Biology subjects

Spehr, M.

Publications and source records attributed to Spehr, M..

10 recordsLinked to original sources

bioRxiv2025

DNMT1 Coordinates PV Interneuron-Glia Coupling to Maintain Cortical Network Stability and Regulate Behavior

Parvalbumin (PV) interneurons are central to cortical network stability and psychiatric vulnerability. Here, we identify DNA methyltransferase 1 (DNMT1) as a key epigenetic regulator linking PV interneuron function to glial and extracellular matrix remodeling. Conditional PV-specific Dnmt1 deletion combined with single-cell RNA-seq, in vivo electrophysiology, histology, and behavioral analyses revealed that loss of DNMT1 increases PV spiking activity but reduces inhibitory efficacy, leading to network desynchronization and depression- and anxiety-like behavior in mice. These physiological alterations were accompanied by broad, non-cell-autonomous transcriptional changes in astrocytes and oligodendroglial populations, prominently affecting pathways involved in perineuronal-net (PNN) organization and neuron-glia communication. Cell-cell interaction analyses revealed disrupted NRXN-NLGN, TNR-integrin, and semaphoring signaling, consistent with weakened perisomatic adhesion and PNN integrity. Together, our findings demonstrate that DNMT1 maintains inhibitory circuit stability through cell-autonomous regulation of PV interneuron function, which secondarily shapes glial transcriptional states and extracellular scaffolds to preserve cortical network synchronization and emotional behavior.

neuroscience↗

bioRxiv2025

A cytosolic function of DNMT1 controls neuronal morphogenesis via microtubule regulation

Proteins traditionally confined to a single cellular compartment are increasingly recognized to exert non-canonical functions in alternative domains. The DNA methyltransferase 1 (DNMT1), classically defined as the maintenance methyltransferase that preserves DNA methylation patterns during replication, exemplifies this versatility. Beyond its canonical role, DNMT1 is highly expressed in the developing and adult brain, where it contributes to transcriptional regulation in postmitotic neurons. Notably, cytoplasmic DNMT1 localization has been observed in neural cells, and emerging evidence links DNMT1 to mitochondrial function with implications for neurodegenerative disease, whereby the underlying functional mechanisms remain to be fully elucidated. Here, we identify a previously unrecognized cytosolic function of DNMT1 in developing cortical excitatory neurons. Through genetic perturbation, proteomics, and high-resolution imaging, we show that DNMT1 regulates dendritic and axonal branching independently of its catalytic activity and nuclear localization. Instead, DNMT1 operates as a cytosolic scaffold interacting with the polarity regulator DOCK7 to modulate Rac1-STMN1 signaling, microtubule dynamics, and organelle trafficking. These findings expand the conceptual framework of DNMT1 from a genome guardian to a dual-compartment regulator that coordinates cytoskeletal remodeling and mitochondrial positioning. Beyond advancing our understanding of neuronal morphogenesis, this work provides mechanistic insight into how DNMT1 mutations may lead to neurodegenerative diseases.

neuroscience↗

bioRxiv2025

Insights on the effect of extracellular acidification on an HCNchannel: a molecular dynamics study

Extracellular acidification may affect the structure and function of ion channels by neutralizing acidic residues exposed to the extracellular space. However, the relationship between these changes in the protonation state and alterations in the channels structure and dynamics remains unclear. Here, we used atomistic simulations and graph-based algorithms to study mice hyperpolarization-activated cyclic nucleotide-gated type 2 channels, whose gating is facilitated by extracellular acidification. Our simulations revealed that E212, a residue facing the extracellular space, may be involved in complex hydrogen bond networks with the S4 helix, which plays a role in the gating mechanism. This network is partially disrupted at acidic pH levels, affecting the molecular interactions of the S4 helix. This, in turn, may alter the domains response to membrane voltage changes and, consequently, gating. We conclude that the H-bond network from an extracellular residue to the main gating domain may be an important factor in the observed channel activities at different pH levels. O_FIG O_LINKSMALLFIG WIDTH=157 HEIGHT=200 SRC="FIGDIR/small/674486v1_ufig1.gif" ALT="Figure 1"> View larger version (55K): org.highwire.dtl.DTLVardef@11a34c6org.highwire.dtl.DTLVardef@17ec631org.highwire.dtl.DTLVardef@5e9e4org.highwire.dtl.DTLVardef@3ea8fc_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2024

pH-dependent structural dynamics of the neuropeptide Y in aqueous solution

ABSTRACT. The neuropeptide Y regulates key molecular processes in the brain. Its interaction with the cell membrane, where it binds to specialized receptors with key physiological roles, likely depends on the pH. The structural ensembles of the porcine and human peptides, solved by Nuclear Magnetic Resonance (NMR) acid pH in aqueous solution, indicate an -helical core with unstructured termini. However, the protonation states of the carboxylic and histidine residues of the peptide, and the interplay between protonation states and peptide conformational dynamics, have not been explored. Here we perform constant pH simulations and graph-based analyses to investigate dynamics and H-bond patterns of the neuropeptide Y in the pH range from 3.0 to 7.0. We find that an -helical core, as observed in the NMR experiments, is presented at all pH values, though its length can vary by 2-3 residues depending on the pH. The pKa of Asp16, part of the -helix, and of Asp11 may shift by more than on pH unit. Based on these findings, we suggest that performing constant pH simulations may be required to describe accurately the interactions of the peptide with its cellular partners at the pH values of interest.

biophysics↗

bioRxiv2023

The rules of sex and strain: deciphering the chemical language of inbred and wild mouse conspecific scents

In most mammals, conspecific chemosensory communication relies on semiochemical release within complex bodily secretions and subsequent stimulus detection by the vomeronasal organ (VNO). Urine, a rich source of ethologically relevant chemosignals, conveys detailed information about sex, social hierarchy, health and reproductive state, which becomes accessible to a conspecific via vomeronasal sampling. So far, however, numerous aspects of social chemosignaling along the vomeronasal pathway remain unclear. Moreover, since virtually all research on vomeronasal physiology is based on secretions derived from inbred laboratory mice, it remains uncertain whether such stimuli provide a true representation of potentially more relevant cues found in the wild. Here, we combine a robust low-noise VNO activity assay with comparative molecular profiling of sex- and strain-specific mouse urine samples from two inbred laboratory strains as well as from wild mice. With comprehensive molecular portraits of these secretions, VNO activity analysis now enables us to (i) assess whether and, if so, how much sex- / strain-selective "raw" chemical information in urine is accessible via vomeronasal sampling; (ii) identify which chemicals exhibit sufficient discriminatory power to signal an animals sex, strain, or both; (iii) determine the extent to which wild mouse secretions are unique; and (iv) analyze whether vomeronasal response profiles differ between strains. We report both sex- and, in particular, strain-selective VNO representations of chemical information. Within the urinary secretome, both volatile compounds and proteins exhibit sufficient discriminative power to provide sex- and strain-specific molecular fingerprints. While total protein amount is substantially enriched in male urine, females secrete a larger variety at overall comparatively low concentrations. Surprisingly, the molecular spectrum of wild mouse urine does not dramatically exceed that of inbred strains. Finally, vomeronasal response profiles differ between C57BL/6 and BALB/c animals, with particularly disparate representations of female semiochemicals.

neuroscience↗

bioRxiv2023

Stimulus-induced theta band LFP oscillations format spiking outputs in the mouse accessory olfactory bulb

Social communication is crucial for survival of many species. In most vertebrates, a dedicated chemosensory system, the vomeronasal system (VNS), evolved to process ethologically relevant chemosensory cues. The first central VNS stage is the accessory olfactory bulb (AOB), which sends information to downstream brain regions via AOB mitral cells (AOB-MCs). Recent studies provided important insights about the functional properties of AOB-MCs, but little is known about the principles that govern their coordinated activity. Here, we recorded local field potentials (LFPs) and single unit activity in the AOB while presenting natural stimuli to adult male and female mice. Our recordings reveal prominent LFP theta band oscillatory episodes with a characteristic spatial pattern across the AOB. We find that the AOB network shows varying degrees of similarity to this pattern throughout an experiment, as a function of sensory stimulation. Analysis of LFP signal polarity and single unit activity indicate that oscillatory episodes are generated locally within the AOB, likely representing a reciprocal interaction between AOB-MCs and granule cells (GCs). Notably, spike times of many AOB-MCs are constrained to the negative LFP oscillation phase, in a manner that can drastically affect integration by downstream processing stages. Based on these observations, we propose that LFP oscillations may gate, bind, and organize outgoing signals from individual AOB neurons to downstream processing stages. Our findings suggest that, as in other neuronal systems and brain regions, population level oscillations play a key role in organizing and enhancing transmission of socially relevant chemosensory information.

neuroscience↗

bioRxiv2020

ATP activation of peritubular cells drives testicular sperm transport

Spermatogenesis, the complex developmental process of male germ cell proliferation, differentiation, and maturation, is the basis of male fertility and reproductive fitness. In the seminiferous tubules of the testes, spermatozoa are constantly generated from spermatogonial stem cells through a stereotyped sequence of mitotic and meiotic divisions. The basic physiological principles, however, that control both maturation and luminal transport of the still immotile spermatozoa within the seminiferous tubules remain poorly, if at all, defined. Here, we show that coordinated contractions of smooth muscle-like testicular peritubular cells provide the propulsive force for luminal sperm transport towards the rete testis and epididymis. Using a mouse model for in vivo imaging, we describe and quantify spontaneous tubular contractions and show a causal relationship between peritubular Ca2+ waves and peristaltic transport. Moreover, we identify P2 receptor-dependent purinergic signaling pathways as physiological triggers of tubular contractions both in vitro and in vivo. When challenged with extracellular ATP, transport of luminal content inside the seminiferous tubules displays stage-dependent directionality. We thus suggest that paracrine purinergic signaling coordinates peristaltic recurrent contractions of the mouse seminiferous tubules to propel immotile spermatozoa to the rete testis. Consequently, our findings could have substantial pharmaceutical implications for both infertility treatment and / or male contraception.

cell biology↗

bioRxiv2020

DNA methyltransferase 1 (DNMT1) function is implicated in the age-related loss of cortical interneurons

Increased life expectancy in modern society comes at the cost of age-associated disabilities and diseases. Aged brains not only show reduced excitability and plasticity, but also a decline in inhibition. Age-associated defects in inhibitory circuits likely contribute to cognitive decline and age-related disorders. Molecular mechanisms that exert epigenetic control of gene expression, contribute to age-associated neuronal impairments. Both DNA methylation, mediated by DNA methyltransferases (DNMTs), and histone modifications maintain neuronal function throughout lifespan. Here we provide evidence that DNMT1 function is implicated in the age-related loss of cortical inhibitory interneurons. Deletion of Dnmt1 in parvalbumin-positive interneurons attenuates their age-related decline in the cerebral cortex. Moreover, DNMT1-deficient mice show improved somatomotor performance and reduced aging-associated transcriptional changes. A decline in the proteostasis network, responsible for the proper degradation and removal of defective proteins, is suggested to be essentially implicated in age- and disease-related neurodegeneration. Our data suggest that DNMT1 acts indirectly on interneuron survival in aged mice by modulating the proteostasis network during life-time.

neuroscience↗

bioRxiv2018

Coordinated electrical activity in the olfactory bulb gates the oscillatory entrainment of entorhinal networks in neonatal mice

While the developmental principles of sensory and cognitive processing have been extensively investigated, their synergy has been largely neglected. During early life, most sensory systems are still largely immature. As a notable exception, the olfactory system reaches full maturity during intrauterine life, controlling mother-offspring interactions and neonatal survival. Here, we elucidate the structural and functional principles underlying the communication between olfactory bulb (OB) and lateral entorhinal cortex (LEC) - the gatekeeper of limbic circuitry - during neonatal mouse development. Combining optogenetics, pharmacology, and electrophysiology in vivo with axonal tracing, we show that mitral cell-dependent discontinuous theta bursts in OB drive network oscillations and time the firing in LEC via axonal projections confined to upper cortical layers. Pharmacological silencing of OB activity diminishes entorhinal oscillations. Moreover, odor exposure boosts OB-entorhinal coupling at fast frequencies. Thus, early OB activity shapes the maturation of entorhinal circuits.

neuroscience↗

bioRxiv2018

TRPV4 is the temperature-sensitive ion channel of human sperm

Ion channels control sperm fertilizing ability by triggering hyperactivated motility, which is regulated by membrane potential, intracellular pH, and cytosolic calcium. Previous studies unraveled three essential ion channels that regulate these parameters: 1) the Ca2+ channel CatSper, 2) the K+ channel KSper, and 3) the H+ channel Hv1. However, the molecular identity of an additional sperm Na+ conductance that mediates initial membrane depolarization and, thus, triggers downstream signaling events is yet to be defined. Here, we functionally characterize DSper, the Depolarizing Channel of Sperm, as the temperature-activated channel TRPV4. It is functionally expressed at both mRNA and protein levels, while other temperature-sensitive TRPV channels are not functional in human sperm. DSper currents are activated by warm temperatures and mediate cation conductance, that shares a pharmacological profile reminiscent of TRPV4. Together, these results suggest that TRPV4 activation triggers initial membrane depolarization, facilitating both CatSper and Hv1 gating and, consequently, sperm hyperactivation.

cell biology↗