bioRxiv Science⌕ Search

Biology subjects

Raghavan, S.

Publications and source records attributed to Raghavan, S..

At least 19 recordsLinked to original sources

Single-cell perturbation prediction near experimental reproducibility with GENESIS

Single-cell perturbation atlases now measure cellular responses across millions of cells, but the number of possible combinations of biological contexts, perturbations, doses and other experimental variables make exhaustive measurements infeasible. Here, we present GENESIS (Generative ENErgy-based Single-cell Intervention Simulator), a generative framework that predicts single-cell response distributions directly from the covariates defining an experimental condition. GENESIS uses a lightweight neural network trained with the energy score, a strictly proper scoring rule for distributions. We introduce an experiment-calibrated evaluation framework in which prediction error is interpreted relative to the reproducibility of repeated measurements of the same condition. Across the Tahoe-100M small-molecule atlas and a large PBMC cytokine atlas, GENESIS significantly outperforms existing generative models and statistical baselines and approaches experimental reproducibility on independently repeated conditions. Importantly, GENESIS remains accurate when trained on only a fraction of the available experimental conditions or cells, and generated profiles recover experimentally observed context-dependent transcriptional programs. At comparable training-cell budgets, GENESIS achieves more accurate predictions when measurements span more experimental conditions rather than profiling fewer conditions more deeply. Together, these findings suggest a complementary strategy for perturbation studies: broader, lower-depth measurements can expand experimental coverage, while GENESIS augments sparsely sampled populations and predicts responses in unmeasured conditions.

bioinformatics↗

WHAT IS NORMAL? MULTIMODAL CHARACTERIZATION OF NON-DISEASED PEDIATRIC DUODENAL BIOPSIES USING MACHINE LEARNING IMAGE ANALYSIS AND TRANSCRIPTOMICS

Pediatric endoscopy is performed only when clinically indicated, limiting access to healthy duodenal tissue. Biopsies with duodenal no pathologic abnormality (NPA) are often used as controls despite the presence of symptoms or inflammatory disease found elsewhere in the gastrointestinal (GI) tract. We characterized pediatric duodenal NPA tissue across clinical, histologic, cellular, and transcriptomic domains. Methods Archival duodenal NPA biopsies were obtained with clinical metadata and hematoxylin-and-eosin whole-slide images (WSIs). Duodenal mRNA-seq data were analyzed from a subset of patients with duodenal NPA. Clinical metadata and WSIs underwent machine-learning analysis, cell populations were quantified from WSIs, and RNA-seq data underwent differential expression and pathway-enrichment analyses. Results The primary cohort included 195 patients with duodenal NPA. Comparisons between patients with non-duodenal GI disease and those with no GI disease showed differences in inflammatory biomarkers and follow-up utilization. Unsupervised clinical clustering identified three clusters with partial enrichment for IBD with colonic inflammation and Eosinophilic Esophagitis (EoE) with esophageal inflammation. Supervised clinical classification showed modest discrimination. WSI clustering showed limited disease-status discrimination, and cell quantification showed no significant group differences. In the separate RNA-seq cohort of 43 patients, differential-expression and pathway-enrichment analyses identified transcriptional and pathway-level differences between disease-status groups. Conclusions This multi-level characterization indicates that pediatric duodenal NPA tissue should not be treated as a uniform control category. Clinical metadata and transcriptomics revealed clinical and molecular heterogeneity, while histologic and cell analyses showed limited disease-status separation, supporting a refined definition of control tissue.

physiology↗

eSIG-Net: Accurate prediction of single-mutation induced perturbations on protein interactions using a language model

Most proteins exert their functions in complex with other interactors. Single mutations can exhibit a profound impact on perturbing protein interactions, leading to human disease. However, predicting the effect of single mutations on protein interactions remains a major computational challenge. Deep learning, particularly protein language models or transformers, has become an effective tool in bioinformatics for protein structure prediction. However, the functional divergence of mutations makes it difficult to predict their interaction perturbation profiles. To address this fundamental challenge, we present eSIG-Net (edgetic mutation Sequence-based Interaction Grammar Network), a novel sequence-based "Interaction Language Model" for predicting protein interaction alterations caused by single mutations. eSIG-Net combines various protein sequence embeddings, introduces a mutation-encoding module with syntax and evolutionary insights, and employs contrastive learning to evaluate mutation-induced interaction changes. eSIG-Net significantly outperforms current state-of-the-art sequence-based and structure-based prediction methods at predicting mutational impact on protein interactions. We highlight examples where eSIG-Net nominates causal variants with high confidence and elucidates their functional role under relevant biological contexts. Together, eSIG-Net is a first-in-kind "interaction language model" that can accurately predict interaction-specific rewiring by single mutations with only sequence information, and exhibits generalizability across biological contexts.

bioinformatics↗

Diffusion MRI based biomarkers reveal a Prolonged Pre Lesional Phase of Cerebral Small Vessel Disease

BackgroundWhite matter hyperintensities (WMH) are widely used to assess cerebral small vessel disease (SVD) but reflect late-stage injury. Diffusion MRI based biomarkers have been proposed to capture earlier SVD-related microstructural damage but their temporal progression relative to WMH and the risk factors associated with this progression have not been explored. MethodsWe analyzed longitudinal neuroimaging data from 2,047 participants from a population-based cohort study (aged 49-101 years, 47% female). Using multi-output nonlinear mixed-effects models, we characterized the temporal progression of WMH and four diffusion MRI based biomarkers: fractional anisotropy of the genu of the corpus callosum (Genu-FA), peak width of skeletonized mean diffusivity (PSMD), free water (FW), and Arteriolosclerosis-score (ARTS). Models incorporated participant-specific time shifts, correlations between biomarkers, and effects of risk factors (sex, education, APOE {varepsilon}4 status, and cardiometabolic conditions). ResultsARTS, Genu-FA, FW, and PSMD became abnormal in 50% of the study population 16, 12, 10, and 7 years before WMH, respectively. Global markers (ARTS, FW, PSMD, WMH) were correlated, indicating shared substrates of widespread white matter injury. Genu-FA, a vascular risk microstructural injury biomarker, was weakly coupled with WMH and had an earlier but more linear worsening across adulthood. Cardiometabolic conditions predicted earlier worsening of all biomarkers. Females showed earlier WMH, Genu-FA, and ARTS abnormalities whereas males exhibited earlier PSMD and FW abnormalities. ConclusionsDiffusion MRI based biomarkers capture microstructural injury at least a decade before appearance of WMH, revealing a prolonged phase of early SVD and highlighting their potential for SVD prevention.

neuroscience↗

Beyond alignment: synergistic integration is required for multimodal cell foundation models

The vision of a "virtual cell"--a computational model that simulates biological function across modalities and scales--has become a defining goal in computational biology. While powerful unimodal foundation models exist, the lack of large-scale paired data prohibits the joint training of multimodal approaches. This scarcity favors compositional foundation models (CFMs): architectures that fuse frozen unimodal experts via a learned interface. However, it remains unclear when this multimodal fusion adds task-relevant information beyond the strongest unimodal representation and when it merely aggregates redundant signal. Here, we introduce the Synergistic Information Score (SIS), a metric grounded in partial information decomposition (PID), that quantifies the information gain achievable only through cross-modal interactions. Extending theoretical results from self-supervised learning, we show that standard alignment-based fusion objectives on frozen encoders inherently collapse to detecting linear redundancies, limiting their ability to capture nonlinear synergistic states. This distinction is directly relevant for tasks aiming to link tissue morphology and gene expression. Benchmarking ten fusion methods on spatial transcriptomics datasets, we use SIS to demonstrate that tasks dominated by linear redundancies are sufficiently served by unimodal baselines, whereas complex niche definitions benefit from synergy-aware integration objectives that enable cross-modal interactions beyond linear alignment. Finally, we perform a scaling analysis which highlights that fine-tuning a dominant unimodal expert is the most sample-efficient path for standard tasks, suggesting that the benefits of multimodal frameworks only emerge when tasks depend on information distributed across modalities. Together, these results establish that building towards a virtual cell will require a fundamental shift from alignment objectives that emphasize shared structure to synergy-maximizing integration that preserves and exploits complementary cross-modal signal.

bioinformatics↗

The impact of patient biology on racial disparities in breast cancer outcome

Hormone receptor positive (HR+) breast cancer is the most common subtype of breast cancer diagnosed globally. Despite effective targeted therapies, HR+ breast cancer remains a leading cause of cancer-related death in women. Long-standing epidemiological research identifies significantly worse outcomes for Black women diagnosed with HR+ breast cancer relative to White women. While structural factors such as access to healthcare and education level contribute to this outcome disparity, it persists even in analyses where these factors are controlled. In-depth analyses of the somatic molecular biology that may underlie these outcome disparities are hampered by a lack of datasets that represent Black patient populations. Here, we generate a HR+ breast cancer patient transcriptomic dataset that overrepresents Black women and controls for access to healthcare and education level. We find that signatures relating to the tumor microenvironment, i.e. collagen deposition and prognostically unfavorable T-cell landscapes are enriched in HR+ tumors from Black women. Importantly, we find, using experimental model systems in vitro and in vivo, that race-aligned collagen deposition patterns are at least partially attributable to tumor cell-intrinsic signaling and critical for Black breast cancer metastasis. We also find that unfavorable T-cell signatures in HR+ tumors from Black women, which have previously been attributed to race and ancestry, are more strongly poverty-aligned. Using multiple independent datasets, we identify STAT4 as a potential master regulator of this poverty-associated tumor immune signature. Together, these findings provide new evidence that somatic molecular biology of breast cancer patients can be modified by multiple structural factors such as self-identified race and poverty burden to promote poor patient outcomes. Integrating an understanding of structural factors into molecular cancer research is critical for implementing truly personalized, and maximally effective, oncology systems.

cancer biology↗

Adaptive resampling for improved machine learning in imbalanced single-cell datasets

While machine learning models trained on single-cell transcriptomics data have shown great promise in providing biological insights, existing tools struggle to effectively model underrepresented and out-of-distribution cellular features or states. We present a generalizable Adaptive Resampling (AR) approach that addresses these limitations and enhances single-cell representation learning by resampling data based on its learned latent structure in an online, adaptive manner concurrent with model training. Experiments on gene expression reconstruction, cell type classification, and perturbation response prediction tasks demonstrate that the proposed AR training approach leads to significantly improved downstream performance across datasets and metrics. Additionally, it enhances the quality of learned cellular embeddings compared to standard training methods. Our results suggest that AR may serve as a valuable technique for improving representation learning and predictive performance in single-cell transcriptomic models.

bioinformatics↗

Deep learning-enabled scaffolding of spatial arrays of PfCSP epitopes

Malaria is a leading cause of disease in developing countries. The licensed malaria vaccine RTS,S/AS01 confers partial protection in part due to the elicitation of circumsporozoite protein (CSP) antibodies, of which those to the CSP repeat and junctional regions offer the most potent protection. Anti-repeat region antibodies, including the protective antibody L9, frequently develop mutations that promote inter-Fab contacts when bound to CSP in "spiral" quaternary structures. As a first step toward the design of immunogens that elicit L9-like antibodies, we utilized generative deep learning models to design epitope-scaffolds that incorporated up to three junctional repeat epitopes with structural conformations and relative spatial orientations matching those of the multivalent complex of CSP bound to three copies of L9. Affinity and structural studies demonstrated accurate scaffolding of two epitopes with the intended relative orientation, and less accurate positioning of the third epitope. This study demonstrates proof of principle for design of multi-epitope scaffolds with pre-determined relative epitope spatial positioning. The study also represents an initial step toward development of multi-epitope immunogens to elicit antibodies that utilize homotypic interactions to bind pathogen in multivalent clusters.

immunology↗

First-trimester exposure to anti-cytomegalovirus medications: a study of the effects of valaciclovir, letermovir and maribavir on early placental development

Congenital cytomegalovirus (CMV) infection is the leading preventable cause of childhood disability, including sensorineural hearing loss and cerebral palsy in high-income countries. Early maternal treatment with valaciclovir has been shown to reduce fetal infection. However, newer, more potent anti-CMV medications such as letermovir and maribavir are not routinely used in pregnancy due to limited safety data. This study aimed to assess the effect of aciclovir (the active metabolite of valaciclovir), letermovir, and maribavir on cell viability, functionality, and key cell signalling pathways in first-trimester human placental tissue. First-trimester placental tissue was obtained from individuals undergoing surgical abortion for psychosocial indications at 9-13 weeks of gestation. The effect of anti-CMV medications on primary cytotrophoblast cell survival was measured using a standard cell viability assay. The effects of anti-CMV medication exposure on Wnt and epithelial-to-mesenchymal transition (EMT) signalling pathways were evaluated in placental explant cultures. Their impact on cellular proliferation and migration was assessed using placental outgrowth cultures. Exposure to physiological or supraphysiological levels of aciclovir, letermovir, or maribavir for 48 hours did not significantly alter cytotrophoblast cell viability compared to vehicle-treated controls. Aciclovir did not significantly impact Wnt and EMT signalling gene expression in first-trimester placental explants; however, letermovir and maribavir induced significant gene dysregulation. None of the three anti-CMV medications altered first-trimester trophoblast proliferation or migration. These results provide reassuring data supporting the safety of maternal valaciclovir therapy in the first trimester. They may also inform the selection of newer anti-CMV medications for future clinical trials for use in pregnancy.

developmental biology↗

Amniotic fluid extracellular vesicle properties evolve with gestational age and reflect fetal development

Amniotic fluid (AF) is a valuable source of extracellular vesicles (EVs) derived from the fetoplacental unit. Preclinical and clinical studies have highlighted promising applications of AF-EVs and their role in cellular communication, yet our understanding of AF-EV physiology is limited. This study aimed to examine the physiological importance of AF-EVs in fetal development from the second trimester to term gestation. We obtained AF samples from routine second-trimester amniocentesis and prelabour Caesarean section at term. We isolated EVs using a combination of differential centrifugation, filtration, and ultracentrifugation and characterised them using nanoparticle tracking analysis, cryoelectron microscopy, and Western blotting. The differential EV proteome was analysed using label-free proteomics. We assessed the second trimester and term AF-EV properties through an enrichment analysis. The EV size and protein enrichment difference revealed a gestational-age-dependent variation in the predominant EV subtype. Second-trimester-derived EVs were enriched in ectosomes, while term EVs contained a significant proportion of exosomes. We identified several morphologies of AF-EVs, including unilamellar, multilamellar, multicompartmental and granular-centred EVs, across gestations. Proteomics analysis of AF-EVs identified 4137 proteins with high confidence, of which 1099 exhibited significant differential expression between the two groups. Second-trimester-enriched AF-EV proteins represented molecule assembly processes, metabolism and organogenesis. At term, AF-EV proteins corresponded to impending newborn functions such as immunity and digestion. In conclusion, we provide compelling evidence that EV biogenesis and secretion in the fetoplacental unit undergo significant alterations across gestation, revealing a complex and dynamic physiology and intercellular communication that adapts to the needs of the developing fetus. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=126 SRC="FIGDIR/small/649052v1_ufig1.gif" ALT="Figure 1"> View larger version (65K): org.highwire.dtl.DTLVardef@3358c4org.highwire.dtl.DTLVardef@108ec96org.highwire.dtl.DTLVardef@e49b91org.highwire.dtl.DTLVardef@a1888b_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical abstractC_FLOATNO This figure summarises the studys main findings, including the shift in the predominant EV subtype, the different organs and biofluids represented by the enriched proteins at each gestation, and the main biological pathways. C_FIG

developmental biology↗

Hierarchical cross-entropy loss improves atlas-scale single-cell annotation models

Accurately annotating cell types is essential for extracting biological insight from single-cell RNA-seq data. Although cell types are naturally organized into hierarchical ontologies, most computational models do not explicitly incorporate this structure into their training objectives. We introduce a hierarchical cross-entropy loss that aligns model objectives with biological structure. Applied to architectures ranging from linear models to transformers, this simple modification significantly improves out-of-distribution performance (12-15%) without added computational cost.

cell biology↗

Synthetic derivatives of vinpocetine as antiproliferative agents

Vincamine is an indole alkaloid initially isolated from plants of the Vinca genus and has previously been demonstrated to have antioxidant, hypoglycemic, and hypolipidemic activities. Vinpocetine, a synthetic derivative of vincamine with an enhanced pharmacological profile, has demonstrated promising antiproliferative properties. While previously reported vinpocetine derivatives have undergone extensive investigation for their pharmacological properties, the role of the E-ring ethyl ester in the anticancer properties of compounds with this scaffold has not yet been fully described. Here, we report the antiproliferative activity of two vinpocetine analogs with modifications at the E-ring. MTT assays revealed that reduction of the ethyl ester to an alcohol exhibited strong dose-dependent antiproliferative activity across five mammalian cell lines, but did not induce significant markers of apoptosis or necrotic death as determined by FITC/Annexin V and cell cycle flow cytometry, respectively. We further observe that vinpocetine and both analogs exhibit dose-dependent modulation of a TCF/LEF reporter cell, which appears to be decoupled from trends in antiproliferative activity Altogether, this work demonstrates the potential for E-ring modifications of vinpocetine as anticancer agents.

cancer biology↗

Consequences of training data composition for deep learning models in single-cell biology

Foundation models for single-cell transcriptomics have the potential to augment (or replace) purpose-built tools for a variety of common analyses, especially when data are sparse. Recent work with large language models has shown that training data composition greatly shapes performance; however, to date, single-cell foundation models have ignored this aspect, opting instead to train on the largest possible corpus. We systematically investigate the consequences of training dataset composition on the behavior of deep learning models of single-cell transcriptomics, focusing on human hematopoiesis as a tractable model system and including cells from adult and developing tissues, disease states, and perturbation atlases. We find that (1) these models generalize poorly to unseen cell types, (2) adding malignant cells to a healthy cell training corpus does not necessarily improve modeling of unseen malignant cells, and (3) including an embryonic stem cell differentiation atlas during training improves performance on out-of-distribution tasks. Our results emphasize the importance of diverse training data and suggest strategies to optimize future single-cell foundation models.

genomics↗

Evaluating the role of pre-training dataset size and diversity on single-cell foundation model performance

The success of transformer-based foundation models on natural language and images has motivated their use in single-cell biology. Single-cell foundation models have been trained on increasingly larger transcriptomic datasets, scaling from initial studies with 1 million cells to newer atlases with over 100 million cells. This study investigates the role of pre-training dataset size and diversity on the performance of single-cell foundation models on both zero-shot and fine-tuned tasks. Using a large corpus of 22.2 million cells, we pre-train a total of 400 models, which we evaluate by conducting 6,400 experiments. Our results show that current methods tend to plateau in performance with pre-training datasets that are only a fraction of the size of current training corpora.

genomics↗

Mutation and cell state compatibility is required and targetable in Ph+ acute lymphoblastic leukemia minimal residual disease

Efforts to cure BCR::ABL1 B cell acute lymphoblastic leukemia (Ph+ ALL) solely through inhibition of ABL1 kinase activity have thus far been insufficient despite the availability of tyrosine kinase inhibitors (TKIs) with broad activity against resistance mutants. The mechanisms that drive persistence within minimal residual disease (MRD) remain poorly understood and therefore untargeted. Utilizing 13 patient-derived xenograft (PDX) models and clinical trial specimens of Ph+ ALL, we examined how genetic and transcriptional features co-evolve to drive progression during prolonged TKI response. Our work reveals a landscape of cooperative mutational and transcriptional escape mechanisms that differ from those causing resistance to first generation TKIs. By analyzing MRD during remission, we show that the same resistance mutation can either increase or decrease cellular fitness depending on transcriptional state. We further demonstrate that directly targeting transcriptional state-associated vulnerabilities at MRD can overcome BCR::ABL1 independence, suggesting a new paradigm for rationally eradicating MRD prior to relapse. Finally, we illustrate how cell mass measurements of leukemia cells can be used to rapidly monitor dominant transcriptional features of Ph+ ALL to help rationally guide therapeutic selection from low-input samples. HIGHLIGHTSO_LIRelapse after remission on TKI can harbor mutations in ABL1, RAS, or neither C_LIO_LIMutations and development-like cell state dictate fitness in residual disease C_LIO_LICo-targeting cell state and ABL1 markedly reduces MRD C_LIO_LIBiophysical measurements provide an integrative, rapid measurement of cell state C_LI

cancer biology↗

Oncogenic KRAS Mutations Confer a Unique Mechanotransduction Response to Peristalsis in Colorectal Cancer Cells

Colorectal cancer (CRC) tumors start as precancerous polyps on the inner lining of the colon or rectum, where they are exposed to the mechanics of colonic peristalsis. Our previous work leveraged a custom-built peristalsis bioreactor to demonstrate that colonic peristalsis led to cancer stem cell enrichment in colorectal cancer cells. However, this malignant mechanotransductive response was confined to select CRC lines that harbored an oncogenic mutation in the KRAS gene. In this work, therefore, we explored the involvement of activating KRAS mutations on peristalsis-associated mechanotransduction in CRC. Peristalsis enriched the cancer stem cell marker LGR5 in KRAS mutant (G13D, etc.) lines, in a Wnt-independent manner. Conversely, LGR5 enrichment in wild type KRAS lines exposed to peristalsis were minimal. LGR5 enrichment downstream of peristalsis translated to increased tumorigenicity in vivo in KRAS mutant vs. wild type lines. Differences in mechanotransduction response was additionally apparent via unbiased gene set enrichment analysis, where many unique pathways were enriched in wild type vs. mutant lines, in response to peristalsis. Interestingly, peristalsis also triggered {beta}-catenin nuclear localization independent of Wnt, particularly in KRAS mutant lines. The central involvement of KRAS in the mechanotransductive responses was validated via gain and loss of function strategies. {beta}-catenin activation and LGR5 enrichment downstream of peristalsis converged to the activation of the MEK/ERK kinase cascade, that remains active in cells that harbor oncogenic KRAS mutations. Taken together, our results demonstrated that oncogenic KRAS mutations conferred a unique peristalsis-associated mechanotransduction response to colorectal cancer cells, resulting in cancer stem cell enrichment and increased tumorigenicity. These mechanosensory connections can be leveraged in improving the sensitivity of emerging therapies that target oncogenic KRAS.

bioengineering↗

A knockoff calibration method to avoid over-clustering in single-cell RNA-sequencing

Standard single-cell RNA-sequencing (scRNA-seq) pipelines nearly always include unsupervised clustering as a key step in identifying biologically distinct cell types. A follow-up step in these pipelines is to test for differential expression between the identified clusters. When algorithms over-cluster, downstream analyses will produce inflated P -values resulting in increased false discoveries. In this work, we present callback (Calibrated Clustering via Knockoffs): a new method for protecting against over-clustering by controlling for the impact of reusing the same data twice when performing differential expression analysis, commonly known as "double-dipping". Importantly, our approach can be applied to a wide range of clustering algorithms. Using real and simulated data, we show that callback provides state-of-the-art clustering performance and can rapidly analyze large-scale scRNA-seq studies, even on a personal laptop.

bioinformatics↗

Scalable nonparametric clustering with unified marker gene selection for single-cell RNA-seq data

Clustering is commonly used in single-cell RNA-sequencing (scRNA-seq) pipelines to characterize cellular heterogeneity. However, current methods face two main limitations. First, they require user-specified heuristics which add time and complexity to bioinformatic workflows; second, they rely on post-selective differential expression analyses to identify marker genes driving cluster differences, which has been shown to be subject to inflated false discovery rates. We address these challenges by introducing nonparametric clustering of single-cell populations (NCLUSION): an infinite mixture model that leverages Bayesian sparse priors to identify marker genes while simultaneously performing clustering on single-cell expression data. NCLUSION uses a scalable variational inference algorithm to perform these analyses on datasets with up to millions of cells. Through simulations and analyses of publicly available scRNA-seq studies, we demonstrate that NCLUSION (i) matches the performance of other state-of-the-art clustering techniques with significantly reduced runtime and (ii) provides statistically robust and biologically relevant transcriptomic signatures for each of the clusters it identifies. Overall, NCLUSION represents a reliable hypothesis-generating tool for understanding patterns of expression variation present in single-cell populations.

bioinformatics↗