in vivo morning administration of TMZ also decreased tumor size and increased body weight compared to evening drug delivery in mice bearing GBM xenografts. Finally, inhibition of MGMT activity with O6-Benzylguanine abrogated the daily rhythm in sensitivity to TMZ in vitro by increasing sensitivity at both the peak and trough of Bmal1 expression. ConclusionWe conclude that chemotherapy with TMZ can be dramatically enhanced by delivering at the daily maximum of tumor Bmal1 expression and minimum of MGMT activity. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=164 SRC="FIGDIR/small/557630v1_ufig1.gif" ALT="Figure 1"> View larger version (36K): org.highwire.dtl.DTLVardef@2e9058org.highwire.dtl.DTLVardef@1069917org.highwire.dtl.DTLVardef@2cf000org.highwire.dtl.DTLVardef@40abc9_HPS_FORMAT_FIGEXP M_FIG C_FIG

cancer biology↗

bioRxiv2023

Fetal daily rhythms develop during pregnancy and entrain to the maternal circadian system

Circadian rhythms in gene expression and hormones are ubiquitous across species and differentiated cell types. This study aimed to determine when daily rhythms begin in the fetus and synchronize to the mother. We developed methods to monitor the expression of fetal PERIOD2 (PER2), a core circadian clock protein, in mice longitudinally from embryonic day (E)8.5 to E17.5 through in utero bioluminescence imaging. We found that embryonic PER2 expression increased rapidly throughout pregnancy and exhibited day-night rhythms from the start of our recordings at E8.5. The daily peak time of PER2 varied between pregnancies until it reliably peaked at night and synchronized to the mother starting around E15.5. Loss of fetal circadian rhythms associated with pregnancies that ultimately failed. Because maternal glucocorticoids have been implicated in fetal development and synchronizing circadian tissues, we tested their sufficiency to shift fetal daily rhythms in utero. Daily glucocorticoids injections over five days of late pregnancy advanced fetal PER2 rhythms in utero and blocking glucocorticoid signaling in vitro reduced PER2 synchrony between the maternal and fetal placenta by [~]40%. We conclude that fetal daily rhythms arise early in pregnancy and then synchronize with the maternal rhythm prior to birth depending, in part, on glucocorticoid signaling.

developmental biology↗

bioRxiv2022

Circadian rhythms in multiple behaviors depend on sex, neuropeptide signaling, and ambient light

Organisms have evolved circadian (near-24 h) rhythms in behavior to anticipate daily opportunities and challenges such as mating and predation. However, the ethological investigation of circadian behavioral rhythms has been traditionally limited to studying easy-to-measure behaviors at higher temporal resolution or difficult-to-measure behaviors with limited temporal resolution. Our ability to simultaneously record circadian rhythms in multiple behaviors has also been limited by currently available technology. We thus sought to examine eight overt, ethologically-relevant behaviors never before studied simultaneously as a function of time of day: eating, drinking, grooming, rearing, nesting, digging, exploring, and resting. To address the hypothesis that the daily patterning of these behaviors depends on neuropeptide signaling, sex, and ambient light, we used high-throughput machine learning to automatically score millions of video frames of freely-behaving male and female wild-type and vasoactive intestinal peptide (Vip)-deficient mice. Automated frame-by-frame predictions of the eight behaviors correlated highly with consensus labels by trained human classifiers. We discovered reliable daily rhythms in many previously unreported behaviors that peaked at stereotyped times of day and persisted in constant darkness. Surprisingly, nesting and digging rhythms differed dramatically in both phase and amplitude between male and female mice. In Vip-deficient mice, daily rhythms in most behaviors were low amplitude and peaked earlier in the day in a light:dark cycle, while rhythms in all behaviors peaked randomly throughout the day in constant darkness. We also found that for most behaviors, time budgets predominantly differed by light cycle, but transition probabilities predominantly differed with VIP signaling and by sex. We conclude that machine learning can be used to reveal novel sex, neuropeptide, and light-dependent behaviors at time scales from seconds to days.

animal behavior and cognition↗

bioRxiv2020

Adult mice lacking VIP SCN neurons retain circadian locomotor behavior but exhibit dampened daily glucocorticoid rhythms

The suprachiasmatic nucleus (SCN) drives circadian rhythms in locomotion through coupled, single-cell oscillations. Global genetic deletion of the neuropeptide, Vip or its receptor Vipr2, results in profound deficits in daily synchrony among SCN cells and daily rhythms in locomotor behavior and glucocorticoid secretion. To test whether this phenotype depends on VIP neurons in the SCN, we ablated VIP SCN neurons in vivo in adult mice through Caspase3-mediated induction of the apoptotic pathway in cre-expressing VIP neurons. We found that ablation of VIP SCN neurons in adult mice caused a phenotype distinct from Vip- and Vipr2- null mice. Mice lacking VIP neurons retained rhythmic locomotor activity with a shortened circadian period, more variable onsets and decreased duration of daily activity. Circadian hormonal outputs, specifically corticosterone rhythms were severely dampened. In contrast, deletion of neonatal SCN VIP neurons dramatically reduced circadian gene expression in the cultured SCN, mimicking the effects of global deletion of Vip or Vipr2. These results suggest that SCN VIP neurons play a role in lengthening circadian period and stimulating the daily surge in glucocorticoids in adults and in synchronizing and sustaining daily rhythms among cells in the developing SCN. Significance StatementThe importance of the neuropeptide, VIP, for circadian rhythms has been described in mice lacking the gene for Vip or its receptor, Vipr2. This study found that ablation of VIP neurons only in the adult SCN reproduced the loss of circadian rhythms in glucocorticoids, but not the loss of circadian locomotor behavior, seen with global loss of VIP signaling. We conclude that VIP SCN neurons play two roles: one in adulthood lengthening circadian period and regulating circadian outputs, and one in development coordinating synchrony among circadian cells.

neuroscience↗

bioRxiv2018

Entrainment of circadian rhythms depends on firing rates and neuropeptide release of VIP SCN neurons

The mammalian suprachiasmatic nucleus (SCN) functions as a master circadian pacemaker, integrating environmental input to align physiological and behavioral rhythms to local time cues. Approximately 10% of SCN neurons express vasoactive intestinal polypeptide (VIP); however, it is unknown how firing activity of VIP neurons releases VIP to entrain circadian rhythms. To identify physiologically relevant firing patterns, we optically tagged VIP neurons and characterized spontaneous firing over three days. VIP neurons had circadian rhythms in firing rate and exhibited two classes of instantaneous firing activity. We next tested whether physiologically relevant firing affected circadian rhythms through VIP release. We found that VIP neuron stimulation with high, but not low, frequencies shifted gene expression rhythms in vitro through VIP signaling. In vivo, high frequency VIP neuron activation rapidly entrained circadian locomotor rhythms. Thus, increases in VIP neuronal firing frequency release VIP and entrain molecular and behavioral circadian rhythms.\n\nHighlightsO_LIMazuski et al. identified three classes of circadian SCN neurons based on their distinct firing patterns consistent over multiple days\nC_LIO_LIThere are two distinct classes (tonic and irregular firing) of VIP SCN neurons.\nC_LIO_LIStimulation of VIP SCN neurons at physiologically relevant frequencies phase shifts whole-SCN circadian rhythms in gene expression through VIP release. These effects are blocked with VIP antagonists.\nC_LIO_LIFiring of VIP SCN neurons entrains circadian rhythms in locomotor behavior in a frequency and time-of-day dependent manner.\nC_LI

neuroscience↗

bioRxiv2018

Circadian clock neurons mediate time-of-day dependent responses to light

Circadian (~24 h) rhythms influence nearly all aspects of physiology, including sleep/wake, metabolism, and hormone release. The suprachiasmatic nucleus (SCN) synchronizes these daily rhythms to the external light cycle, but the mechanisms by which this occurs is unclear. The neuropeptide vasoactive intestinal peptide (VIP) is the predominant contributor to synchrony within the SCN and is important for circadian light responses, but the role of VIP neurons themselves is unclear. Thus, we tested the hypothesis that rhythmic SCN VIP neurons mediate circadian light responses. Using in vivo fiber photometry recording of SCN VIP neurons we found daily rhythms in spontaneous calcium events that peaked during the subjective day and in light-evoked calcium events that exhibited the greatest response around subjective dusk. These rhythms were correlated with spontaneous and NMDA-evoked VIP release from SCN VIP neurons in vitro. Finally, in vivo hyperpolarization of VIP neurons attenuated light-induced shifts of daily rhythms in locomotion. We conclude that SCN VIP neurons are circadian and depolarize to light to modulate entrainment of daily rhythms in the SCN and behavior.

neuroscience↗

bioRxiv2017

Neuronal tracing and analysis by multispectral tracing in densely labeled mouse brain

Accurate and complete neuronal wiring diagrams are necessary for understanding brain function at many scales from long-range interregional projections to microcircuits. Traditionally, light microscopy-based anatomical reconstructions use monochromatic labeling and therefore necessitate sparse labeling to eliminate tracing ambiguity between intermingled neurons. Consequently, our knowledge of neuronal morphology has largely been based on averaged estimations across many samples. Recently developed second-generation Brainbow tools promise to circumvent this limitation by revealing fine anatomical details of many unambiguously identifiable neurons in densely labeled samples. Yet, a means to quantify and analyze the information is currently lacking. Therefore, we developed nTracer, an ImageJ plugin capable of rapidly and accurately reconstructing whole-cell morphology of large neuronal populations in densely labeled brains.

neuroscience↗