Biology subjects

Bridges, C. M.

Publications and source records attributed to Bridges, C. M..

7 recordsLinked to original sources

bioRxiv2026

FGF signaling induces disease-associated oligodendrocyte states and drives myelin pathology

Myelin integrity is essential for normal central nervous system (CNS) function and is disrupted in neuroinflammatory and neurodegenerative disorders, including multiple sclerosis and Alzheimer's disease. In these settings, myelin-forming oligodendrocytes adopt a conserved disease-associated transcriptional state, termed disease-associated oligodendrocytes (DAOs). How DAOs arise, the signals that drive their induction, and whether they actively contribute to pathology remain poorly understood. Here we show that FGF signaling instructs mature oligodendrocytes to enter disease-associated states that are sufficient to trigger myelin pathology. By screening disease-linked secreted factors, we identify FGF1 and FGF2 as potent inducers of a DAO-like state in purified oligodendrocyte cultures, characterized by transcriptional reprogramming and myelin-membrane shedding. In vivo, activating oligodendrocyte FGF signaling is sufficient to elicit DAO programs and myelin disruption, whereas inhibiting FGF signaling suppresses DAO induction in a mouse model of multiple sclerosis. Finally, analysis of post-mortem multiple sclerosis tissue reveals a concordant DAO-like state associated with increased engagement of the FGF/FGFR axis. Collectively, these studies define a regulated mechanism of DAO formation linked to myelin disruption and position mature oligodendrocytes as active contributors to myelin pathology in CNS disease.

neuroscience↗

bioRxiv2023

Bacteriophage P22 SieA mediated superinfection exclusion

Many temperate phages encode prophage-expressed functions that interfere with superinfection of the host bacterium by external phages. Salmonella phage P22 has four such systems that are expressed from the prophage in a lysogen that are encoded by the c2 (repressor), gtrABC, sieA, and sieB genes. Here we report that the P22-encoded SieA protein is the only phage protein required for exclusion by the SieA system, and that it is an inner membrane protein that blocks DNA injection by P22 and its relatives, but has no effect on infection by other tailed phage types. The P22 virion injects its DNA through the host cell membranes and periplasm via a conduit assembled from three "ejection proteins" after their release from the virion. Phage P22 mutants were isolated that overcome the SieA block, and they have amino acid changes in the C-terminal regions of the gene 16 and 20 encoded ejection proteins. Three different single amino acid changes in these proteins are required to obtain nearly full resistance to SieA. Hybrid P22 phages that have phage HK620 ejection protein genes are also partially resistant to SieA. There are three sequence types of extant phage-encoded SieA proteins that are less than 30% identical to one another, yet comparison of two of these types found no differences in target specificity. Our data are consistent with a model in which the inner membrane protein SieA interferes with the assembly or function of the periplasmic gp20 and membrane-bound gp16 DNA delivery conduit. HIGHLIGHTSO_LIPhage P22 SieA protein blocks DNA injection by P22-like phages C_LIO_LISieA is an inner membrane protein C_LIO_LIHybrid P22 phages with phage HK620 ejection proteins partially escape SieA exclusion C_LIO_LISieA escape mutants of P22 alter the gp16 and 20 proteins that form the DNA ejection tube. C_LI

biochemistry↗

bioRxiv2022

Newly repopulated spinal cord microglia exhibit a unique transcriptome and coincide with sex-independent pain resolution

Microglia contribute to the initiation of pain, however, a translationally viable approach addressing how or when to modulate these cells remains elusive. We used a targeted, inducible, genetic microglial depletion strategy at both acute and acute-to-chronic transition phases in the clinically-relevant tibial fracture/casting pain model to determine the contribution of microglia to the initiation and maintenance of pain. We observed complete resolution of pain after transient microglial depletion at the acute-to-chronic phase, which coincided with the timeframe of full repopulation of microglia. These repopulated microglia were morphologically distinct from control microglia, signifying they may exhibit a unique transcriptome. RNA sequencing of repopulated spinal cord microglia identified genes of interest using weighted gene co-expression network analysis (WGCNA). We intersected these genes with a newly-generated single nuclei microglial dataset from human spinal cord dorsal horn and identified human-relevant genes that may ultimately promote pain resolution after injury. This work presents a novel approach to gene discovery in pain and provides comprehensive datasets for the development of future microglial-targeted therapeutics.

neuroscience↗

bioRxiv2021

Soil protists can actively redistribute beneficial bacteria along Medicago truncatula roots

The rhizosphere is the region of soil directly influenced by plant roots. The microbial community in the rhizosphere includes fungi, protists, and bacteria, all of which play a significant role in plant health. The beneficial bacterium Sinorhizobium meliloti infects growing root hairs on nitrogen-starved leguminous plants. Infection leads to the formation of a root nodule, where S. meliloti converts atmospheric nitrogen to ammonia, a usable form of nitrogen for plants. S. meliloti is often found in biofilms and travels slowly along the roots, leaving developing root hairs at the growing root tips uninfected. Soil protists are an important component of the rhizosphere system who prey on soil bacteria and have been known to egest undigested phagosomes. We show that the soil protist, Colpoda sp., can transport S. meliloti down Medicago truncatula roots. By using pseudo-3D soil microcosms, we directly observed the presence of fluorescently labelled S. meliloti along M. truncatula roots and tracked the displacement of the fluorescence signal over time. Two weeks after co-inoculation, this signal was detected 52 mm, on average, farther down the roots when Colpoda sp. was also present compared with the experimental treatment that contained bacteria but not protists. Direct counts also showed that protists are required for viable bacteria to reach the deeper sections of root systems in our microcosms. Facilitating bacterial transport may be an important mechanism whereby soil protists promote plant health. As a sustainable agriculture biotechnology, protist-facilitated transport has the potential to boost efficacy of bacterial inoculants, thereby helping growers avoid overuse of nitrogen fertilizers and enhance performance of climate-smart, no-till farming practices. ImportanceSoil protists are an important part of the microbial community in the rhizosphere. Plants grown with protists fare better than plants grown without protists. Mechanisms through which protists support plant health include nutrient cycling, alteration of the bacterial community through selective feeding, and consumption of plant pathogens. Here we provide data in support of an additional mechanism: protists act as transport vehicles for bacteria in soil. We show that protist-facilitated transport can deliver plant-beneficial bacteria to the growing tips of roots that may otherwise be sparsely inhabited with bacteria originating from a seed-associated inoculum. By co-inoculating Medicago truncatula roots with both S. meliloti, a nitrogen fixing legume symbiont, and Colpoda sp., a ciliated protist, we show substantial and statistically significant transport with depth and breadth of bacteria-associated fluorescence as well as transport of viable bacteria. Co-inoculation with shelf-stable encysted soil protists may be employed as a sustainable agriculture biotechnology to better distribute beneficial bacteria and enhance the performance of inoculants.

microbiology↗

bioRxiv2020

Development and application of aerobic, chemically defined media for Dysgonomonas

Members of Dysgonomonas are Gram-negative, non-motile, facultatively anaerobic coccobacilli originally described in relation to their isolation stool and wounds of human patients (CDC group DF-3). More recently Dysgonomonas have been found to be widely distributed in terrestrial environments and are particularly enriched in insect systems. Their prevalence in xylophagous insects such as termites and wood-feeding cockroaches, as well as in soil-fed microbial fuel cells, elicit interest in lignocellulose degradation and biofuel production, respectively. Their prevalence in mosquito and fruit fly have implications relating to symbiosis, host immunology and developmental biology. Additionally, their prevalence in termite, mosquito and nematode present novel opportunities for pest and vector control. Currently, the absolute growth requirements of Dysgonomonas are unknown, and they are cultured solely under anaerobic conditions on complex media containing blood, peptones, tryptones, and yeast, plant or meat extracts. Restrictive & undefined culturing conditions preclude physiological and genetic studies, and thus further understanding of metabolic potential. Here we describe the requirements for growth of termite-derived Dysgonomonas isolates and create parallel defined, minimal and complex media that permit vigorous and reliable aerobic growth. Furthermore, we show that these media can be used to easily enrich for Dysgonomonas isolates from complex and microbially-diverse environmental samples. Impact StatementMembers of the genus Dysgonomonas are increasingly prevalent in ecological, medical and biotechnological contexts. To the best of our knowledge, there are currently no formulations for chemically defined or minimal media for Dysgonomonas, and limited complex formulations that allow aerobic growth, particularly on solid media. We have created three parallel media formulations (complex, defined & minimal) that permit robust aerobic and anaerobic growth in liquid and agar-solidified media. These formulations remove the necessity for animal blood and expensive equipment such as anaerobic chambers, which can inhibit basic research by groups with biosafety and resource limitations.

microbiology↗

bioRxiv2020

Optogenetics in Sinorhizobium meliloti enables spatial control of exopolysaccharide production and biofilm structure

Microorganisms play a vital role in shaping the soil environment and enhancing plant growth by interacting with plant root systems. Due to the vast diversity of cell types involved, combined with dynamic and spatial heterogeneity, identifying the causal contribution of a defined factor, such as a microbial exopolysaccharide (EPS), remains elusive. Synthetic approaches that enable orthogonal control of microbial pathways are a promising means to dissect such complexity. Here we report the implementation of a synthetic, light-activated, transcriptional control platform in the nitrogen fixing soil bacterium Sinorhizobium meliloti. By fine tuning the system, we successfully achieved optical control of an EPS production pathway without significant basal expression under non-inducing (dark) conditions. Optical control of EPS recapitulated important behaviors such as a mucoid plate phenotype and formation of structured biofilms, enabling spatial control of biofilm structures in S. meliloti. The successful implementation of optically controlled gene expression in S. meliloti enables systematic investigation of how genotype and microenvironmental factors together shape phenotype in situ. SignificanceMicroorganisms are key players in sustaining the soil environment and plant growth. Symbiotic associations of soil microbes and plants provide a major source of nitrogen in agricultural systems, prevent water contamination from synthetic fertilizer application, and support crop growth in marginal soils. However, measuring the impact of microbial gene products on beneficial function remains a major challenge. This work provides a critical step toward addressing this challenge by implementing external gene regulation in a well characterized nitrogen fixing soil bacterium. We show that light exposure enables spatial and temporal control of the extracellular polysaccharide production functionality essential for symbiosis. Remote control of genes enables the benefits of candidate microorganisms to be systematically measured and enhanced within complex natural settings.

synthetic biology↗

bioRxiv2019

MEF2C hypofunction in neuronal and neuroimmune populations cooperate to produce MEF2C haploinsufficiency syndrome-like behaviors in mice

Microdeletions of the MEF2C gene are linked to a syndromic form of autism termed MEF2C haploinsufficiency syndrome (MCHS). Here, we show that MCHS-associated missense mutations cluster in the conserved DNA binding domain and disrupt MEF2C DNA binding. DNA binding-deficient global Mef2c heterozygous mice (Mef2c-Het) display numerous MCHS-like behaviors, including autism-related behaviors, as well as deficits in cortical excitatory synaptic transmission. We find that hundreds of genes are dysregulated in Mef2c-Het cortex, including significant enrichments of autism risk and excitatory neuron genes. In addition, we observe an enrichment of upregulated microglial genes, but not due to neuroinflammation in the Mef2c-Het cortex. Importantly, conditional Mef2c heterozygosity in forebrain excitatory neurons reproduces a subset of the Mef2c-Het phenotypes, while conditional Mef2c heterozygosity in microglia reproduces social deficits and repetitive behavior. Together our findings suggest that MEF2C regulates typical brain development and function through multiple cell types, including excitatory neuronal and neuroimmune populations.

neuroscience↗