Biology subjects

Keller, S. R.

Publications and source records attributed to Keller, S. R..

13 recordsLinked to original sources

bioRxiv2026

Dynamic Fluoroleucine PET Detects Impaired Cardiac Leucine Uptake Before Hypertensive Left Ventricular Hypertrophy Develops

PurposeLeft ventricular hypertrophy (LVH) is a major complication of chronic hypertension and an independent risk factor for cardiovascular morbidity and mortality. There are currently no clinically validated markers available to identify hypertensive individuals at risk for developing LVH. In hearts of hypertensive rats, we previously described metabolic changes that precede LVH development, including in branched-chain amino acid (BCAA) metabolism. This study investigated whether cardiac leucine uptake, measured with dynamic 5-[18F]fluoroleucine positron emission tomography-computed tomography ([18F]FLE-PET/CT), was impaired and could serve as an in vivo marker for hypertension-induced LVH development. ProceduresWe synthesized [18F]FLE following established radiochemistry protocols and performed dynamic [18F]FLE-PET/CT imaging in 3-month-old spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) control rats (n = 4 per group). Cardiac magnetic resonance (CMR) imaging was conducted on the same animals for structural co-registration. A dual-output reversible two-tissue compartment model with spill-over (SP) and partial volume (PV) corrections was developed to quantify the first-pass rate constant (K1) and total distribution volume (Vt = K1/k2) for [18F]FLE. Protein expression of L-type amino acid transporter 1 (LAT1) and branched-chain keto acid dehydrogenase (BCKDH) phosphorylation status were assessed by immunoblotting of isolated heart tissue. ResultsSHR demonstrated markedly lower first-pass leucine uptake rates (K1) and total distribution volumes (Vt) compared with WKY rats, consistent with reduced cardiac BCAA uptake. Concurrently, LAT1 (SLC7A5) expression was significantly reduced in SHR hearts compatible with decreased leucine uptake. Elevated BCKDH phosphorylation at Ser293 in SHR hearts indicated diminished BCKDH enzymatic activity and impaired BCAA catabolism. ConclusionsDynamic cardiac [18F]FLE-PET imaging successfully detects decreased leucine uptake in hypertensive rat hearts at 3 months of age, before LVH is established at 5 months. Reduced cardiac leucine uptake may thus serve as a surrogate marker for impaired cardiac BCAA metabolism and early in vivo indicator of cardiometabolic dysfunction that precedes LVH. The imaging approach holds translational potential for identifying hypertensive patients at risk for LVH progression.

bioengineering↗

bioRxiv2026

Phenotypic plasticity evolved for climate variability constrains performance under climate warming

Phenotypic plasticity allows plants to rapidly respond to changing environments without the need for evolutionary change or migration. While selection can create variation in plasticity across natural populations, these responses are not adaptive in all environments. To predict whether plasticity will be adaptive requires evaluation of its fitness effects across a range of environments, including novel ones. Here, we test how traits and their plasticity vary for genotypes collected across a natural hybrid zone between two tree species with contrasting climatic niches. Fast-growing Populus trichocarpa inhabits maritime environments with relatively warm and stable temperatures, while P. balsamifera inhabits continental environments with cold winters and large temperature variance throughout the year. We planted 44 clonally replicated genotypes into thirteen common gardens and measured vegetative phenology, leaf morphology, stomata morphology and conductance, and photochemistry. Overall, genotypes from colder, more continental environments exhibited higher plasticity. P. balsamifera ancestry was associated with increased plasticity in timing of fall phenology, stomatal conductance, and leaf mass per unit area. We assessed the effects of trait plasticity on fitness estimated as yearly growth across common gardens and found that the plasticity-fitness relationship was often garden-specific, indicating that the planting environment did not consistently mediate plasticity-fitness relationships. When the effects of trait plasticity on growth varied by garden temperature, higher plasticity generally had neutral or negative associations with growth in warmer environments. These results suggest that elevated plasticity evolved in a P. balsamifera genomic background as part of a climate generalist strategy to seasonal temperature variability, but that there is a trade-off between plasticity and growth in warmer environments. Consequently, less-plastic but warm-adapted P. trichocarpa genotypes are likely to have a fitness advantage under warming climates. These results demonstrate that plasticity may sometimes be maladaptive and will not be universally beneficial in a warming world.

evolutionary biology↗

bioRxiv2025

Variation in responses to temperature across admixed genotypes of Populus trichocarpa x P. balsamifera predict geographic shifts in regions where hybrids are favored

O_LIPlastic responses of plants to their environment vary as a result of genetic differentiation within and among species. To accurately predict rangewide responses to climate change, it is necessary to characterize genotype-specific reaction norms across the continuum of historic and future climate conditions comprising a species range. C_LIO_LIThe North American hybrid zone of Populus trichocarpa and P. balsamifera represents a natural system that has been shaped by climate, geography, and introgression. We leverage a dataset containing 45 clonal genotypes from this natural hybrid zone, planted across 17 replicated common garden experiments spanning a broad climatic range. Growth and mortality were measured over two years, enabling us to model reaction norms for each genotype across these tested environments. C_LIO_LISpecies ancestry and intraspecific genomic variation significantly influenced growth across environments, with genotypic variation in reaction norms reflecting a trade-off between cold tolerance and growth. Using modeled reaction norms for each genotype, we predicted that genotypes with more P. trichocarpa ancestry may gain an advantage under warmer climates. C_LIO_LISpatial shifts of the hybrid zone could facilitate the spread of beneficial alleles into novel climates. These results highlight that genotypic variation in responses to temperature will have landscape-level effects. C_LI

evolutionary biology↗

bioRxiv2025

Protein Phosphatase 2A Subunit B55 Alpha is Required for Angiotensin Type 2 Receptor Elicited Natriuresis

BackgroundAngiotensin type 2 receptor (AT2R) activation promotes natriuresis in renal proximal tubule cells (RPTCs) counteracting sodium retention stimulated by the AT1R. Early signaling events mediating the natriuretic response with AT2R activation in RPTCs are currently unknown. Our previous research suggested protein phosphatase 2A (PP2A) functions downstream of the AT2R. In this study, we investigated the interaction of PP2A regulatory subunit B55 with the AT2R and requirement for B55 in AT2R signaling and natriuresis. Methods and ResultsRats were subjected to renal interstitial (RI) infusion of vehicle or Compound 21 (C21), a non-peptide specific AT2R agonist, and kidney sections were probed for interactions between PP2A subunits and the AT2R using a proximity ligation assay. A dramatic 6-fold increase in AT2R-B55 interaction in apical brush border membranes of RPTCs was observed with C21 stimulation. In vitro binding of purified AT2R and B55 supported a direct interaction between these two proteins. To determine the requirement for B55 in renal AT2R signaling, siRNA targeting B55 was administered to rats in vivo by RI infusion which resulted in a [~]70% decrease in B55 in RPTCs but not distal tubules. In rats with B55 knockdown in RPTCs, natriuresis in response to C21 was abolished. Simultaneously, C21-elicited AT2R redistribution to and sodium transporter Na+/H+ exchanger-3 (NHE3) retrieval from apical brush border membranes was lost, as observed with confocal immunofluorescence microscopy. Consistent with impaired AT2R signaling, B55 knockdown prevented c-Src phosphorylation in response to C21. B55 knockdown also led to a dramatic 4 to 6-fold increase in AT2R co-localization with the lysosomal marker LAMP1, and a 50% reduction in AT2R co-localization with EEA1 and Rab 7, markers for early and late endosomes, respectively. ConclusionsPP2A B55 directly binds to the activated AT2R and is required for AT2R-elicited natriuresis, AT2R signaling and intracellular trafficking in RPTCs.

physiology↗

bioRxiv2023

Climate and geography shape hybrid zone dynamics across space and time: insights from Populus trichocarpa x P. balsamifera

Population demographic changes, alongside landscape, geographic, and climate heterogeneity, can influence the timing, stability, and extent of introgression where species hybridize. Thus, quantifying interactions across diverged lineages, and the relative contributions of interspecific genetic exchange and selection to divergence at the genome-wide level is needed to better understand the drivers of hybrid zone formation and maintenance. We used seven latitudinally arrayed transects to quantify the contributions of climate, geography, and landscape features to broad patterns of genetic structure across the hybrid zone of Populus trichocarpa and P. balsamifera and evaluated the demographic context of hybridization over time. We found genetic structure differed among the seven transects. While ancestry was structured by climate, landscape features influenced gene flow dynamics. Demographic models indicated a secondary contact event may have influenced contemporary hybrid zone formation with the origin of a putative hybrid lineage that inhabits regions with higher aridity than either of the ancestral groups. Phylogenetic relationships based on chloroplast genomes support the origin of this hybrid lineage inferred from demographic models based on nuclear data. Our results point towards the importance of climate and landscape patterns in structuring the contact zones between P. trichocarpa and P. balsamifera and emphasize the value whole genome sequencing can have to advancing our understanding of how neutral processes influence divergence across space and time.

evolutionary biology↗

bioRxiv2023

Novel genomic offset metrics account for local adaptation in climate suitability forecasts and inform assisted migration

Local adaptation is increasingly being integrated into macroecological models, offering an evolutionary perspective that has been largely missing from climate change biogeography. Genomic offsets, which quantify the disruption of existing genotype-environment associations under environmental change, are an informative landscape genomic tool that allows for the incorporation of intra-specific adaptive differentiation into forecasts of climate suitability and thus management planning. Gradient forest (GF), a method originally developed to model community turnover along environmental gradients, is now the most commonly used approach in genomic offset estimation. However, major hurdles in the application of GF-derived offsets are (1) an inability to interpret the absolute magnitude of genomic offsets in a biologically meaningful way and (2) uncertainty in how genomic offsets compare to established species-level approaches like Ecological Niche Models (ENMs). We used both ENMs and novel, genomic offset metrics derived from GF modeling of genomic variation along climatic gradients to assess the climate change vulnerability of red spruce (Picea rubens), a cool-temperate tree species endemic to eastern North America. We show how genomic offsets can be standardized relative to contemporary genomic variation across the landscape to better represent their biological significance and facilitate comparisons among studies. In three common gardens, we found a significant negative relationship between standardized genomic offsets and red spruce growth and higher explanatory power for standardized offsets than (raw) climate transfer distances. We also derived new threshold-based metrics that we term Donor and Recipient Importance and which quantify transferability of propagules between donor and recipient localities while minimizing disruption of genotype-environment associations. This approach leverages landscape genomic information to account for local adaptation when predicting climate suitability. ENMs and our novel genomic offset metrics largely agreed in forecasting drastic northward range shifts. Combining several offset-based metrics, we show that the projected northward shift of suitable climate mainly applies to populations located in the center and northern parts of the current range, whereas southern populations might be able to persist in situ owing to specific local climate adaptations. The novel metrics thus yield refined, region-specific prognoses for local persistence and show how management could be improved by considering assisted migration.

ecology↗

bioRxiv2021

Seeing the Forest for the trees: Assessing genetic offset predictions with Gradient Forest

Gradient Forest (GF) is increasingly being used to forecast climate change impacts, but remains mostly untested for this purpose. We explore its robustness to assumption violations, and relationship to measures of fitness, using SLiM simulations with explicit genome architecture and a spatial metapopulation. We evaluate measures of GF offset in: (1) a neutral model with no environmental adaptation; (2) a monogenic "population genetic" model with a single environmentally adapted locus; and (3) a polygenic "quantitative genetic" model with two adaptive traits, each adapting to a different environment. Although we found GF Offset to be broadly correlated with fitness offsets under both single locus and polygenic architectures. It could also be confounded by neutral demography, genomic architecture, and the nature of the adaptive environment. GF Offset is a promising tool, but it is important to understand its limitations and underlying assumptions, especially when used in the context of forecasting maladaptation.

evolutionary biology↗

bioRxiv2021

Adipocyte-specific modulation of KLF14 expression in mice leads to sex-dependent impacts in adiposity and lipid metabolism

Genome-wide association studies identified single nucleotide polymorphisms on chromosome 7 upstream of KLF14 to be associated with metabolic syndrome traits and increased risk for Type 2 Diabetes (T2D). The associations were more significant in women than in men. The risk allele carriers expressed lower levels of the transcription factor KLF14 in adipose tissues than non-risk allele carriers. To investigate how adipocyte KLF14 regulates metabolic traits in a sex-dependent manner, we characterized high-fat diet fed male and female mice with adipocyte-specific Klf14 deletion or overexpression. Klf14 deletion resulted in increased fat mass in female mice and decreased fat mass in male mice. Female Klf14-deficient mice had overall smaller adipocytes in subcutaneous fat depots but larger adipocytes in parametrial depots, indicating a shift in lipid storage from subcutaneous to visceral fat depots. They had reduced metabolic rates and increased respiratory exchange ratios consistent with increased utilization of carbohydrates as an energy source. Fasting and isoproterenol-induced adipocyte lipolysis was defective in female Klf14-deficient mice and concomitantly adipocyte triglycerides lipase mRNA levels were downregulated. Female Klf14-deficient mice cleared blood triglyceride and NEFA less efficiently than wild type. Finally, adipocyte-specific overexpression of Klf14 resulted in lower total body fat in female but not male mice. Taken together, consistent with human studies, adipocyte KLF14 deficiency in female but not in male mice causes increased adiposity and redistribution of lipid storage from subcutaneous to visceral adipose tissues. Increasing KLF14 abundance in adipocytes of females with obesity and T2D may provide a novel treatment option to alleviate metabolic abnormalities.

physiology↗

bioRxiv2020

Hybrid origin of Populus tomentosa Carr. identified through genome sequencing and phylogenomic analysis

Populus tomentosa is widely distributed and cultivated in the Northern and Central China, where it is of great economic and ecological importance. However, the origin of P. tomentosa remains controversial. Here, we used a PacBio+Hi-C+Illumina strategy to sequence and assemble its 740.2 Mb (2n) genome. The assembly accounts for greater than 92.1% of the 800-megabase genome, comprises 38 chromosomes, and contains 59,124 annotated protein-coding genes. Phylogenomic analyses elucidated dynamic genome evolution events among its closely related white poplars, and revealed that tomentosa is comprised of two subgenomes, which we deomonstrate is likely to have resulted from hybridization between Populus adenopoda as the female, and Populus alba var. pyramidalis as the male, around 3.93 Mya. We also detected structural variations and allele-indels across genome. Our study presents a high quality and well assembled genome, unveils the origin of the widely distributed and planted P. tomentosa, and provides a powerful resource for comparative plant biology, breeding, and biotechnology.

genomics↗

bioRxiv2020

Future climate change promotes novel gene-climate associations in balsam poplar (Populus balsamifera L.), a forest tree species

A central challenge to predicting climate change effects on biodiversity is integrating information on intraspecific variation, specifically population-level local adaptation to climate. Assessing how climate change could disrupt local adaptation to climate can provide a new way of understanding population risk and vulnerability to climate change. For the wide-ranging boreal tree species, balsam poplar (Populus balsamifera L.), we used models of existing population-level genetic differentiation to estimate three key components of populations vulnerability to climate change: (1) predicted shifts in genetic composition with and without migration, (2) the potential for future novel gene-climate associations, and (3) the distance populations would need to migrate to minimize future maladaptation. When assessed across the range of balsam poplar, these three metrics suggest that vulnerability to climate change is greatest in the eastern portion of balsam poplars range, where future maladaptation peaked, migration distances to sites that minimized maladaptation were greatest, and the emergence of novel gene-climate associations were highest. Our results further suggest greater maladaptation to climate when migration distances were limited - consistent with the possibility of migration to lessen maladaptation to future climate. Our work provides a comprehensive evaluation of populations vulnerability to climate change by simultaneously assessing population maladaptation to future climate and the distances populations would need to migrate to minimize maladaptation, in a way that goes beyond species-level bioclimatic modelling. In doing so, our work helps advance towards the long-held goal of incorporating genomic information in models of species responses to climate change.

ecology↗

bioRxiv2019

Climatic niche predicts the landscape structure of locally adaptive standing genetic variation

Within a species range, intraspecific diversity in the form of adaptive standing genetic variation (SGV) may be non-randomly clustered into different geographic regions, reflecting the combined effects of historical range movements and spatially-varying natural selection. As a consequence of a patchy distribution of adaptive SGV, populations in different parts of the range are likely to vary in their capacity to respond to changing selection pressures, especially long-lived sessile organisms like forest trees. However, the spatial distribution of adaptive SGV across the landscape is rarely considered when predicting species responses to environmental change. Here, we use a landscape genomics approach to estimate the distribution of adaptive SGV along spatial gradients reflecting the expansion history and contemporary climatic niche of balsam poplar, Populus balsamifera (Salicaceae), a widely distributed forest tree with a transcontinental distribution in North America. By scanning the genome for signatures of spatially varying local adaptation, we estimated how adaptive SGV has been shaped by geographic distance from the rear range edge (expansion history) versus proximity to the current center of the climatic niche (environmental selection). We found that adaptive SGV was strongly structured by the current climatic niche, with surprisingly little importance attributable to historical effects such as migration out of southern refugia. As expected, the effect of the climatic niche on SGV was strong for genes whose expression is responsive to abiotic stress (drought), although genes upregulated under biotic (wounding) stress also contained SGV that followed climatic and latitudinal gradients. The latter result could reflect parallel selection pressures, or co-regulation of functional pathways involved in both abiotic and biotic stress responses. Our study in balsam poplar suggests that clustering of locally adaptive SGV within ranges primarily reflects spatial proximity within the contemporary climatic niche - an important consideration for the design of effective strategies for biodiversity conservation and avoidance of maladaptation under climate change.

evolutionary biology↗

bioRxiv2019

Trade-offs and selection conflicts in hybrid poplars indicate the stomatal ratio as an important trait regulating disease resistance.

Organisms are constantly challenged by pathogens and pests which can drive the evolution of growth-defense strategies. Plant stomata are essential for gas-exchange during photosynthesis and conceptually lie at the intersection of the physiological demands of growth and exposure to foliar fungal. Generations of natural selection for locally adapted growth-defense strategies can eliminate variation between traits, potentially masking trade-offs and selection conflicts that may have existed in the past. Hybrid populations offer a unique opportunity to reset the clock on selection and to study potentially maladaptive trait variation before selection removes it. We study the interactions of growth, stomatal, ecopysiological, and disease resistance traits in Poplars (Populus) after infection by the leaf rust Melampsora medusae. Phenotypes were measured in a common garden and genotyped at 227K SNPs. We isolate the effects of hybridization on trait variance, discover correlations between stomatal, ecophysiology and disease resistance, examine trade-offs and selection conflicts, and explore the evolution of growth-defense strategies potentially mediated by selection for stomatal traits on the upper leaf surface. These results suggest an important role for stomata in determining growth-defense strategies in organisms susceptible to foliar pathogens, and reinforces the contribution of hybridization studies towards our understanding of trait evolution.

evolutionary biology↗

bioRxiv2018

StomataCounter: a deep learning method applied to automatic stomatal identification and counting

O_LIStomata fulfill an important physiological role and are often phenotyped by researchers in many fields. Currently, no fully automated method exists to perform this task. Researchers typically rely on manual counts of stomata, which is an error-prone method and difficult to reproduce.\nC_LIO_LIWe introduce StomataCounter, an automated stomata counting system using a deep convolutional neural network to identify pores in a variety of different microscopic images. We used a human-in-the-loop approach to train and refine a neural network on a large variety of microscopic images, which helps us achieve robust detection among a number of datasets.\nC_LIO_LIOur network achieves 98.1% identification accuracy on Ginkgo SEM micrographs, and 94.2% transfer accuracy when tested on untrained species.\nC_LIO_LITo facilitate adoption of the method, we make a web tool available under http://www.stomata.science/\nC_LI

plant biology↗