Biology subjects

Hill, R. A.

Publications and source records attributed to Hill, R. A..

15 recordsLinked to original sources

bioRxiv2026

Microglia detection and phagocytosis of dying neurons is regulated by CX3CR1

Neuronal cell death is a hallmark of many neurodegenerative diseases. Effective detection and clearance of cell debris generated during cell death events is essential to prevent a degenerative cascade. Brain resident microglia are responsible for performing these functions through complex cell-cell signaling involving both "find-me" and "eat-me" cues. To examine microglial responses to neuronal cell death in vivo, we investigated neuron/microglia CX3CL1/CX3CR1 signaling using intravital optical imaging in mouse cortex and a single-cell ablation technique called 2Phatal. We find that CX3CL1 aggregates as puncta on microglia and that this pattern is maintained when microglia engulf dying neurons. Additionally, disruption of this signaling via Cx3cr1 deletion when both few and many neurons are dying leads to delayed cell corpse clearance, partly due to a delay in microglial engagement with the dying cells. Overall, our work uncovers a precise role for CX3CL1/CX3CR1 signaling in regulating the microglial response to dying neocortical neurons.

neuroscience↗

bioRxiv2026

Dying oligodendrocytes persist without mitochondria

Myelin is an insulating, multi-layered membrane that supports axonal integrity and neural communication. Different stressors impair myelinating oligodendrocytes, leading to demyelination, inflammation, and neurodegeneration. The intracellular processes underlying oligodendrocyte degeneration and death are unclear. Here, using optically targeted DNA damage that causes single-cell demyelination, we reveal that injured mature oligodendrocytes lose mitochondria within days and persist without them for weeks to months before cell death. This differs from other oligodendrocyte lineage cells, which exhibit acute mitochondrial changes followed by rapid cell death. Conditional deletion of the mitochondrial-related gene, Fis1, in mature oligodendrocytes, similarly causes acute loss of mitochondria and prolonged cell death. The unique cell death is characterized by nuclear changes, intracellular stress, and markers of disease-associated oligodendrocytes. Thus, mitochondrial loss may be an early marker of oligodendrocyte pathology, and mitochondrial quality control is required for oligodendrocyte and myelin homeostasis.

neuroscience↗

bioRxiv2024

Contrasting impacts of invasive Opuntia cacti on mammal habitat use

Biological invasions impact ecosystems worldwide, including through changing the behaviour of native species. Here, we used camera traps to investigate the effects of invasive Opuntia cacti on the habitat use of twelve mammal species in Laikipia County, Kenya, an internationally important region of mammalian biodiversity. We found that Opuntia impacted mammal occupancy and activity, but the strength and direction of the effects varied among species and between seasons, and depended on the spatial scale at which Opuntia was considered. Notably, we observed consistent positive effects for olive baboons and elephants, two major consumers of Opuntia fruit. We also observed seasonally varying effects on the occupancy of two key grazers: Grevys zebra and plains zebra. As well as having important implications for mammal conservation, ecosystem functioning, and the future spread of Opuntia, our findings highlight behavioural changes in large mammals as a potentially important pathway through which invasive species impact ecosystems.

ecology↗

bioRxiv2024

Predicting woodland bird species habitat with multi-temporal and multisensor remote sensing data

Remote sensing data capture ecologically important information that can be used to characterize, model and predict bird habitat. This study implements fusion techniques using Random Forests (RF) with spectral Landsat data and structural airborne laser scanning (ALS) data to scale habitat attributes through time and to characterize habitat for four bird species in dynamic young forest environments in the United Kingdom. We use multi-temporal (2000, 2005, 2012/13, 2015) multi-sensor (Landsat and ALS) data to (i) predict structural attributes via pixel-level fusion at 30 metre spatial resolution, (ii) model bird habitat via object-level fusion and compare with models based on ALS, Landsat and predicted structural attributes, and (iii) predict bird habitat through time (i.e., predict 2015 habitat based on 2000-2012 data). First, we found that models predicting mean height from spectral information had the highest accuracy, whilst maximum height, standard deviation of heights, foliage height diversity, canopy cover and canopy relief ratio had good accuracy, and entropy had low accuracy. The green band and the normalized burn ratio (NBR) were consistently important for prediction, with the red and shortwave infrared (SWIR) 1 bands also important. For all structural variables, high values were underpredicted and low values were overpredicted. Second, for Blue Tit (Cyanistes caeruleus) and Chaffinch (Fringilla coelebs), the most accurate model employed Landsat data, while object-level fusion performed best for Chiffchaff (Phylloscopus collybita) and Willow Warbler (Phylloscopus trochilus). ALS mean, maximum and standard deviation of heights and Landsat tasseled cap transformations (TCT) (i.e., wetness, greenness and brightness) were ranked as important to all species across various models. Third, we used our models to predict presence in 2015 and implemented a spatial intersection approach to assess the predictive accuracy for each species. Blue Tit and Willow Warbler presences were well predicted with the Landsat, ALS, and objectlevel fusion models. Chaffinch and Chiffchaff presences were best predicted with the ALS model. Predictions based on pixel-level predicted structure surfaces had low accuracy but were acceptable for Chaffinch and Willow Warbler. This study is significant as it provides guidance for Landsat and ALS data application and fusion in habitat modelling. Our results highlight the need to use appropriate remote sensing data for each study species based on their ecology. Object-level data fusion improved habitat characterization for all species relative to ALS, but not to Landsat for Blue Tit and Chaffinch. Pixel-level fusion for predicting structural attributes in years where ALS data are note available is increasingly being used in modelling but may not adequately represent within-patch wildlife habitat. Finally, incorporating predicted surfaces generated through pixel-level fusion in our habitat models yielded low accuracy. HighlightsO_LIWe used object- and pixel-level fusion with ALS and Landsat to examine bird habitat C_LIO_LIPixel-level fusion predicted surfaces yielded low accuracy in habitat models C_LIO_LIBest models: Landsat (Blue Tit, Chaffinch); fusion (Chiffchaff, Willow Warbler) C_LIO_LIBest prediction: ALS (Chaffinch, Chiffchaff) C_LIO_LIBest prediction: ALS, Landsat, object-level fusion (Blue Tit, Willow Warbler) C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=127 SRC="FIGDIR/small/625964v1_ufig1.gif" ALT="Figure 1"> View larger version (77K): org.highwire.dtl.DTLVardef@c52aaeorg.highwire.dtl.DTLVardef@75133dorg.highwire.dtl.DTLVardef@420d1aorg.highwire.dtl.DTLVardef@6a5f8a_HPS_FORMAT_FIGEXP M_FIG C_FIG

ecology↗

bioRxiv2024

Transient upregulation of procaspase-3 during oligodendrocyte fate decisions

Oligodendrocytes are generated throughout life and in neurodegenerative conditions from brain resident oligodendrocyte precursor cells (OPCs). The transition from OPC to oligodendrocyte involves a complex cascade of molecular and morphological states that position the cell to make a fate decision to integrate as a myelinating oligodendrocyte or die through apoptosis. Oligodendrocyte maturation impacts the cell death mechanisms that occur in degenerative conditions, but it is unclear if and how the cell death machinery changes as OPCs transition into oligodendrocytes. Here, we discovered that differentiating oligodendrocytes transiently upregulate the zymogen procaspase-3, equipping these cells to make a survival decision during differentiation. Pharmacological inhibition of caspase-3 decreases oligodendrocyte density, indicating that procaspase-3 upregulation promotes differentiation. Moreover, using procaspase-3 as a marker, we show that oligodendrocyte differentiation continues in the aging cortex and white matter. Taken together, our data establish procaspase-3 as a differentiating oligodendrocyte marker and provide insight into the underlying mechanisms occurring during the decision to integrate or die.

neuroscience↗

bioRxiv2024

Mitochondria are absent from microglial processes performing surveillance, chemotaxis, and phagocytic engulfment

Microglia continually surveil the brain allowing for rapid detection of tissue damage or infection. Microglial metabolism is linked to tissue homeostasis, yet how mitochondria are subcellularly partitioned in microglia and dynamically reorganize during surveillance, injury responses, and phagocytic engulfment in the intact brain are not known. Here, we performed intravital imaging of microglia mitochondria, revealing that microglial processes diverge, with some containing multiple mitochondria while others are completely void. Microglial processes that engage in minute-to-minute surveillance typically do not have mitochondria. Moreover, unlike process surveillance, mitochondrial motility does not change with animal anesthesia. Likewise, the processes that acutely chemoattract to a lesion site or initially engage with a neuron undergoing programmed cell death do not contain mitochondria. Rather, microglia mitochondria have a delayed arrival into the responding cell processes. Thus, there is subcellular heterogeneity of mitochondrial partitioning and asymmetry between mitochondrial localization and cell process motility or acute damage responses.

neuroscience↗

bioRxiv2024

finsyncR, an R package to synchronize 27 years of fish and invertebrate data across the United States

The United States government collects some of the most comprehensive data on freshwater systems in existence, but barriers exist for new users to apply these data without institutional guidance. finsyncR (fish and invertebrate synchronizer in R) is an R package that streamlines the process of acquiring, processing, and integrating fish and macroinvertebrate datasets collected in streams and rivers, increasing access to cleaned data and ensuring straightforward application of the data. The data sources are the US Environmental Protection Agencys National River and Streams Assessment and US Geological Surveys BioData. The resulting datasets span 27 years (1993 to 2019) and include 8,115 sites, 15,169 sampling events, 963 macroinvertebrate genera, and 687 fish species. We document common challenges to working with these data including understanding sampling designs, harmonizing taxonomy, calculating densities and standardized abundances, accounting for differences in sampling effort, and considering improvements in taxonomic identifications. We anticipate this package will spur research exploring changes in fish and macroinvertebrate communities across space and time and the causes and consequences of those changes.

ecology↗

bioRxiv2023

Microglial phagocytosis of single dying oligodendrocytes is mediated by CX3CR1 but not MERTK

Oligodendrocyte death is common in aging and neurodegenerative diseases. In these conditions, single dying oligodendrocytes must be efficiently removed to allow remyelination and prevent a feed-forward degenerative cascade. Here we used a single-cell cortical demyelination model combined with longitudinal intravital imaging of dual-labeled transgenic mice to investigate the cellular dynamics underlying how brain resident microglia remove these cellular debris. Following phagocytic engagement, single microglia cleared the targeted oligodendrocyte and its myelin sheaths in one day via a precise, rapid, and stereotyped sequence. Deletion of the fractalkine receptor, CX3CR1, delayed microglia engagement with the cell soma but unexpectedly did not affect the clearance of myelin sheaths. Furthermore, and in contrast to previous reports in other demyelination models, deletion of the phosphatidylserine receptor, MERTK, did not affect oligodendrocyte or myelin sheath clearance. Thus, distinct molecular signals are used to detect, engage, and clear sub-compartments of dying oligodendrocytes to maintain tissue homeostasis.

neuroscience↗

bioRxiv2023

Mitochondrial network reorganization and transient expansion during oligodendrocyte generation

Oligodendrocyte precursor cells (OPCs) give rise to myelinating oligodendrocytes of the central nervous system. This process persists throughout life and is essential for recovery from neurodegeneration. To better understand the cellular checkpoints that occur during oligodendrogenesis, we determined the mitochondrial distribution and morphometrics across the oligodendrocyte lineage in mouse and human cerebral cortex. During oligodendrocyte generation, mitochondrial content expanded concurrently with a change in subcellular partitioning towards the distal processes. These changes were followed by an abrupt loss of mitochondria in the oligodendrocyte processes and myelin, coinciding with sheath compaction. This reorganization and extensive expansion and depletion took 3 days. Oligodendrocyte mitochondria were stationary over days while OPC mitochondrial motility was modulated by animal arousal state within minutes. Aged OPCs also displayed decreased mitochondrial size, content, and motility. Thus, mitochondrial dynamics are linked to oligodendrocyte generation, dynamically modified by their local microenvironment, and altered in the aging brain.

neuroscience↗

bioRxiv2023

Oligodendrocyte maturation alters the cell death mechanisms that cause demyelination

Myelinating oligodendrocytes die in human disease and early in aging. Despite this, little is known about the mechanisms that govern cell death across the oligodendrocyte lineage. Here we used a combination of intravital imaging, single-cell ablation, and cuprizone intoxication to show that oligodendrocyte maturation dictates the dynamics and mechanisms of death. After single-cell genotoxic damage, oligodendrocyte precursor cells underwent programmed cell death within hours, while mature oligodendrocytes died weeks after the same acute damage. Targeting single cells that were actively undergoing oligodendrocyte generation revealed that a switch in the temporal dynamics and morphological progression of death occurs during differentiation. Consistent with this, cuprizone intoxication initiated a caspase-3-dependent form of rapid cell death in differentiating oligodendrocytes, while mature oligodendrocytes never activated this executioner caspase and exhibited delayed cell death initiation. Thus, oligodendrocyte maturation plays a key role in determining the mechanism of death a cell undergoes in response to the same insult. This means that different strategies are likely necessary to confer protection to the entire oligodendrocyte lineage to enable myelin preservation and facilitate the integration of new oligodendrocytes in aging and disease.

neuroscience↗

bioRxiv2023

TREM2 and APOE do not modulate phagocytic clearance of dying cells in the live mammalian brain

TREM2 and APOE are two major risk factors for Alzheimers disease (AD) that have been proposed to play crucial roles in microglia pathophysiology by affecting their ability to phagocytose cellular debris or aggregated proteins. In this study, we investigated for the first time the impact of TREM2 and APOE on the removal of dying neurons in the live brain by implementing a targeted photochemical method for programmed cell death induction combined with high-resolution two-photon imaging. Our findings showed that the deletion of either TREM2 or APOE did not affect the dynamics of microglia engagement with dying neurons or their efficiency in phagocytosing corpses. Interestingly, while microglia that encapsulate amyloid deposits were capable of phagocytosing dying cells without disengaging from plaques or moving their cell bodies; in the absence of TREM2, microglia cell bodies were observed to readily migrate towards dying cells, further disengaging from plaques. Our data suggest that TREM2 and APOE variants are unlikely to increase risk of AD through impaired corpse phagocytosis. SummaryHigh-resolution two-photon imaging of programmed cell death in the live mouse brain reveals that neither TREM2 nor APOE modulate microglia phagocytosis of neuronal corpses. However, TREM2 regulates microglia migratory behavior towards dying cells in the vicinity of amyloid plaques.

neuroscience↗

bioRxiv2022

Identification of potential inhibitors of cutaneous Melanoma and Non-Melanoma skin cancer cells through in vitro and in silico screening of a small library of Phenolic compounds

Melanoma and non-melanoma skin cancers are the most-lethal and commonest forms of skin cancers, that affecting one-fifth of the US population. With the aim of identifying new lead compounds as starting point for attaining cost-effective therapies, a small library of about 90 molecules was screened in vitro against A375, SKMEL-28, A431, SCC-12 skin cancer cell lines. About 35 of them, mainly dihydroquinolines, C-C and C-N linked biphenyls, and substituted methylgallate or aniline derivatives, displayed low-micromolar range activities, primarily against the A431 and SCC-12 squamous carcinoma cell lines, with only a handful of these compounds displaying any activity against the A375 and SKMEL-28 melanoma cell lines. Compounds 11 (A431: IC50 = 5.0 {micro}M, SCC-12: IC50 = 2.9 {micro}M, SKMEL-28: IC50 = 4.9 {micro}M, A375: IC50 = 6.7 {micro}M) and 13 (A431: IC50 = 5.0 {micro}M, SCC-12: IC50 = 3.3 {micro}M, SKMEL-28: IC50 = 13.8 {micro}M, A375: IC50 = 17.1 {micro}M) were the most active across all these cell lines. Furthermore, many of the hit compounds showed little to no activity against mammalian nontumorigenic immortalized HaCaT cells, with a far better selectivity index than cisplatin (a well-known anticancer agent used as a positive control). Compounds 11 and 13 significantly and dose-dependently induced apoptosis of SCC-12 and SK-MEL-28 cells as evidenced by the downregulation of Bcl-2 and upregulation of Bax protein expression levels, and by cleaved caspase-3, caspase-9 and PARP levels. Both agents also significantly reduced scratch wound healing, colony formation, and activated expression levels of major cancer molecular targets such as RSK/AKT/ERK1/2 and S6K1. To provide a better attribute profile for each of the hit molecules, in-silico target(s) prediction, pharmacokinetic and ADMET studies are also reported, together with some preliminary structure-activity relationship outlines. The SwissTargetPrediction web-based tool identified CDK8, CLK4, nuclear receptor ROR, tyrosine protein-kinase Fyn/LCK, ROCK1/2, and PARP, all of which are dysregulated in skin cancers, as likely targets for these hit compounds. Furthermore, the SwissADME web_tool predicted these compounds to exhibit high GI tract absorption, good skin permeation, and a viable biodegradability profile. To summarize, these data highlight the promising anticancer potential of these small molecules leads, warranting further investigation and/or optimization towards obtaining clinical candidates for combatting both melanoma and non-melanoma skin cancers.

pharmacology and toxicology↗

bioRxiv2020

Age and axon-specific forms of cortical remyelination by divergent populations of NG2-glia

Myelin is critical for neural circuit function and its destruction is widespread in neurodegenerative disease and aging. In these conditions, homeostatic repair mechanisms initiate oligodendrocyte replacement by resident progenitor cells called NG2-glia. To investigate the cellular dynamics of this repair we developed a novel demyelination model by combining intravital myelin imaging with a targeted single-cell ablation technique called 2Phatal. Oligodendrocyte 2Phatal activated a stereotyped degeneration cascade which triggered remyelination by local NG2-glia. Remyelination efficiency was dependent on initial myelin patterning and dynamic imaging revealed rapid repair mechanisms resulting in near-seamless transitions between myelin loss and repair. A subset of morphologically complex NG2-glia executed this remyelination, pointing towards unrecognized functional diversity within this population. Age-related demyelination mirrored the degenerative cascade observed with 2Phatal, while remyelination in aging was defective due to failed oligodendrogenesis. Thus, oligodendrocyte 2Phatal revealed cellular diversity within the oligodendrocyte lineage and uncovered novel forms of rapid remyelination.

neuroscience↗

bioRxiv2020

Aberrant axonal pathfinding and exuberant myelination in an inducible model of neocortical heterotopia

Neocortical heterotopia consist of ectopic neuronal clusters that are frequently found in individuals with cognitive disability and epilepsy. However, their pathogenesis remains poorly understood due in part to a lack of tractable animal models. We have developed an inducible model of focal heterotopia that enables their precise spatiotemporal control and high-resolution optical imaging in live mice. Here we report that heterotopia are associated with striking patterns of hypermyelinated and circumferentially projecting axons around neuronal clusters. Despite their aberrant axonal patterns, in vivo calcium imaging revealed that heterotopic neurons remain functionally connected to other brain regions, highlighting their potential to influence global neural networks. These aberrant patterns only form when heterotopia are induced during a critical embryonic temporal window, but not in early postnatal development. Our model provides a new way to investigate heterotopia formation in vivo and revealed features suggesting the existence of developmentally-modulated, neuron-derived axon guidance and myelination factors.

developmental biology↗

bioRxiv2018

SP1433-1438 operon of Streptococcuspneumoniae regulates metal homeostasis and cellular metabolism during zinc-stress

Streptococcus pneumoniae colonizes the mucosa of the human nasopharynx and is a leading cause of community-acquired pneumonia, acute otitis media, and bacterial meningitis. Metal ion homeostasis is vital to the survival of this pathogen and contributes significantly to both colonization and invasive disease. Microarray and qRT-PCR analysis revealed an upregulation of an uncharacterized operon (SP1433-1438) in pneumococci subjected to metal-chelation by N,N,N,N-tetrakis-(2-Pyridylmethyl)ethylenediamine (TPEN). Supplementation of either zinc or cobalt following TPEN treatment drastically abrogated induction. BLAST analysis predicted this operon to encode two ABC-transporters, sharing homology to a multidrug resistance system (SP1434-1435) and an energy-coupling factor (ECF) transport system (SP1436-1438). Inductively coupled plasma mass spectrometry (ICP-MS) analysis indicated changes in intracellular concentrations of iron, zinc, and manganese ions in a {Delta}1434-8 strain compared to parental T4R. Analysis of the secreted metabolomic profile of the T4R and {Delta}1434-8 strains identified significant changes in pneumococcal glycolytic pathways, indicating a shift towards increased production of acetate. Additionally, proteomic analysis revealed 41 differentially expressed proteins in the {Delta}1434-8 strain, with roughly 20% of them regulated by the global catabolite repressor, CcpA. Based on these findings, we propose that the SP1433-1438 operon is largely involved in the central metabolism of S. pneumoniae during zinc-limitation.\n\nImportanceMetal sequestration is a common strategy utilized by the host immune response as well as antibiotics such as vancomycin to kill invading bacterial pathogens (1). However, pneumococcus is still able to thrive under zinc-limiting conditions. This study describes a previously uncharacterized operon encoding two ABC transport systems that are strongly induced during zinc-limiting conditions. This operon was found to be regulated by a zinc-dependent regulator (SP1433) that functions independently of the overarching AdcR regulon. We have additionally utilized a 2D-NMR approach to analyze the secreted metabolome and have employed proteomic analysis to identify a role for these systems in the maintenance of cellular metabolism. This study provides new information on how Streptococcus pneumoniae responds and adapts to zinc-limiting conditions.

microbiology↗