Biology subjects

Allen, C. M.

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

3 recordsLinked to original sources

bioRxiv2026

Heatwaves strengthen historical contingency in yeast--bacterium interactions in floral nectar

Heatwaves can affect species abundances by changing how species interact in local communities. However, these effects remain poorly understood, especially when the outcome of species interactions is contingent on their arrival history. We studied how heatwaves affect interactions between the yeast Metschnikowia reukaufii and the bacterium Acinetobacter nectaris, both found in the floral nectar of Diplacus aurantiacus, a hummingbird-pollinated shrub native to California. Microbes were introduced to artificial nectar in different orders of arrival in the presence or absence of simulated two-day heatwaves. Heatwaves made yeast--bacterium interactions more contingent on arrival history, causing large variation in nectar acidity, a factor known to affect hummingbird preference. Specifically, in the absence of heatwaves, Acinetobacter became abundant regardless of arrival history, suppressing Metschnikowia and reducing nectar pH. In contrast, in the presence of heatwaves, Acinetobacter dominance depended on arrival history and heatwave timing. If Acinetobacter arrived after Metschnikowia during a heatwave, it was suppressed by Metschnikowia substantially enough to keep nectar pH at a high level. These results suggest that heatwaves shift species interactions from determinism to historical contingency, with taxonomic and functional consequences.

ecology↗

bioRxiv2026

Environmentally relevant depleted uranium exposure damages mitochondria, decreases cytosolic reductive capacity, and increases global DNA damage accumulation through a ROS-independent mechanism involving slingshot protein phosphatase 1b enrichment.

Depleted uranium (DU) is an environmental contaminant with a 30 {micro}g/L (ppb; parts per billion) EPA maximum contaminant level (MCL) for drinking water. The mining of uranium and use of DU in modern weapons underly human exposure that disproportionally impacts military and tribal communities in the United States. Uraniums radiotoxic characteristics are understood, but its chemical hazards much less so. In zebrafish (Danio rerio) and human cell cultures we test the hypothesis that exposure to DU negatively impacts cellular function and development through disruption of mitochondrial metabolism. Using a novel shrapnel model with TEM/SEM+EDS, we showed uranium microparticles caused proximity-dependent mitochondrial disruption. In waterborne exposure paradigms, larval movement was reduced and hatching delayed as a result of reduced movement and not enzyme deficiencies in response to 18 ppb DU, below the MCL. Increased DNA damage accumulation was detected in exposed larva and cells. DNA-damage quantitative PCR of DU-exposed larvae showed increased damage in the ahr1 locus (nuclear gene) and decreased mitochondrial DNA (mtDNA) copy number, but mtDNA damage levels varied across experiments. Mitochondrial function was assessed using a resazurin-based assay in the presence and absence of antioxidants and showed diminished cytoplasmic reductive capacity. DU exposure alone did not enrich antioxidant gene expression, contrasting with arsenic exposure, a known ROS-inducer and Nrf2-activator. Sulforaphane (SFN), a potent Nrf2-activator, did not blunt the effects of DU exposure, despite activation of antioxidant response element (ARE) genes (gstp and gss), but did blunt the effects of arsenic exposure. The most enriched transcript in DU-exposed larvae coded for slingshot protein phosphatase (ssh), further exploration revealed ssh1b as the zebrafish-specific ortholog activated in response to DU, and inhibition using an identified SSH1 inhibitor, Sennoside A, partially rescued the metabolic and hatching defects observed. Our data points to a cytotoxic mechanism in which DU disrupts mitochondrial function through ssh1b enrichment that impairs normal mitophagy, leading to decreased cellular reductive potential independent of either ROS production or ARE-activation. Our results suggest that health impacts from DU exposure may be directly linked to impaired mitochondrial functions.

pharmacology and toxicology↗

bioRxiv2018

Multiple functions for the catenin family member plakoglobin in cadherin-dependent adhesion, fibronectin matrix assembly and Xenopus gastrulation movements

Shaping an embryo requires tissue-scale cell rearrangements known as morphogenetic events. These force-dependent processes require cells to adhere to their neighbors, through cadherin-catenin complexes, and to their extracellular matrix substrates, through integrin-based focal contacts. Integrin receptors are not only important for attachment to the extracellular matrix, but also for its fibrillar assembly. Fibrillogenesis requires actomyosin contractility, regulated in part by cadherin-catenin complexes. One such catenin, plakoglobin, mediates the attachment of actin stress fibers to cadherin cytoplasmic tails through its interactions with actin-binding proteins. In Xenopus gastrulae, plakoglobin has been identified as an essential member in the force-induced collective migration of the mesendoderm tissue. In the current study, we have further characterized the role of plakoglobin in two additional morphogenetic processes, epiboly and convergent extension. Plakoglobin-deficient tadpoles are 40% shorter and gastrulae contain notochords that are 60% wider than stage-matched controls, indicating convergent extension defects. The radially intercalating ectoderm of morphant animal caps is nearly twice as thick as controls. Furthermore, morphant embryos exhibit a failure to assemble a fibronectin matrix at the notochord-somite-boundary or along the blastocoel roof. The loss of the fibronectin matrix, while not due to changes in overall patterning, is a result of a failure to assemble the soluble dimers into long fibrils. The force of attachment to a cadherin or fibronectin substrate is reduced in plakoglobin morphants, indicating defects in adhesion to both cadherin and fibronectin. These data suggest that plakoglobin regulates morphogenesis and fibronectin assembly through cell-cell and cell-matrix adhesion.

developmental biology↗