Biology subjects

Barnes, S. J.

Publications and source records attributed to Barnes, S. J..

4 recordsLinked to original sources

bioRxiv2022

Homeostatic regulation through strengthening of neuronal network-correlated synaptic inputs

Homeostatic regulation is essential for neuronal function. Several synaptic mechanisms of homeostatic plasticity have been described, but the functional properties of synapses involved in homeostasis are unknown. We used longitudinal two-photon functional imaging of dendritic spine calcium signals in visual and retrosplenial cortices of awake mice to quantify the sensory deprivation-induced changes in the responses of functionally identified spines. We found that spines whose activity selectively correlated with intrinsic network activity underwent TNF- dependent homeostatic increases in their response amplitudes, but spines identified as responsive to sensory stimulation did not. We observed an increase in the global sensory-evoked responses following sensory deprivation, despite the fact that the identified sensory inputs did not strengthen. Instead, global sensory-evoked responses correlated with the strength of network-correlated inputs. Our results suggest that homeostatic regulation of global responses is mediated through changes to intrinsic network-correlated inputs rather than changes to identified sensory inputs thought to drive sensory processing.

neuroscience↗

bioRxiv2022

Translocator protein is a marker of activated microglia in rodent models but not human neurodegenerative diseases

Microglial activation plays central roles in neuro-inflammatory and neurodegenerative diseases. Positron emission tomography (PET) targeting 18kDa Translocator Protein (TSPO) is widely used for localising inflammation in vivo, but its quantitative interpretation remains uncertain. We show that TSPO expression increases in activated microglia in mouse brain disease models but does not change in a non-human primate disease model or in common neurodegenerative and neuroinflammatory human diseases. We describe genetic divergence in the TSPO gene promoter, consistent with the hypothesis that the increase in TSPO expression in activated myeloid cells is unique to a subset of species within the Muroidea superfamily of rodents. We show that TSPO is mechanistically linked to classical pro-inflammatory myeloid cell function in rodents but not humans. These data emphasise that TSPO expression in human myeloid cells is related to different phenomena than in mice, and that TSPO PET reflects density of inflammatory cells rather than activation state.

neuroscience↗

bioRxiv2022

Cross-generational heritability analysis of physiological traits in Porites astreoides across an inshore-offshore gradient in the Lower Florida Keys

Estimating the heritable genetic variation in fitness-related traits is key to projecting the adaptive evolution of organisms in response to a changing environment. While heritability studies on reef-building corals to date support adaptive capacity, little is known about the dynamics of trait heritability across life stages in which distinct selective pressures can have long-lasting effects both within and across generations. In this study, we obtained heritability estimates for energetic and thermal stress response traits in larval, recruit, and adult Porites astreoides from two populations in the Lower Florida Keys. To induce bleaching phenotypes among individual families, larvae were exposed to a 4-day thermal stress at 32 {degrees}C, whereas adults and recruits received the same treatment for 22 days. Origin-dependent tolerance was observed in two life stages where offshore recruits lost more symbiont cells under heat than inshore recruits compared to their respective controls and heat-treated offshore adults suffered a greater loss in total protein content. Surprisingly, larvae appeared to be largely insensitive to heat regardless of origin. Broad sense heritability (H2) estimates varied greatly among traits and life stages, which may reflect changes in the relative importance of genetic and environmental variation throughout development. Notably, more than 80% of the variation in larval chlorophyll a concentration was attributed to genetic factors. The overall moderate to high H2 estimates measured here suggest these corals have considerable potential to adapt to environmental change.

ecology↗

bioRxiv2021

Ecophysiology of the cosmopolitan OM252 bacterioplankton (Gammaproteobacteria)

Among the thousands of species that comprise marine bacterioplankton communities, most remain functionally obscure. One key cosmopolitan group in this understudied majority is the OM252 clade of Gammaproteobacteria. Although frequently found in sequence data and even previously cultured, the diversity, metabolic potential, physiology, and distribution of this clade has not been thoroughly investigated. Here we examined these features of OM252 bacterioplankton using a newly isolated strain and genomes from publicly available databases. We demonstrated that this group constitutes a globally distributed novel genus (Candidatus Halomarinus), sister to Litoricola, comprising two subclades and multiple distinct species. OM252 organisms have small genomes (median 2.21 Mbp) and are predicted obligate aerobes capable of alternating between chemoorganoheterotrophic and chemolithotrophic growth using reduced sulfur compounds as electron donors, with subclade I genomes encoding the Calvin-Benson-Bassham cycle for carbon fixation. One representative strain of subclade I, LSUCC0096, had extensive halotolerance but a mesophilic temperature range for growth, with a maximum of 0.36 doublings/hr at 35{degrees}C. Cells were curved rod/spirillum-shaped, ~1.5 x 0.2 m. Growth on thiosulfate as the sole electron donor under autotrophic conditions was roughly one third that of heterotrophic growth, even though calculations indicated similar Gibbs energies for both catabolisms. These phenotypic data show that some Ca. Halomarinus organisms can switch between serving as carbon sources or sinks and indicate the likely anabolic cost of lithoautotrophic growth. Our results thus provide new hypotheses about the roles of these organisms in global biogeochemical cycling of carbon and sulfur. ImportanceMarine microbial communities are teeming with understudied taxa due to the sheer numbers of species in any given sample of seawater. One group, the OM252 clade of Gammaproteobacteria, has been identified in gene surveys from myriad locations, and one isolated organism has even been genome sequenced (HIMB30). However, further study of these organisms has not occurred. Using another isolated representative (strain LSUCC0096) and publicly available genome sequences from metagenomic and single-cell genomic datasets, we examined the diversity within the OM252 clade, the distribution of these taxa in the worlds oceans, reconstructed the predicted metabolism of the group, and quantified growth dynamics in LSUCC0096. Our results generate new knowledge about the previously enigmatic OM252 clade and point towards the importance of facultative chemolithoautotrophy for supporting some clades of ostensibly "heterotrophic" taxa.

microbiology↗