Biology subjects

Williams, L. E.

Publications and source records attributed to Williams, L. E..

9 recordsLinked to original sources

bioRxiv2025

Hypoplasticity in sensory-driven neocortical circuits of the Fragile X syndrome mouse model

Sensory experience and perceptual learning modify the receptive field properties of cortical pyramidal neurons (PNs), primarily through long-term potentiation (LTP). Repetitive sensory stimulation or rhythmic whisker stimulation (RWS), at behaviourally relevant frequencies (8 Hz), can induce long-term potentiation (LTP) of excitatory synapses in typically developing mice in the somatosensory cortex (S1). Fragile X syndrome (FXS) is a leading single gene inherited form of intellectual disability and altered somatosensory processing is a prevalent feature. The Fragile X mouse model (Fmr1-/y mice) similarly exhibits altered somatosensory processing, including altered neuronal circuit function in S1. To assess if LTP in Layer (L) 2/3 PNs is intact upon changes in S1 circuit function we performed ex vivo whole-cell electrophysiology and in vivo two-photon calcium imaging of layer (L) 2/3 pyramidal neurons (PNs) in the S1 cortex of adult male Fragile X (Fmr1-/y) mice and typically developing (Fmr1+/y) control littermates. We found that plasticity induced by repetitive sensory stimulation was impaired in Fmr1-/y mice ex and in vivo compared to controls. L4-evoked synaptic responses were hyperexcitable in L2/3 PNs, consistent with circuit-level disinhibition. Despite this, baseline intrinsic spiking evoked by current steps remained largely unchanged and whisker-evoked activity appeared diminished in vivo, which may be consistent with findings of shortened axon initial segment (AIS) length. We also observed an increase in adaptation to repetitive stimulation in Fmr1-/y L2/3 PNs compared to controls, which may underlie failure to induce plasticity. These findings suggest that L2/3 PNs of S1 in Fmr1-/y mice are hypoplastic, potentially related to disrupted inhibitory control and rapid adaptation during repetitive sensory stimulation. Altogether, impaired LTP in the sensory cortex suggests that the receptive field properties of cortical PNs are less flexible and dynamic, which may contribute to altered somatosensory processing and reactivity in FXS.

neuroscience↗

bioRxiv2024

Repetitive sensory stimulation potentiates and recruits sensory-evoked cortical population activity

Sensory experience and learning are thought to be associated with plasticity of neocortical circuits. Repetitive sensory stimulation can induce long-term potentiation (LTP) of cortical excitatory synapses in anesthetized mice; however, it is unclear if these phenomena are associated with sustained changes in activity during wakefulness. Here we used time-lapse, calcium imaging of layer (L) 2/3 neurons in the primary somatosensory cortex (S1), in awake male mice, to assess the effects of a bout of rhythmic whisker stimulation (RWS) at a frequency by which rodents sample objects. We found that RWS induced a 1h-increase in whisker-evoked L2/3 neuronal activity. This was not observed for whiskers functionally connected to distant cortical columns. We also found that RWS altered whether individual neurons encoded subsequent stimulus representation by either being recruited or suppressed. Vasoactive intestinal-peptide-expressing (VIP) interneurons, which promote plasticity through disinhibition of pyramidal neurons, were found to exclusively elevate activity during RWS. These findings indicate that cortical neurons representation of sensory input can be modulated over hours through repetitive sensory stimulation, which may be gated by activation of disinhibitory circuits. SIGNIFICANCE STATEMENTSensory experience and learning are thought to be associated with the plasticity of cortical synaptic circuits. Here, we tested how repeated sensory stimulation changes subsequent sensory-evoked responses, using the mouse somatosensory cortex as a model. This cortical area processes, among others, sensory information from the whiskers. We found that rhythmic whisker stimulation potentiated excitatory neuronal activity for an hour, and identified a disinhibitory interneuron-mediated mechanism that could gate this plasticity. This work increases our understanding of sensory learning and experience-dependent plasticity processes by demonstrating that cortical representations of sensory input are dynamic and are effectively modulated by repeated sensory stimulation.

neuroscience↗

bioRxiv2024

Characterization of gelling agents in callus inducing media: Physical properties and their effect on callus development

In plant tissue culture, callus formation serves as a crucial mechanism for regenerating entire plants, enabling the differentiation of diverse tissues. Researchers have extensively studied the influence of media composition, particularly plant growth regulators, on callus behavior. However, the impact of the physical properties of the media, a well-established factor in mammalian cell studies, has received limited attention in the context of plant tissue culture. Previous research has highlighted the significance of gelling agents in affecting callus growth and differentiation, with agar, Phytagel, and Gelrite being the most used options. Despite their widespread use, a comprehensive comparison of their physical properties and their subsequent effects on callus behavior remains lacking. Our study seeks to bridge this gap by providing a thorough analysis of the physical properties of these gelling agents and their influence on callus induction and differentiation, offering valuable insights for researchers seeking to optimize plant tissue culture media for diverse applications. HighlightStudying the impact of gelling agents: Comprehensive analysis reveals how the physical properties of the growing media alters plant callus phenotype and differentiation in tissue culture.

plant biology↗

bioRxiv2020

Effects of relocation on Immunological and physiological measures in squirrel monkeys ( Saimiri boliviensis boliviensis)

In the present study, we have quantified the effects of transport, relocation and acclimate/adapt to their new surroundings on squirrel monkey. These responses are measured in blood samples obtained from squirrel monkeys, at different time points relative to their relocation from their old home to their new home. A variety of immunological assays are performed on the phenotype and function of peripheral blood mononuclear cells (PBMCs) in a group of squirrel monkeys that were transported by road for approximately 10 hours from one facility to another. Using a panel of human antibodies and a set of standardized human immune assays, we evaluated the phenotype of lymphocyte subsets by flow, mitogen-specific immune responses of PBMCs in vitro, and levels of cytokines at various time points including immediately before transport, immediately upon arrival, and after approximately 150 days of acclimation. We observed significant changes in T cells and subsets, NK and B cells (CD4+, CD8+, CD4+/CD8+, CD16+, and CD20+). Mitogen specific (e.g. PHA, PWM and LPS) proliferation responses, IFN-g by ELISPOT assay, and cytokines (IL-2, IL-4 and VEGF) significant changes were observed. Changes seen in the serum chemistry measurements mostly complement those seen in the hematology data. The specific goal was to empirically assess the effects of relocation stress in squirrel monkeys in terms of changes in the numbers and functions of various leukocyte subsets in the blood and the amount of time require for acclimating to their new environment. Such data will help to determine when newly arrived animals become available for use in research studies.

immunology↗

bioRxiv2020

Increased metal tolerance and bioaccumulation of zinc and cadmium in Chlamydomonas reinhardtii expressing a AtHMA4 C-terminal domain protein

The use of microalgal biomass for metal pollutant bioremediation might be improved by genetic engineering to modify the selectivity or capacity of metal biosorption. A plant cadmium (Cd) and zinc (Zn) transporter (AtHMA4) was used as a transgene to increase the ability of Chlamydomonas reinhardtii to tolerate 0.2 mM Cd and 0.3 mM Zn exposure. The transgenic cells showed increased accumulation and internalisation of both metals compared to wild type. AtHMA4 was expressed either as the full-length protein or just the C-terminal tail, which is known to have metal binding sites. Similar Cd and Zn tolerance and accumulation was observed with expression of either the full-length protein or C-terminal domain, suggesting that enhanced metal tolerance was mainly due to increased metal binding rather than metal transport. The effectiveness of the transgenic cells was further examined by immobilisation in calcium alginate to generate microalgal beads that could be added to a metal contaminated solution. Immobilisation maintained metal tolerance, while AtHMA4-expressing cells in alginate showed a concentration-dependent increase in metal biosorption that was significantly greater than alginate beads composed of wild type cells. This demonstrates that expressing AtHMA4 full-length or C-terminus has great potential as a strategy for bioremediation using microalgal biomass.Competing Interest StatementThe authors have declared no competing interest.View Full Text

plant biology↗

bioRxiv2019

Variation in genome context and predatory phenotypes between Bdellovibrio sp. NC01 isolated from soil and B. bacteriovorus type strain HD100

The range of naturally occurring variation in the ability of Bdellovibrio strains to attack and kill Gram-negative bacteria is not well understood. Defining phenotypic and associated genotypic variation among Bdellovibrio will clarify how divergent lineages within this genus impact microbial communities and will inform development of predatory bacteria as biocontrol agents to combat bacterial infections. We isolated Bdellovibrio sp. NC01 from soil and compared its genome and predatory phenotypes to B. bacteriovorus type strain HD100. Based on analysis of 16S rRNA gene sequences and average amino acid identity, NC01 belongs to a different species than HD100. Genome-wide comparisons and individual gene analyses indicated that eight NC01 genome regions were likely acquired by horizontal gene transfer (HGT), further supporting an important role for HGT in Bdellovibrio genome evolution. Within these regions, multiple protein-coding sequences were assigned predicted functions related to transcriptional regulation and transport; however, most were annotated as hypothetical proteins. Compared to HD100, NC01 has a limited prey range and kills E. coli ML35 less efficiently. Whereas HD100 drastically reduces the ML35 population and then maintains low prey population density, NC01 causes a smaller reduction in ML35, after which the prey population recovers, accompanied by a decrease in NC01. In addition, NC01 forms turbid plaques on lawns of ML35, in contrast to clear plaques formed by HD100. Characterizing variation in interactions between Bdellovibrio and Gram-negative bacteria, such as observed with NC01 and HD100, is important for understanding the ecological significance of predatory bacteria and evaluating their effectiveness in clinical applications. ImportanceBdellovibrio attack and kill Gram-negative bacteria; however, not all Bdellovibrio strains are equally efficient at killing the same Gram-negative bacteria. Defining how Bdellovibrio vary in predatory phenotypes and how this phenotypic variation relates to differences in genotype is important for understanding the ecological significance of predatory bacteria and evaluating their effectiveness in biocontrol of bacterial infections. We determined variation in genome content and predatory phenotypes, including prey range and predation efficiency, between Bdellovibrio sp. NC01 isolated from soil and B. bacteriovorus type strain HD100. NC01 is phylogenetically divergent from HD100, with eight regions of unique gene content likely acquired by horizontal gene transfer. Compared to HD100, the prey range of NC01 is limited, and it was less efficient at killing a strain of E. coli. These differences may have important implications for how each strain impacts microbial communities in different environments and for the effectiveness of each in clinical applications.

microbiology↗

bioRxiv2018

Comparative analysis of cellular immune responses in conventional and SPF Baboons (Papio spp.)

Baboons (papio spp.) have served as a successful model of human disease such as cardiac and respiratory, infectious, diabetes, genetics, immunology, aging, and xenotransplantation. The development of an immunologically defined specific-pathogen free (SPF) baboon model has further advanced research, especially with studies involving the immune system and immunosuppression. In this study, we compare normal immunological changes of peripheral blood mononuclear cell (PBMC) subsets, and their function in age-matched conventional and SPF baboons. Our results demonstrate that both groups have comparable numbers of different lymphocyte subsets, but there are phenotypic differences in central and effector memory T cells subsets that are more pronounced in the CD4+ T cells. Despite equal proportions of CD3+ T cells among the conventional and SPF baboon groups, PBMC show higher proliferative responses to mitogens PHA and PWM and higher IFN-{gamma} producing cells to Con A and PWM in the conventional group. Plasma levels of the inflammatory cytokine TNF- were significantly higher in SPF baboons. Exposure of PBMC from conventional baboons to various Toll like ligands (TLR ligands) TLR-3, TLR-4 and TLR-8 show higher IFN-{gamma} producing cells while PBMC from SPF baboons stimulated with TLR-5 and TLR-6 ligand show higher IFN-{gamma} producing cells. These findings suggest that while the lymphocyte subsets in conventional and SPF baboons share many phenotypic and functional similarities, specific differences exist in immune function of lymphocytes which could impact the quality and quantity of innate and adaptive immune responses. These differences should be considered for better experimental outcomes, specifically in studies measuring immunological endpoints.

immunology↗

bioRxiv2018

Higher-order thalamocortical inputs gate synaptic long-term potentiation via disinhibiton

Sensory experience and perceptual learning changes the receptive field properties of cortical pyramidal neurons, largely mediated by long-term potentiation (LTP) of synapses. The circuit mechanisms underlying cortical LTP remain unclear. In the mouse somatosensory cortex (S1), LTP can be elicited in layer (L) 2/3 pyramidal neurons by rhythmic whisker stimulation. We combined electrophysiology, optogenetics, and chemogenetics in thalamocortical slices to dissect the synaptic circuitry underlying this LTP. We found that projections from higher-order, posteriormedial thalamic complex (POm) to S1 are key to eliciting NMDAR-dependent LTP of intracortical synapses. Paired activation of intracortical and higher-order thalamocortical pathways increased vasoactive intestinal peptide (VIP) interneuron and decreased somatostatin (SST) interneuron activity, which was critical for inducing LTP. Our results reveal a novel circuit motif in which higher-order thalamic feedback gates plasticity of intracortical synapses in S1 via disinhibition. This motif may allow contextual feedback to shape synaptic circuits that process first-order sensory information.

neuroscience↗

bioRxiv2017

Prey range and genome evolution of Halobacteriovorax marinus predatory bacteria from an estuary

BackgroundHalobacteriovorax are saltwater-adapted predatory bacteria that attack Gram-negative bacteria and therefore may play an important role in shaping microbial communities. To understand the impact of Halobacteriovorax on ecosystems and develop them as biocontrol agents, it is important to characterize variation in predation phenotypes such as prey range and investigate the forces impacting Halobacteriovorax genome evolution across different phylogenetic distances.\n\nResultsWe isolated H. marinus BE01 from an estuary in Rhode Island using Vibrio from the same site as prey. Small, fast-moving attack phase BE01 cells attach to and invade prey cells, consistent with the intraperiplasmic predation strategy of H. marinus type strain SJ. BE01 is a prey generalist, forming plaques on Vibrio strains from the estuary as well as Pseudomonas from soil and E. coli. Genome analysis revealed that BE01 is very closely related to SJ, with extremely high conservation of gene order and amino acid sequences. Despite this similarity, we identified two regions of gene content difference that likely resulted from horizontal gene transfer. Analysis of modal codon usage frequencies supports the hypothesis that these regions were acquired from bacteria with different codon usage biases compared to Halobacteriovorax. In BE01, one of these regions includes genes associated with mobile genetic elements, such as a transposase not found in SJ and degraded remnants of an integrase occurring as a full-length gene in SJ. The corresponding region in SJ included unique mobile genetic element genes, such as a site-specific recombinase and bacteriophage-related genes not found in BE01. Acquired functions in BE01 include the dnd operon, which encodes a pathway for DNA modification that may protect DNA from nucleases, and a suite of genes involved in membrane synthesis and regulation of gene expression that was likely acquired from another Halobacteriovorax lineage.\n\nConclusionsOur results support previous observations that Halobacteriovorax prey on a broad range of Gram-negative bacteria. Genome analysis suggests strong selective pressure to maintain the genome in the H. marinus lineage represented by BE01 and SJ, although our results also provide further evidence that horizontal gene transfer plays an important role in genome evolution in predatory bacteria.

microbiology↗