Biology subjects

Francis, N.

Publications and source records attributed to Francis, N..

10 recordsLinked to original sources

bioRxiv2026

Mice detect and discriminate temporal patterns of mesoscale optogenetic cortical stimulation

Optogenetic stimulation is widely used to establish causal links between neural activity, behavior, and sensory perception, yet animals may also perceive the neural stimulation itself, a phenomenon termed "optoception." We hypothesized that cortical optogenetic stimulation would generate an artificial percept that could be distinguished from externally evoked sensations and characterized psychometrically in an operant task. We tested this hypothesis using mesoscale cortical photostimulation delivered by a 3 mm, 459 nm LED implanted over auditory cortex. Four mice expressing Channelrhodopsin-2 (ChR2) in excitatory neurons learned a head-fixed go/no-go task in which 20 Hz cortical photostimulation served as the target. ChR2-positive mice detected cortical photostimulation relative to LED-off catch trials, distinguished it from both an external LED matched in wavelength and pulse rate and from an acoustic noise matched in amplitude-modulation rate, and discriminated between 20- and 10-Hz cortical photostimulation. Reducing implanted-LED optical power initially lowered rate-discrimination sensitivity, which then increased across training sessions, demonstrating perceptual learning. In two mice tested with 11 randomly interleaved rates spanning 10-20 Hz, lick probability followed a saturating rate-dependent function. Two ChR2-negative littermates failed to acquire photostimulation-locked behavioral responding. Together, these findings show that mesoscale cortical optogenetic stimulation generates a graded, learnable artificial percept whose behavioral readout depends on photostimulation rate and optical power. This single-LED preparation provides a cost-efficient and wavelength-extensible platform for psychometric analysis of optoception.

neuroscience↗

bioRxiv2024

Vocal Call Locator Benchmark (VCL) for localizing rodent vocalizations from multi-channel audio

Understanding the behavioral and neural dynamics of social interactions is a goal of contemporary neuroscience. Many machine learning methods have emerged in recent years to make sense of complex video and neurophysiological data that result from these experiments. Less focus has been placed on understanding how animals process acoustic information, including social vocalizations. A critical step to bridge this gap is determining the senders and receivers of acoustic information in social interactions. While sound source localization (SSL) is a classic problem in signal processing, existing approaches are limited in their ability to localize animal-generated sounds in standard laboratory environments. Advances in deep learning methods for SSL are likely to help address these limitations, however there are currently no publicly available models, datasets, or benchmarks to systematically evaluate SSL algorithms in the domain of bioacoustics. Here, we present the VCL Benchmark: the first large-scale dataset for benchmarking SSL algorithms in rodents. We acquired synchronized video and multi-channel audio recordings of 767,295 sounds with annotated ground truth sources across 9 conditions. The dataset provides benchmarks which evaluate SSL performance on real data, simulated acoustic data, and a mixture of real and simulated data. We intend for this benchmark to facilitate knowledge transfer between the neuroscience and acoustic machine learning communities, which have had limited overlap.

neuroscience↗

bioRxiv2024

Unbiased multiplex antigen screening of Cerebrospinal Fluid detects microbial and autoantigenic epitopes associated with Multiple Sclerosis

To comprehensively investigate the intrathecal antibody profile of multiple sclerosis (MS), we examined the cerebrospinal fluid of 195 patients (92 MS and 103 non-MS) for antibodies using a multiplex unbiased bacteria peptide library. We first tested against Epstein-Barr nuclear antigen 1 (EBNA1) for epitope sites enriched in MS and found a significant enrichment at position 407-419. We then used the data to perform a high-throughput screen against a library of 129 viruses known to infect humans. We discovered several additional epitopes from viruses such as Hantaan virus, Human Herpesvirus 6A and Human respiratory syncytial virus B associated with MS. Besides viral epitopes, we also screened for potential autoantigens of the central nervous system (CNS). We discovered several autoantigenic epitopes in proteins such as ADRB3, HTR3A and MPO that were significantly enriched for MS. Because of previous associations of Toxoplasma gondii infection with MS, we also performed a Toxoplasma gondii specific analysis and discovered additional epitopes enriched for MS. We further assessed epitope-epitope correlations within the patient samples and found distinct patterns of association between these microbial and autoantigenic epitopes. Finally, we performed machine-learning to determine if these epitopes are predictive for MS and found that the model incorporating all the epitopes could most effectively discriminate between MS and non-MS (ROC-AUC score = 0.91). Our results demonstrate the effectiveness of multiplex unbiased screens to detect the identity of potentially cross-reactive antibodies targeting MS CNS epitopes and they can also be used as effective biomarkers for MS. One Sentence SummaryWe performed an unbiased multiplex bacteria peptide antibody library screen on cerebrospinal fluid samples of patients with multiple sclerosis (MS) as well as non-MS controls and detected multiple viral and autoantigenic epitopes that are significantly enriched in MS patient samples.

immunology↗

bioRxiv2023

How a disordered linker in the Polycomb protein Polyhomeotic tunes phase separation and oligomerization

Biomolecular condensates are increasingly appreciated for their function in organizing and regulating biochemical processes in cells, including chromatin function. Condensate formation and properties are encoded in protein sequence but the mechanisms linking sequence to macroscale properties are incompletely understood. Cross species comparisons can reveal mechanisms either because they identify conserved functions or because they point to important differences. Here we use in vitro reconstitution and molecular dynamics simulations to compare Drosophila and human sequences that regulate condensate formation driven by the sterile alpha motif (SAM) oligomerization domain in the Polyhomeotic (Ph) subunit of the chromatin regulatory complex PRC1. We discover evolutionarily diverged contacts between the conserved SAM and the disordered linker that connects it to the rest of Ph. Linker-SAM interactions increase oligomerization and regulate formation and properties of reconstituted condensates. Oligomerization affects condensate dynamics but, in most cases, has little effect on their formation. Linker-SAM interactions also affect condensate formation in Drosophila and human cells, and growth in Drosophila imaginal discs. Our data show how evolutionary sequence changes in linkers connecting conserved structured domains can alter condensate properties. In briefLinking sequence to macroscale properties of biomolecular condensates remains elusive. The authors dissect the function of a disordered linker connecting conserved structured domains in a Polycomb protein with biochemistry and molecular dynamics simulations revealing how sequence changes between Drosophila and humans alter condensates and growth in cells and developing flies. O_FIG O_LINKSMALLFIG WIDTH=168 HEIGHT=200 SRC="FIGDIR/small/564264v2_ufig1.gif" ALT="Figure 1"> View larger version (40K): org.highwire.dtl.DTLVardef@a8bd84org.highwire.dtl.DTLVardef@322eaeorg.highwire.dtl.DTLVardef@96a3a8org.highwire.dtl.DTLVardef@1d2a978_HPS_FORMAT_FIGEXP M_FIG Graphical abstract C_FIG HighlightsO_LIPRC1 condensates form partly through the conserved SAM domain of Polyhomeotic (Ph) C_LIO_LILinker connecting Ph domains regulates SAM oligomerization and phase separation C_LIO_LILinker-SAM contacts with human but not fly linker in molecular dynamics simulations C_LIO_LILinker-SAM contacts tune condensates in vitro and in cells, and affect cell growth C_LI

biochemistry↗

bioRxiv2022

Adaptation to ex vivo culture drives human haematopoietic stem cell loss of repopulation capacity in a cell cycle independent manner

Loss of long-term haematopoietic stem cell function (LT-HSC) hampers the success of ex vivo HSC gene therapy and expansion procedures, but the kinetics and the mechanisms by which this occurs remain incompletely characterized. Here through time-resolved scRNA-Seq, matched in vivo functional analysis and the use of a reversible in vitro system of early G1 arrest, we define the sequence of transcriptional and functional events occurring during the first ex vivo division of human LT-HSCs. We demonstrate that contrary to current assumptions, loss of long-term repopulation capacity during culture is independent of cell cycle progression. Instead it is a rapid event that follows an early period of adaptation to culture, characterised by transient gene expression dynamics and constrained global variability in gene expression. Cell cycle progression however contributes to the establishment of differentiation programmes in culture. Our data have important implications for improving HSC gene therapy and expansion protocols.

cell biology↗

bioRxiv2021

Sequential Transmission of Task-Relevant Information in Cortical Neuronal Networks

During auditory task performance, cortical processing of task-relevant information enables mammals to recognize sensory input and flexibly select behavioral responses. In mouse auditory cortex, small neuronal networks encode behavioral choice during a pure-tone detection task, but it is poorly understood how neuronal networks encode behavioral choice during a pure-tone discrimination task where tones have to be categorized into targets and non-targets. While the interactions between networked neurons are thought to encode behavioral choice, it remains unclear how patterns of neuronal network activity indicate the transmission of task-relevant information within the network. To this end, we trained mice to behaviorally discriminate target vs. non-target pure-tones while we used in vivo 2-photon imaging to record neuronal population activity in primary auditory cortex layer 2/3. We found that during task performance, a specialized subset of neurons transiently encoded intersection information, i.e., sensory information that was used to inform behavioral choice. Granger causality analysis showed that these neurons formed functional networks in which task-relevant information was transmitted sequentially between neurons. Differences in network structure between target and non-target sounds encoded behavioral choice. Correct behavioral choices were associated with shorter timescale communication between neurons. In summary, we find that specialized neuronal populations in auditory cortex form functional networks during auditory task performance whose structures depend on both sensory input and behavioral choice.

neuroscience↗

bioRxiv2021

Direct Extraction of Signal and Noise Correlations from Two-Photon Calcium Imaging of Ensemble Neuronal Activity

Neuronal activity correlations are key to understanding how populations of neurons collectively encode information. While two-photon calcium imaging has created a unique opportunity to record the activity of large populations of neurons, existing methods for inferring correlations from these data face several challenges. First, the observations of spiking activity produced by two-photon imaging are temporally blurred and noisy. Secondly, even if the spiking data were perfectly recovered via deconvolution, inferring network-level features from binary spiking data is a challenging task due to the non-linear relation of neuronal spiking to endogenous and exogenous inputs. In this work, we propose a methodology to explicitly model and directly estimate signal and noise correlations from two-photon fluorescence observations, without requiring intermediate spike deconvolution. We provide theoretical guarantees on the performance of the proposed estimator and demonstrate its utility through applications to simulated and experimentally recorded data from the mouse auditory cortex.

neuroscience↗

bioRxiv2020

Phase separation by the Sterile Alpha Motif of Polyhomeotic compartmentalizes Polycomb Group proteins and enhances their activity

Polycomb Group (PcG) proteins organize chromatin at multiple scales to regulate gene expression. A conserved Sterile Alpha Motif (SAM) in the Polycomb Repressive Complex 1 (PRC1) subunit Polyhomeotic (Ph) is important for chromatin compaction and large-scale chromatin organization. Like many SAMs, Ph SAM forms helical head to tail polymers, and SAM-SAM interactions between chromatin-bound Ph/PRC1 are believed to compact chromatin and mediate long-range interactions. To understand mechanistically how this occurs, we analyzed the effects of Ph SAM on chromatin in vitro. We find that incubation of chromatin or DNA with a truncated Ph protein containing the SAM results in formation of concentrated, phase-separated condensates. Condensate formation depends on Ph SAM, and is enhanced by but not strictly dependent on, its polymerization activity. Ph SAM-dependent condensates can recruit PRC1 from extracts and enhance PRC1 ubiquitin ligase activity towards histone H2A. Overexpression of Ph with an intact SAM increases ubiquitylated H2A in cells. Thus, phase separation is an activity of the SAM, which, in the context of Ph, can mediate large-scale compaction of chromatin into biochemical compartments that facilitate histone modification.

biochemistry↗

bioRxiv2020

DNA binding reorganizes the intrinsically disordered C-terminal region of PSC in Drosophila PRC1

Polycomb Group (PcG) proteins regulate gene expression by modifying chromatin. A key PcG complex, Polycomb Repressive Complex 1 (PRC1), has two activities: a ubiquitin ligase activity for histone H2A, and a chromatin compacting activity. In Drosophila, the Posterior Sex Combs (PSC) subunit of PRC1 is central to both activities. The N-terminal homology region (HR) of PSC assembles into PRC1, including partnering with dRING to form the ubiquitin ligase for H2A. The intrinsically disordered C-terminal region of PSC (PSC-CTR) compacts chromatin, and inhibits chromatin remodeling and transcription in vitro. Both the PSC-HR and the PSC-CTR are essential in vivo. To understand how these two activities may be coordinated in PRC1, we used cross-linking mass spectrometry (XL-MS) to analyze the conformations of the PSC-CTR in PRC1 and how they change on binding DNA. XL-MS identifies interactions between the PSC-CTR and the core of PRC1, including between the PSC-CTR and PSC-HR. New contacts and overall more compacted PSC-CTR conformations are induced by DNA binding. Protein footprinting of accessible lysine residues in the PSC-CTR reveals an extended, bipartite candidate DNA/chromatin binding surface. Our data suggest a model in which DNA (or chromatin) follows a long path on the flexible PSC-CTR. Intramolecular interactions of the PSC-CTR detected by XL-MS can bring the high affinity DNA/chromatin binding region close to the core of PRC1 without disrupting the interface between the ubiquitin ligase and the nucleosome. Our approach may be applicable to understanding the global organization of other large IDRs that bind nucleic acids. HighlightsO_LIAn intrinsically disordered region (IDR) in Polycomb protein PSC compacts chromatin C_LIO_LICross-linking mass spectrometry (XL-MS) was used to analyze topology of the PSC IDR C_LIO_LIProtein footprinting suggests a bipartite DNA binding surface in the PSC IDR C_LIO_LIA model for the DNA-driven organization of the PSC IDR C_LIO_LICombining XL-MS and protein footprinting is a strategy to understand nucleic acid binding IDRs C_LI O_FIG O_LINKSMALLFIG WIDTH=149 HEIGHT=200 SRC="FIGDIR/small/130492v1_ufig1.gif" ALT="Figure 1"> View larger version (24K): org.highwire.dtl.DTLVardef@346c5dorg.highwire.dtl.DTLVardef@1b672b3org.highwire.dtl.DTLVardef@1247bfdorg.highwire.dtl.DTLVardef@48448e_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2018

Laminar profile of task-related plasticity in ferret primary auditory cortex

Rapid task-related plasticity is a neural correlate of selective attention in primary auditory cortex (A1). Top-down feedback from higher-order cortex may drive task-related plasticity in A1, characterized by enhanced neural representation of behaviorally meaningful sounds during auditory task performance. Since intracortical connectivity is greater within A1 layers 2/3 (L2/3) than in layers 4-6 (L4-6), we hypothesized that enhanced representation of behaviorally meaningful sounds might be greater in A1 L2/3 than L4-6. To test this hypothesis and study the laminar profile of task-related plasticity, we trained 2 ferrets to detect pure tones while we recorded laminar activity across a 1.8 mm depth in A1. In each experiment, we analyzed current-source densities (CSDs), high-gamma local field potentials (LFPs), and multi-unit spiking in response to identical acoustic stimuli during both passive listening and active task performance. We found that neural responses to auditory targets were enhanced during task performance, and target enhancement was greater in L2/3 than in L4-6. Spectrotemporal receptive fields (STRFs) computed from CSDs, high-gamma LFPs, and multi-unit spiking showed similar increases in auditory target selectivity, also greatest in L2/3. Our results suggest that activity within intracortical networks plays a key role in shaping the underlying neural mechanisms of selective attention.

neuroscience↗