Biology subjects

Ma, E.

Publications and source records attributed to Ma, E..

At least 19 recordsLinked to original sources

bioRxiv2026

Patient-Derived Glioma Models Preserve Tumor Heterogeneity and Identify Stearoyl-CoA Desaturase1 (SCD1) as a Candidate Biomarker for Precision Immunotherapy

Background: Pediatric and adult brain tumors, including glioblastoma, astrocytoma, ependymoma, and medulloblastoma, remain associated with poor prognosis despite advances in surgery, radiation, and chemotherapy. Therapeutic resistance, tumor heterogeneity, and treatment-related toxicity highlight the need for clinically relevant models that enable precision medicine and immunotherapy development. Methods: Freshly dispersed tumors (FDTs), low-passage patient-derived brain tumor (PBT) spheroid lines, and matched patient-derived xenograft (PDX) models were established from patients with primary brain tumors. Models were characterized using single-cell and bulk RNA sequencing, whole-exome sequencing, multiparameter flow cytometry, and immunohistochemistry. PBTs were compared with matched FDTs to evaluate model fidelity. Results: PBT lines were established in approximately 68% of cases and retained key patient-specific genomic alterations, including IDH1, MGMT, TP53, and PTEN, with expression of therapeutically relevant targets, including IL13R2, EGFR, HER2, WNT1, JAK1/2, and NOTCH1-4. Gene expression profiles of PBTs closely correlated with matched FDTs (R = 0.38, P = 0.0038). PBT and PDX models preserved intratumoral heterogeneity and non-clonal populations, enabling identification of therapy-resistant subclones during in vitro selection. Molecular analyses identified Stearoyl-CoA Desaturase1 (SCD1) as an overexpressed biomarker across glioma PBTs and matched patient tumors. Ingenuity Pathway Analysis identified SCD1 as an upstream regulator of EGFR-, TP53-, and CYCS-associated signaling networks implicated in tumor progression and immune suppression. Conclusions: Clinically relevant PBT and matched PDX models recapitulate molecular, transcriptional, and histopathological characteristics of primary brain tumors. These platforms provide tools for biomarker discovery, therapeutic testing, and precision immunotherapy development, while identifying SCD1 as a biomarker and therapeutic target in glioma.

cancer biology↗

bioRxiv2026

Programming T cells for intercellular genome editing

Therapeutic genome editing requires delivery of editing molecules to defined cell types, but targeting specificity and efficiency are currently limited. We hypothesized that properties inherent to immune cells, including tissue infiltration and programmed cell recognition, could be harnessed to engineer a cell-based delivery system. We show here that T cells can both produce and transfer editing machinery to target cells. In response to a programmable ligand, engineered T-lymphoid cells can transfer enzymes using complex spatiotemporal logic and deliver cargo in a cell contact-dependent or -independent manner. We demonstrate feasibility of this approach in primary human T cells, establishing a customizable genetic circuit for macromolecular delivery controlled by intercellular interactions.

bioengineering↗

bioRxiv2026

Multi-Objective Bayesian Optimization for Data-Efficient Bioprocess Development

Process optimization for Chinese hamster ovary (CHO) cell culture remains a challenge in biopharmaceutical development because multiple interacting parameters jointly influence productivity and product quality attributes. Traditional design-of-experiments (DoE) methods, while systematic, become impractically expensive when extended across multiple parameters and clones. To address this challenge, we developed a multi-objective Bayesian Optimization (BO) framework that identifies optimal process conditions efficiently in grouped recommendations, which is well suited for experimental workflows in bioprocess development. The model integrates continuous variables such as pH, DO, temperature, and feed rate with categorical identifiers to enable knowledge transfer across clones and scales, optimizing titer, glycan profile, and charge variants. We validated the framework through in-silico benchmarks on analytic functions, retrospective cross-validation on historical CHO datasets, and forward experimental validation in small-scale bioreactors. Across these tests, our algorithm consistently outperformed Latin Hypercube Sampling (LHS) and Random Search baselines, achieving superior performance under a limited experimental budget. The framework improved titer by up to 37% under single-objective optimization. In the multi-objective setting, it increased titer by 25% while simultaneously reducing overall glycan-profile error by a factor of seven, demonstrating the ability to optimize multiple biologically coupled objectives simultaneously. Through comprehensive in-silico and experimental validation, this study establishes a framework that enables adaptive, AI-guided process development and improves decision-making across multiple objectives, clones, and scales while minimizing experimental runs in process development and optimization workflows.

bioengineering↗

bioRxiv2026

Mena (ENAH) Promotes KRAS-Driven Tumor Growth and Metastatic Progression in Pancreatic Ductal Adenocarcinoma

Metastatic pancreatic ductal adenocarcinoma (PDAC) remains incurable and is projected to become the second leading cause of cancer-related death by 2030. Despite therapeutic advances, median survival remains under one year. Activating KRAS mutations drive the majority of PDAC and underlie their highly aggressive behavior. Although emerging KRAS inhibitors show promise, resistance limits their clinical efficacy, underscoring the need to identify additional regulators of mutant KRAS signaling. We investigated the role of the actin-regulatory protein Mena (ENAH) in KRASG12D-driven PDAC using novel in vitro and orthotopic in vivo models with Mena overexpression and knockdown. Mena overexpression markedly increased primary tumor growth and spontaneous liver metastasis, whereas Mena knockdown delayed tumor onset and reduced metastatic burden. Mechanistically, Mena depletion significantly decreased AKT and ERK activity downstream of KRAS in a SHIP2-mediated manner, indicating that Mena enhances oncogenic signaling required for PDAC progression. These findings reveal Mena as a critical modulator of KRASG12D-driven pancreatic tumor growth and metastasis. By promoting key survival and proliferation pathways, Mena contributes to the aggressive phenotype characteristic of KRAS-mutant PDAC and represents a promising therapeutic target for patients with both locoregional and metastatic disease.

cancer biology↗

bioRxiv2025

Corticolimbic structure-function coupling is sensitive to childhood adversity and buffers adversity-related symptoms during development

Childhood adversity is a potent predictor of mental health problems across the lifespan, and a rich cross-species literature implicates stress-sensitive corticolimbic circuits in adversity-related psychopathology. Structure-function coupling (SFC) is a promising multimodal marker that is sensitive to developmental plasticity. While emerging evidence suggests cortical SFC is sensitive to adversity exposure during early childhood, it is unknown how SFC in stress-sensitive corticolimbic circuits links adversity exposure with mental health across development. We examined associations between adversity exposure, transdiagnostic symptomatology, and both amygdala-cortical and hippocampal-cortical SFC across development in a large sample of youth (N = 607, 39% F). Results revealed that adversity exposure moderated age-related change in amygdala-vmPFC SFC (p = .007), such that youth exposed to higher, but not lower, levels of adversity showed an age-related increase in amygdala-vmPFC SFC. Further, amygdala-vmPFC SFC buffered the effect of adversity on internalizing symptoms (p = .012), such that those youth with higher adversity exposure who had stronger amygdala-vmPFC SFC also displayed lower internalizing symptoms. Separately, higher adversity exposure was associated with lower hippocampal-limbic network SFC (p = .037), which moderated the effect of adversity on internalizing symptoms (p = .010). These findings highlight that structural and functional neurodevelopment of amygdala-vmPFC and hippocampal-limbic network connections may adapt in distinct ways to support mental health following adversity, with implications for risk and resilience against internalizing psychopathology. Significance StatementDelineating how childhood adversity alters neurodevelopment is critical to understanding the origins of adversity-related risk for mental health disorders. Here, we leverage a multimodal marker of the correspondence between brain structure and function to test how corticolimbic circuits are jointly shaped by adversity exposure. Results reveal that the structure-function coupling of amygdala-vmPFC and hippocampal-limbic networks is associated with adversity exposure and differentially moderate risk for internalizing psychopathology. These findings suggest key roles for neural stress regulation and memory circuits in adapting to support optimal functioning following adversity exposure, and highlight the concordance of neural structure and function as an important indicator of individual-level risk and resilience.

neuroscience↗

bioRxiv2025

Comparing Kinetic versus Stoichiometric Priorities in Hybrid Models of CHO Metabolism

Understanding Chinese hamster ovary (CHO) cell metabolism through mathematical models is essential for optimizing culture media and biomanufacturing processes. Current mechanistic models rely primarily on either flux balance analysis (FBA), estimating intracellular fluxes while assuming steady state, or kinetic modeling, capturing dynamic behavior but typically for a limited number of reactions. Dynamic FBA (dFBA) integrates both approaches in a hybrid framework, but challenges remain in integrating the two formats to describe bioprocesses. In this study, we first enhanced an existing dynamic CHO-metabolism model by incorporating 13C-labeled data to refine kinetic expressions and stoichiometric constraints of amino acid pathways, including the asparagine-aspartate network and serine biosynthesis. We next evaluated the impact of prioritizing either stoichiometry, through the pseudo steady state assumption (PSSA), or the kinetic expressions of fluxes. Comparing error and predictive performance for both models for two industrially relevant fed-batch CHO culture conditions involving varying initial concentrations of nutrients and three feed streams, demonstrated that the kinetic-oriented model (KOM) yielded superior predictions for viable cell density (VCD), antibody production, and a range of amino acids and metabolites compared to the stoichiometric oriented model (SOM). Indeed, the KOM was able to predict production-to-consumption shifts of lactate and alanine, fluctuating levels of ammonia based on reversible kinetic expressions, and amino acids like asparagine and the serine-glycine pool. The KOM also provided better predictions for a third case including lactate-supplemented (LS) feed; however, slight parameter adjustments helped to improve model fidelity, likely due to the impact of high lactate on kinetic expressions of antibody (directly) and VCD (indirectly). In summary, our findings demonstrate that hybrid models emphasizing empirical kinetics over strict pseudo-steady-state constraints capture biologically realistic dynamics such as transient shifts for key metabolites like lactate, alanine, and ammonia, and also produce parameters useful across varying conditions, making them a practical and powerful tool for characterizing CHO cell culture performance in the future.

systems biology↗

bioRxiv2025

Directed evolution expands CRISPR-Cas12a genome editing capacity

CRISPR-Cas12a enzymes are versatile RNA-guided genome-editing tools with applications encompassing viral diagnosis, agriculture and human therapeutics. However, their dependence on a 5-TTTV-3 protospacer-adjacent motif (PAM) next to DNA target sequences restricts Cas12as gene targeting capability to only [~]1% of a typical genome. To mitigate this constraint, we used a bacterial-based directed evolution assay combined with rational engineering to identify variants of Lachnospiraceae bacterium Cas12a (LbCas12a) with expanded PAM recognition. The resulting Cas12a variants use a range of non-canonical PAMs while retaining recognition of the canonical 5-TTTV-3 PAM. In particular, biochemical and cell-based assays show that the variant Flex-Cas12a utilizes 5-NYHV-3 PAMs that expand DNA recognition sites to [~]25% of the human genome. With enhanced targeting versatility, Flex-Cas12a unlocks access to previously inaccessible genomic loci, providing new opportunities for both therapeutic and agricultural genome engineering.

biochemistry↗

bioRxiv2024

Targeting endothelial ERG to mitigate vascular regression and neuronal ischemia in retinopathies

Retinopathy of prematurity (ROP) and diabetic retinopathy (DR) are ocular disorders in which a loss of retinal vasculature leads to ischemia followed by a compensatory neovascularization response. In mice, this is modeled using oxygen-induced retinopathy (OIR), whereby neonatal animals are transiently housed under hyperoxic conditions that result in central retina vessel regression and subsequent neovascularization. Using endothelial cell (EC)-specific gene deletion, we found that loss of two ETS-family transcription factors, ERG and FLI1, led to regression of OIR-induced neovascular vessels but failed to improve visual function, suggesting that relevant retinal damage occurs prior to and independently of neovascularization. Turning our attention to the initial stage of OIR, we found that hyperoxia repressed ERG expression in retinal ECs of wild type mice, raising the possibility that oxygen-induced ERG downregulation promotes vessel regression during the initiation of OIR-induced pathology. We therefore developed a murine model of EC-specific ERG overexpression and found it sufficient to prevent hyperoxia-induced vascular regression, neuronal cell death, and neovascularization in the OIR model. Importantly, ERG overexpression also improved visual function in OIR-challenged mice. Moreover, we show that both ERG and FLI1 are downregulated in the retinal vessels of human patients with early stages of DR, suggesting that neovascular disorders of the eye may share common mechanisms underlying pathological retinal capillary regression. Collectively, these data suggest that the regulation of vascular regression by EC-expressed ETS transcription factors may be adapted towards novel therapeutic approaches for the prevention and/or alleviation of ocular neovascular disorders.

pathology↗

bioRxiv2024

Rad52 Acts as an Assembly Chaperone to Form and Stabilize Rad51 Filaments Through a Large C-Terminus 85-Residue Segment

Homologous recombination (HR) is essential for the repair of DNA double-strand breaks and the restart of stalled replication forks. A critical step in HR is the formation of Rad51 nucleofilaments, which perform homology search and strand invasion of a homologous DNA sequence required for repair synthesis. In the yeast Saccharomyces cerevisiae, Rad52 facilitates Rad51 nucleofilament formation by mediating Rad51 loading onto ssDNA and counteracting the dissociation of Rad51 filaments by the DNA translocase Srs2. The molecular basis of these two Rad52 functions remains unclear. Our integrative structural analyses of the Rad51-Rad52 interaction, combining NMR, SAXS, and modeling, reveal that an 85-residue segment of Rad52, conserved in fungi, folds upon binding to a broad surface of a Rad51 monomer. Notably, it includes an FxxA motif conserved in the BRC repeats of BRCA2 and at the Rad51-Rad51 interface. This binding mode was validated through an extensive set of mutations. Using in vivo assays and a functional fluorescent GFP-Rad51 fusion protein, we demonstrated that this entire segment is critical for Rad51 filament formation. These findings highlight how Rad52 functions as an assembly chaperone, preventing Rad51 oligomerization, promoting nucleation of Rad51 nucleofilaments on ssDNA, and protecting Rad51 filaments from destabilization by Srs2.

molecular biology↗

bioRxiv2023

mtx-COBRA: Subcellular localization prediction for bacterial proteins

BackgroundBacteria can have beneficial effects on our health and environment; however, many are responsible for serious infectious diseases, warranting the need for vaccines against such pathogens. Bioinformatic and experimental technologies are crucial for the development of vaccines. The vaccine design pipeline requires identification of bacteria-specific antigens that can be recognized and induce a response by the immune system upon infection. Immune system recognition is influenced by the location of a protein. Methods have been developed to determine the subcellular localization (SCL) of proteins in prokaryotes and eukaryotes. Bioinformatic tools such as PSORTb can be employed to determine SCL of proteins, which would be tedious to perform experimentally. Unfortunately, PSORTb often predicts many proteins as having an "Unknown" SCL, reducing the number of antigens to evaluate as potential vaccine targets. MethodWe present a new pipeline called subCellular lOcalization prediction for BacteRiAl Proteins (mtx-COBRA). mtx-COBRA uses Metas protein language model, Evolutionary Scale Modeling, combined with an Extreme Gradient Boosting machine learning model to identify SCL of bacterial proteins based on amino acid sequence. This pipeline is trained on a curated dataset that combines data from UniProt and the publicly available ePSORTdb dataset. ResultsUsing benchmarking analyses, nested 5-fold cross-validation, and leave-one-pathogen-out methods, followed by testing on the held-out dataset, we show that our pipeline predicts the SCL of bacterial proteins more accurately than PSORTb. Conclusionsmtx-COBRA provides an accessible pipeline with greater efficiency to classify bacterial proteins with currently "Unknown" SCLs than existing bioinformatic and experimental methods.

bioinformatics↗

bioRxiv2022

Innate immune sensing of self-derived double-stranded RNA by RIG-I-MAVS-TNF-α regulates the survival and senescence fate of SARS-2-S syncytia

Patients with pre-existing heart failure are at a particularly high risk of morbidity and mortality resulting from SARS-CoV-2 infection. Direct acute cardiac injury or cytokine storms have been proposed to contribute to depressed cardiac function. However, the pathogenic mechanisms underlying the increased vulnerability to heart failure in SARS-CoV-2 infected patients are still largely unknown. Here, we found that the senescent outcome of SARS-CoV-2 spike protein (SARS-2-S)-induced syncytia exacerbated heart failure progression. We first demonstrated that syncytium formation in cells expressing SARS-2-S delivered by DNA plasmid or LNP-mRNA exhibits a senescence-like phenotype. Extracellular vesicles containing SARS-2-S (S-EVs) also confer a potent ability to form senescent syncytia without denovosynthesis of SARS-2-S. Mechanistically, SARS-2-S syncytia provoke the formation of functional MAVS aggregates, which regulate the senescence fate of SARS-2-S syncytia by TNF . We further demonstrate that senescent SARS-2-S syncytia exhibit shrinked morphology, leading to the activation of WNK1 and impaired cardiac metabolism. In pre-existing heart failure mice, the WNK1 inhibitor WNK463, anti-syncytial drug niclosamide, and senolytic dasatinib protect the heart from exacerbated heart failure triggered by pseudovirus expressing SARS-2-S (SARS-2-Spp). Signs of senescent multinucleated cells are identified in ascending aorta from SARS-CoV-2 omicron variant-infected patient. Our findings thus suggest a potential mechanism for COVID-19-mediated cardiac pathology and recommend the application of WNK1 inhibitor for therapy. Significance StatementIn this paper, we directly linked SARS-2-S-triggered syncytium formation with the ensuing induction of cellular senescence and its pathophysiological contribution to heart failure. We propose that both SARS-2-S expression and SARS-2-S protein internalization were sufficient to induce senescence in nonsenescent ACE2-expressing cells. This is important because of the persistent existence of SARS-2-S or extracellular vesicles containing SARS-2-S during the acute and post-acute stages of SARS-CoV-2 infection in human subjects. In searching for the underlying molecular mechanisms determining syncytial fate, the formation of functional MAVS aggregates dependent on RIG-I was observed at an early stage during fusion and regulated the anti-death to senescence fate of SARS-2-S syncytia through the TNF-TNFR2 axis. We also found impaired cardiac metabolism in SARS-2-S syncytia induced by condensed WNK1. Importantly, SARS-2-Spp-exacerbated heart failure could be largely rescued by WNK1 inhibitor, anti-syncytial drug or senolytic agent. Together, we suggest that rescuing metabolism dysfunction in senescent SARS-2-S syncytia should be taken into consideration in individuals during the acute or post-acute stage of SARS-CoV-2 infection.

cell biology↗

bioRxiv2022

Improved Genome Editing by an Engineered CRISPR-Cas12a

CRISPR-Cas12a is an RNA-guided, programmable genome editing enzyme found within bacterial adaptive immune pathways. Unlike CRISPR-Cas9, Cas12a uses only a single catalytic site to both cleave target double-stranded DNA (dsDNA) (cis-activity) and indiscriminately degrade single-stranded DNA (ssDNA) (trans-activity). To investigate how the relative potency of cis- versus trans-DNase activity affects Cas12a-mediated genome editing, we first used structure-guided engineering to generate variants of Lachnospiraceae bacterium Cas12a (LbCas12a) that selectively disrupt trans-activity. The resulting engineered mutant with the biggest differential between cis- and trans-DNase activity in vitro showed minimal genome editing activity in human cells, motivating a second set of experiments using directed evolution to generate additional mutants with robust genome editing activity. Notably, these engineered and evolved mutants had enhanced ability to induce homology-directed repair (HDR) editing by 2-18-fold depending on the genomic locus. Finally, we found that a site-specific reversion mutation produced improved Cas12a (iCas12a) variants with superior genome editing efficiency at genomic sites that are difficult to edit using wild-type Cas12a. This strategy of coupled rational engineering and directed evolution establishes a pipeline for creating improved genome editing tools by combining structural insights with randomization and selection. The availability of experimental and predicted structures of other CRISPR-Cas enzymes will enable this strategy to be applied to improve the efficacy of other genome editing proteins.

biochemistry↗

bioRxiv2022

PGC-1β maintains mitochondrial metabolism and restrains inflammatory gene expression

Metabolic programming of the innate immune cells known as dendritic cells (DCs) changes in response to different stimuli, influencing their function. While the mechanisms behind increased glycolytic metabolism in response to inflammatory stimuli are well-studied, less is known about the programming of mitochondrial metabolism in DCs. We used lipopolysaccharide (LPS) and interferon-{beta} (IFN-{beta}), which differentially stimulate the use of glycolysis and oxidative phosphorylation (OXPHOS), respectively, to identify factors important for mitochondrial metabolism. We found that the expression of peroxisome proliferator-activated receptor gamma coactivator 1{beta} (PGC-1{beta}), a transcriptional co-activator and known regulator of mitochondrial metabolism, decreases when DCs are activated with LPS, when OXPHOS is diminished, but not with IFN-{beta}, when OXPHOS is maintained. We examined the role of PGC-1{beta} in bioenergetic metabolism of DCs and found that PGC-1{beta} deficiency in DCs indeed impairs mitochondrial respiration. PGC-1{beta}-deficient DCs are more glycolytic compared to controls, likely to compensate for reduced OXPHOS. PGC-1{beta} deficiency also causes decreased capacity for ATP production at steady state and in response to IFN-{beta} treatment. Loss of PGC-1{beta} in DCs leads to increased expression of genes in inflammatory pathways, and reduced expression of genes encoding proteins important for mitochondrial metabolism and function. Collectively, these results demonstrate that PGC-1{beta} is a key positive regulator of mitochondrial metabolism in DCs.

immunology↗

bioRxiv2021

Destabilization of CAR T-cell treatment efficacy in the presence of dexamethasone

Chimeric antigen receptor (CAR) T-cell therapy is potentially an effective targeted immunotherapy for glioblastoma, yet there is presently little known about the efficacy of CAR T-cell treatment when combined with the widely used anti-inflammatory and immunosuppressant glucocorticoid, dexamethasone. Here we present a mathematical model-based analysis of three patient-derived glioblastoma cell lines treated in vitro with CAR T-cells and dexamethasone. Advanced in vitro experimental cell killing assay technologies allow for highly resolved temporal dynamics of tumor cells treated with CAR T-cells and dexamethasone, making this a valuable model system for studying the rich dynamics of nonlinear biological processes with translational applications. We model the system as a nonautonomous, two-species predator-prey interaction of tumor cells and CAR T-cells, with explicit time-dependence in the clearance rate of dexamethasone. Using time as a bifurcation parameter, we show that (1) dexamethasone destabilizes coexistence equilibria between CAR T-cells and tumor cells in a dose-dependent manner and (2) as dexamethasone is cleared from the system, a stable coexistence equilibrium returns in the form of a Hopf bifurcation. With the model fit to experimental data, we demonstrate that high concentrations of dexamethasone antagonizes CAR T-cell efficacy by exhausting, or reducing the activity of CAR T-cells, and by promoting tumor cell growth. Finally, we identify a critical threshold in the ratio of CAR T-cell death to CAR T-cell proliferation rates that predicts eventual treatment success or failure that may be used to guide the dose and timing of CAR T-cell therapy in the presence of dexamethasone in patients. Author summaryBioengineering and gene-editing technologies have paved the way for advance immunotherapies that can target patient-specific tumor cells. One of these therapies, chimeric antigen receptor (CAR) T-cell therapy has recently shown promise in treating glioblastoma, an aggressive brain cancer often with poor patient prognosis. Dexamethasone is a commonly prescribed anti-inflammatory medication due to the health complications of tumor associated swelling in the brain. However, the immunosuppressant effects of dexamethasone on the immunotherapeutic CAR T-cells are not well understood. To address this issue, we use mathematical modeling to study in vitro dynamics of dexamethasone and CAR T-cells in three patient-derived glioblastoma cell lines. We find that in each cell line studied there is a threshold of tolerable dexamethasone concentration. Below this threshold, CAR T-cells are successful at eliminating the cancer cells, while above this threshold, dexamethasone critically inhibits CAR T-cell efficacy. Our modeling suggests that in the presence of high dexamethasone reduced CAR T-cell efficacy, or increased exhaustion, can occur and result in CAR T-cell treatment failure.

cancer biology↗

bioRxiv2021

The homologous recombination complex of the Rad51 paralogs Rad55-Rad57 avoids translesion DNA polymerase recruitment and counterbalances mutagenesis induced by UV radiation

The bypass of DNA lesions that block replicative polymerases during DNA replication relies on DNA damage tolerance pathways. The error-prone translesion synthesis (TLS) pathway depends on specialized DNA polymerases that incorporate nucleotides in front of base lesions, potentially inducing mutagenesis. Two error-free pathways can bypass the lesions: the template switching pathway, which uses the sister chromatid as a template, and the homologous recombination pathway (HR), which also can use the homologous chromosome as template. The balance between error-prone and error-free pathways controls the mutagenesis level. Therefore, it is crucial to precisely characterize factors that influence the pathway choice to better understand genetic stability at replication forks. In yeast, the complex formed by the Rad51 paralogs Rad55 and Rad57 promotes HR and template-switching at stalled replication forks. At DNA double-strand breaks (DSBs), this complex promotes Rad51 filament formation and stability, notably by counteracting the Srs2 anti-recombinase. To explore the role of the Rad55-Rad57 complex in error-free pathways, we monitored the genetic interactions between Rad55-Rad57, the translesion polymerases Pol{zeta} or Pol{eta}, and Srs2 following UV radiation that induces mostly single-strand DNA gaps. We found that the Rad55-Rad57 complex was involved in three ways. First, it protects Rad51 filaments from Srs2, as it does at DSBs. Second, it promotes Rad51 filament stability independently of Srs2. Finally, we observed that UV-induced HR is almost abolished in Rad55-Rad57 deficient cells, and is partially restored upon Pol{zeta} or Pol{eta} depletion. Hence, we propose that the Rad55-Rad57 complex is essential to promote Rad51 filament stability on single-strand DNA gaps, notably to counteract the error-prone TLS polymerases and mutagenesis. Author summaryProcessive and accurate DNA polymerases replicate genomic DNA during the S phase of each cell cycle. DNA base lesions on template DNA block these polymerases and result in an accumulation of single-stranded DNA gaps behind moving replication forks. These gaps are filled-in by error-prone and error-free pathways. In this work, we show that the complex made by the Rad51 paralogs Rad55 and Rad57 is essential for the error-free homologous recombination gap-filling pathway when DNA replication is stalled by UV-induced DNA lesions, but not for DNA double strand break repair. Interestingly, we found that homologous recombination is efficiently outcompeted by error-prone translesion DNA polymerases in Rad55-Rad57-deficient cells. We propose that the Rad55-Rad57 complex is essential for Rad51 filament stability at UV-induced DNA gaps to promote efficient error-free homologous recombination. Furthermore, our study in yeast predicts that inhibitors of error-prone DNA polymerases might selectively target cancer cells in which RAD51 paralogs are mutated.

genetics↗

bioRxiv2021

Rad52 oligomeric N-terminal domain stabilizes Rad51 nucleoprotein filaments and contributes to their protection against Srs2

Homologous recombination (HR) depends on the formation of a nucleoprotein filament of the recombinase Rad51 to scan the genome and invade the homologous sequence used as template for DNA repair synthesis. Therefore, HR is highly accurate and crucial for genome stability. Rad51 filament formation is controlled by positive and negative factors. In Saccharomyces cerevisiae, the mediator protein Rad52 catalyzes Rad51 filament formation and stabilizes them, mostly by counteracting the disruptive activity of the translocase Srs2. Srs2 activity is essential to avoid the formation of toxic Rad51 filaments, as revealed by Srs2-deficient cells. We previously reported that Rad52 SUMOylation or mutations disrupting the Rad52-Rad51 interaction suppress Rad51 filament toxicity because they disengage Rad52 from Rad51 filaments and reduce their stability. Here, we found that mutations in Rad52 N-terminal domain also suppress the DNA damage sensitivity of Srs2-deficient cells. Structural studies showed that these mutations affect the Rad52 oligomeric ring structure. Overall, in vivo and in vitro analyzes of these mutants indicate that Rad52 ring structure is important for protecting Rad51 filaments from Srs2, but can increase Rad51 filament stability and toxicity in Srs2-deficient cells. This stabilization function is distinct from Rad52 mediator and annealing activities.

molecular biology↗

bioRxiv2021

Principled decision-making workflow with hierarchical Bayesian models of high throughput dose-response measurements

We present a case study applying hierarchical Bayesian estimation on high throughput protein melting point data measured across the tree of life. We show that the model is able to impute reasonable melting temperatures even in the face of unreasonably noisy data. Additionally, we demonstrate how to use the variance in melting temperature posterior distribution estimates to enable principled decision-making in common high throughput measurement tasks, and contrast the decision-making workflow against simple maximum-likelihood curve fitting. We conclude with a discussion of the relative merits of each workflow.

molecular biology↗

bioRxiv2021

Antimalarials in mosquitoes overcome Anopheles and Plasmodium resistance to malaria control strategies

The spread of insecticide resistance in Anopheles mosquitoes and drug resistance in Plasmodium parasites is contributing to a global resurgence of malaria, making the generation of control tools that can overcome these issues an urgent public health priority. We recently showed that the transmission of Plasmodium falciparum parasites can be efficiently blocked when exposing Anopheles gambiae females to antimalarials deposited on a treated surface, with no negative consequences on mosquito fitness. Here, we demonstrate this approach can overcome the hurdles of insecticide resistance in mosquitoes and drug resistant in parasites. We show that the transmission-blocking efficacy of mosquito-targeted antimalarials is maintained when field-derived, insecticide resistant Anopheles are exposed to the potent cytochrome b inhibitor atovaquone, demonstrating that this drug escapes insecticide resistance mechanisms that could potentially interfere with its function. Moreover, this approach prevents transmission of field-derived, artemisinin resistant P. falciparum parasites (Kelch13 C580Y mutant), proving that this strategy could be used to prevent the spread of parasite mutations that induce resistance to front-line antimalarials. Atovaquone is also highly effective at limiting parasite development when ingested by mosquitoes in sugar solutions, including in ongoing infections. These data support the use of mosquito-targeted antimalarials as a promising tool to complement and extend the efficacy of current malaria control interventions. Significance StatementEffective control of malaria is hampered by resistance to vector-targeted insecticides and parasite-targeted drugs. This situation is exacerbated by a critical lack of chemical diversity in both interventions and, as such, new interventions are badly needed. Recent laboratory studies have shown that an alternative approach based on treating Anopheles mosquitoes directly with antimalarial compounds can render the vector incapable of transmitting the Plasmodium parasites that cause malaria. While promising, showing that mosquito-targeted antimalarials remain effective against wild parasites and mosquitoes, including drug- and insecticide-resistant populations, respectively, is crucial to the future viability of this approach. In this study, carried out in the US and Burkina Faso, we show that antimalarial exposure is highly effective, even against extremely resistant mosquitoes, and can block transmission of drug-resistant parasites. By combining lab, and field-based studies in this way we have demonstrated that this novel approach can be effective in areas where conventional control measures are no longer as effective.

microbiology↗