Biology subjects

Jain, A.

Publications and source records attributed to Jain, A..

At least 55 records · Page 3Linked to original sources

bioRxiv2025

Development of the Early Childhood Duodenum across Ancestry, Geography and Environment

During early childhood, the proximal small intestinal mucosa plays a central role in growth, metabolism, immune priming, and neuronal development. Yet the cellular architecture and environmental responsiveness of the human small intestinal mucosa during this period remain poorly defined. Here, we generate a comprehensive cellular and spatial map of the duodenum from 87 children aged 6 months to 13 years, representing diverse ancestries and geographic contexts. This atlas integrates single-cell transcriptomic and spatial profiling with data on diet, social drivers of health, and environmental exposures. Using these data, we define mucosal cellular composition and chart its developmental trajectory in early childhood. Comparative analyses of children residing in the United States (US) and Pakistan reveal a differentiated enterocyte subset expressing the aquaglyceroporin, AQP10 (AQP10+ enterocyte), that is enriched in children from the US. We show that emergence of this enterocyte state depends on lipid exposure to intestinal stem cells and correlates with dietary fat intake. We also identify a previously-undescribed thyrotropin-releasing hormone (TRH+) enteroendocrine cell and provide evidence for a local endocrine-epithelial-lymphocyte circuit. Our work establishes a detailed framework for pediatric duodenal mucosal development and illuminates how intestinal cellular dynamics are shaped by age and environment.

developmental biology↗

bioRxiv2025

Synthetic Control of Implanted Engineered Liver Tissue Growth

Despite the promise of engineered tissue implants for the treatment of organ failure, scaling of these constructs to sizes of therapeutic relevance remains a barrier to clinical translation. Here, we propose a strategy to circumvent this limitation: to instead implant a small-scale construct and then induce it to grow in situ after its engraftment into a host. Using engineered liver tissue as a proof-of-concept application, we integrated synthetic biology and tissue engineering tools to build liver tissues that can be expanded on-demand after implantation in vivo. To achieve this goal, we first identified the combination of YAP and growth factor signaling as sufficient to drive human hepatocyte proliferation in dense, 3D engineered tissues. We then engineered control of these signaling axes using synthetic biology tools to drive human liver tissue expansion both in vitro and in vivo. As such, this work establishes a genetic strategy for generating large organ implants through bioengineered, on-demand outgrowth using synthetic triggers (BOOST). TeaserPresenting bioengineered on-demand outgrowth via synthetic biology triggering (BOOST) for in situ solid cell therapy scale up.

bioengineering↗

bioRxiv2025

Diffusion-based Representation Integration for Foundation Models Improves Spatial Transcriptomics Analysis

MotivationWe propose DRIFT, a framework that integrates spatial context into the input representations for foundation models by leveraging diffusion on spatial graphs derived from spatial transcriptomics (ST) data. ST captures gene expression profiles while preserving spatial context, enabling downstream analysis tasks such as cell-type annotation, clustering, and cross-sample alignment. However, due to its emerging nature, there are very few foundation models that can utilize ST data to generate embeddings generalizable across multiple tasks. Meanwhile, well-documented foundational models trained on large-scale single-cell gene expression (scRNA-seq) data have demonstrated generalizable performance across scRNA-seq assays, tissues, and tasks; however, they do not leverage the spatial information in ST data. We use heat kernel diffusion to propagate embeddings across spatial neighborhoods, incorporating the local neighborhood context of the ST data while preserving the transcriptomic representations learned by state-of-the-art single-cell foundation models. ResultsWe systematically benchmark five foundational models (both scRNA-seq and ST-based) across key ST tasks such as annotation, alignment, and clustering, ensuring a comprehensive evaluation of our proposed framework. Our results show that DRIFT significantly improves the performance of existing foundational models on ST data over specialized state-of-the-art methods. Overall, DRIFT is an effective, accessible, and generalizable framework that bridges the gap toward universal models for modeling spatial transcriptomics. Availability and ImplementationCode and data available at https://github.com/rsinghlab/DRIFT. Contactritambhara@brown.edu Supplementary informationSupplementary notes are provided with the manuscript.

bioinformatics↗

bioRxiv2025

A Reference Atlas of the Human Dorsal Root Ganglion

Somatosensory perception largely emerges from diverse peripheral sensory neurons whose cell bodies reside in dorsal root ganglia (DRG). Damage or dysfunction of DRG neurons is a major cause of chronic pain and sensory loss. In mice, deep single-cell transcriptomic profiling and genetically defined models have offered important clues into DRG function, but in humans, the cellular and molecular landscape of DRG neurons remains less understood. Here, we constructed a reference cell atlas of the human DRG by profiling transcriptomes of cells and nuclei from 126 donors sampled across cervical, thoracic, and lumbar DRGs. This atlas resolves 22 neuronal subtypes, including known and previously unrecognized subtypes linked to nociception, mechanosensation, thermosensation, and proprioception, as well as 10 types of non-neuronal cells. Cross-species integration, spatial transcriptomics, and microneurography enabled cell-type-specific comparisons of soma size and conduction velocity between species. Human DRG somata are larger across all cell types than their mouse counterparts, and the conduction velocities of human hair follicle innervating A-fibers are faster than in mice, suggesting a functional shift in rapid mechanical detection in humans. This integrated human DRG reference cell atlas provides a resource for exploring new molecular and physiological features of human DRG, which could help identify new strategies for treating chronic pain and other diseases of the peripheral nervous system.

neuroscience↗

bioRxiv2025

Blind Prediction of Complex Water and Ion Ensembles Around RNA in CASP16

Biomolecules rely on water and ions for stable folding, but these interactions are often transient, dynamic, or disordered and thus hidden from experiments and evaluation challenges that represent biomolecules as single, ordered structures. Here, we compare blindly predicted ensembles of water and ion structure to the cryo-EM densities observed around the Tetrahymena ribozyme at 2.2-2.3 [A] resolution, collected through target R1260 in the CASP16 competition. 26 groups participated in this solvation cryo-ensemble prediction challenge, submitting over 350 million atoms in total, offering the first opportunity to compare blind predictions of dynamic solvent shell ensembles to cryo-EM density. Predicted atomic ensembles were converted to density through local alignment and these densities were compared to the cryo-EM densities using Pearson correlation, Spearman correlation, mutual information, and precision-recall curves. These predictions show that an ensemble representation is able to capture information of transient or dynamic water and ions better than traditional atomic models, but there remains a large accuracy gap to the performance ceiling set by experimental uncertainty. Overall, molecular dynamics approaches best matched the cryo-EM density, with blind predictions from bussilab_plain_md, SoutheRNA, bussilab_replex, coogs2, and coogs3 outperforming the baseline molecular dynamics prediction. This study indicates that simulations of water and ions can be quantitatively evaluated with cryo-EM maps. We propose that further community-wide blind challenges can drive and evaluate progress in modeling water, ions and other previously hidden components of biomolecular systems.

biophysics↗

bioRxiv2025

Regulation of cell proliferation by a novel feedback system on Cdk function

The proliferation of eukaryotic cells is regulated by a complex network of regulatory systems that promotes efficient cell cycle progression and ensures proper responses to the environment. Despite this complexity, the core inputs that are necessary and sufficient for robust alternation of DNA replication and mitosis are surprisingly simpler than anticipated. Indeed, fission yeast cells operating with an engineered minimal cell cycle network that lacks the highly conserved Wee1+Cdc25 feedback loops on Cdk1 function are viable, although slow growing. This provides a unique entry for evaluating how such simplified cells can evolve and improve their proliferation potential while exploring unknown mechanisms modulating cell cycle progression. Taking advantage of this model, we applied laboratory evolution assays to minimal fission yeast backgrounds and selected for the emergence of faster growing populations. We found that loss of the small disordered protein Spo12 brings about enhanced population growth in cells lacking the Wee1+Cdc25 mitotic switch. Importantly, we demonstrate that Spo12 defines a new and conserved family of inhibitors of the Cdk-counteracting phosphatase PP2A that are directly regulated by Cdk-dependent phosphorylation. Our results also reveal a trade-off associated with Spo12-dependent regulation, which may have implications for our understanding of the principles underlying the evolution of cell cycle control. Finally, our study highlights how combining simplified circuits with experimental evolution allows for uncovering regulatory elements that may be obscured by network complexity.

cell biology↗

bioRxiv2025

Alternative splicing of synaptotagmin 7 regulates oligomerization and short-term synaptic plasticity

Synaptic plasticity is crucial for learning and memory. The presynaptic calcium sensor synaptotagmin 7 (syt7) regulates aspects of short-term plasticity (STP), but the underlying mechanisms remain unclear. Here, we show that alternative splicing of the syt7 juxtamembrane linker acts as a molecular switch at both biochemical and functional levels. The and {beta} variants undergo liquid-liquid phase separation to form condensates, while the {gamma} variant forms aggregates. Using iGluSnFR imaging, we found that when expressed at equal levels, these three isoforms also diverge regarding their abilities to regulate two key aspects of STP: paired-pulse facilitation and synaptic depression. STED microscopy showed that all three isoforms form active zone-associated clusters that colocalize with syt1, while MINFLUX super-resolution microscopy resolved syt7 clusters within the active zone, well-positioned to directly control synaptic vesicle dynamics. Thus, alternative splicing might fine-tune STP by differentially impacting syt7 oligomerization.

neuroscience↗

bioRxiv2025

Sudden Death-Associated KCNH2 Variants Have Opposing Effects on hERG1NP Function

hERG1NP is a non-conducting subdomain of the full-length hERG1 channel that is expressed in the nuclei of developing cardiomyocytes. From the nucleus, hERG1NP modulates gating and expression of the full-length hERG1 channel. hERG1NP variants are linked with sudden death in the young, but the impact of these variants on hERG1NP activity has not been studied. To determine the effect of hERG1NP variants on hERG1NP activity, we measured hERG1NP intracellular localization and modulation of membrane current from the full-length hERG1a channel in HEK293 cells. The wildtype hERG1NP suppressed both hERG1a current (IhERG) and protein. We then screened six hERG1NP variants for changes in either intracellular targeting or modulation of hERG1a current. Two variants, R885C and R1047L, disrupted hERG1NP activity by altering nuclear transport or abolishing both IhERG current suppression and nuclear targeting, respectively. Two additional variants, G1036D and Q1068R, enhanced hERG1NP activity by depolarizing hERG1as voltage dependence of activation via accelerated channel deactivation and recovery from inactivation. Lastly, two variants had no effect: R1035W and R1069S. This work demonstrates that hERG1NP variants associated with sudden death in the young can trigger both loss-of-function and gain-of-function effects on hERG1NP. Additional work is needed to identify specific pathogenic mechanisms of hERG1NP variants.

cell biology↗

bioRxiv2025

Structural proteomics of the human ubiquitinome

The proteasome maintains the integrity of eukaryotic proteomes by selectively degrading ubiquitinated protein substrates. Ubiquitination targets a wide range of substrates for degradation, including translationally stalled nascent chains, misfolded proteins, and properly folded but short-lived proteins destined for regulatory degradation. Distinct structural features and ubiquitination patterns across these classes of substrates remain largely undefined. In this study, we combine structural proteomics and time-resolved isotopic labeling to profile the modification sites, dynamics, and conformational properties of the human ubiquitinome. We show that proteins undergoing rapid proteasomal degradation are ubiquitinated at lysine residues that are normally buried within structured regions of their native conformations. We provide proteome-wide evidence that this high-flux subset of the ubiquitinome is enriched in newly synthesized proteins that have non-native conformations. Together, our findings demonstrate how the lack of structural integrity of misfolded nascent proteins influences their ubiquitination patterns and ensures proper proteasomal degradation. Significance StatementProtein degradation by the ubiquitin-proteasome system (UPS) is central to maintaining cellular protein quality control, yet the structural and kinetic determinants that govern which proteins are targeted for degradation remain poorly defined. Using deep-coverage structural proteomics combined with metabolic labeling, we show that ubiquitination events can be categorized into two broad classes with distinct properties: those at buried lysines within nascent misfolded proteins that lead to rapid proteasomal degradation, and those at exposed lysines in mature proteins that are associated with slower turnover or regulatory functions. This proteome-wide partitioning provides structural insights into how the UPS targets defective nascent and mature proteins for proteasomal clearance.

molecular biology↗

bioRxiv2025

A distal promoter and aberrant splicing enable canonical translation of out-of-frame proteins in Huntington's disease

Expanded CAG trinucleotide repeats cause more than a dozen neurodegenerative diseases, including Huntingtons disease (HD). In several disorders, these repeats are translated in multiple reading frames without identifiable AUG start codons. This process, called repeat-associated non-AUG (RAN) translation, generates aggregation-prone proteins, but its molecular basis remains unclear. Here, using affinity capture of CAG-repeat-containing RNAs, we identify a previously unannotated promoter ~33 kb upstream of the HTT gene. Transcripts initiating from this promoter undergo repeat-length-dependent aberrant splicing into exon 1 of the canonical HTT, embedding the CAG repeat in AUG-initiated frames encoding polyalanine and polyserine proteins. Comparative genomics indicates that this upstream promoter is primate-specific, helping explain inconsistencies across rodent models. Our findings establish a direct, AUG-dependent, splicing-mediated mechanism for out-of-frame repeat proteins in HD, expose critical gaps in current animal models, and identify novel splice junctions as potential therapeutic targets.

molecular biology↗

bioRxiv2025

Minimal polymerase-containing precursor required for Chikungunya virus RNA synthesis

Alphaviruses pose a growing global health threat, with Chikungunya virus (CHIKV) epidemics ongoing and no safe or effective vaccines or antivirals currently available. The CHIKV nonstructural proteins nsP2 and nsP4 encode essential enzymatic activities that represent key targets for antiviral development, yet the biochemical basis of nsP4 RNA-dependent RNA polymerase (RdRp) activity remains poorly understood. Here, we identify a minimal, functional precursor form of nsP4 derived from the nsP3-nsP4 polyprotein (P34) that is active in a cell-based RNA replicon system. Using synthetic, capped mRNAs, we show that cleavage of P34 by the nsP2 protease is required for robust reporter expression, and that a truncated form retaining only the C-terminal 50 residues of nsP3 (CT50-P34) supports near-wild-type replication. Unexpectedly, ubiquitin-nsP4 fusions failed to substitute for P34, likely reflecting the transient expression supported by our RNA-based system. We propose that precursor forms of nsP4 interact with the nsP1 dodecamer at the site of genome replication, where cleavage activates the RdRp and localization within the nsP1 dodecamer maintains nsP4 in its active conformation. Dissociation from the nsP1 dodecamer triggers a conformational switch to an inactive state. Together, these findings establish a tractable framework for interrogation of the assembly, activation, and regulation of the alphavirus polymerase.

microbiology↗

bioRxiv2025

Polyamine homeostasis in vivo relies primarily on transport

Polyamines are essential metabolites present in all cells, but their regulation in vivo remains poorly understood. Little is known about whether tissues maintain distinct polyamine setpoints, how these setpoints are established, or whether such differences underlie selective vulnerability in disease. Here, we applied single-cell polyamine measurements in living Caenorhabditis elegans to map tissue polyamine levels and their regulatory dependencies. Three principles emerge: (i) Across differentiated tissues, steady-state polyamine pools are maintained primarily by transporter-mediated import rather than de novo synthesis. (ii) The intestine functions as a systemic regulator: perturbing intestinal polyamines affects organism-wide levels, and intestine-specific rescue restores systemic balance. (iii) Neurons maintain markedly low polyamine pools and undergo subtype-specific developmental reprogramming, switching polyamine acquisition strategies as they mature. These findings define core principles of tissue-specific polyamine regulation in vivo and provide a framework for developing therapeutic strategies to restore polyamine balance.

cell biology↗

bioRxiv2025

Sequence-encoded interactions program internal condensate architecture

Many cellular condensates, such as the nucleolus and stress granules, contain multiple coexisting phases with distinct compositions and material properties. This internal organization is crucial for function, yet how it is established remains unclear. Here, using a programmable DNA system, we reveal how molecular interactions can precisely encode multiphase architecture. We find that phase separation drives macromolecules into a semi-dilute regime where subtle differences in homotypic interaction energies are amplified into dominant organizational forces. A critical interaction energy threshold must be overcome to trigger internal demixing, after which molecular partitioning scales near-linearly with interaction strength. This universal relationship is captured by an associative polymer model, and enables engineering of condensates with up to four coexisting phases exhibiting 100-fold differences in viscosity within the same droplet. These design principles extend to RNA-peptide systems, establishing a general framework for how sequence can program hierarchical self-assembly and organize biological matter.

biophysics↗

bioRxiv2025

Compensatory responses to glaucoma pathology in the dorsolateral geniculate nucleus

Glaucoma disrupts the conveyance of retinal signals to visual regions of the brain such as the dorsolateral geniculate nucleus (dLGN) due to degeneration of retinal ganglion cells (RGCs) and their axons. Although plasticity during development allows altered visual experience to modulate dLGN synapses and excitability, evidence for experience-dependent dLGN plasticity in adults is limited. However, glaucoma might trigger compensatory plasticity in adult dLGN, thereby compensating for diminished RGC synaptic drive. Here, we tested this using aged (11-15 month-old) DBA/2J mice, which develop high intraocular pressure and glaucoma. In brain slice recordings, we found that diminished RGC inputs could drive robust action potential firing in dLGN relay neurons that was comparable to controls. This was accompanied by increased intrinsic excitability and decreased magnitude of sustained inhibitory currents from GABA spillover to extrasynaptic receptors. These results implicate multiple cellular and synaptic mechanisms that support signaling despite the diminished RGC inputs in glaucoma. HIGHLIGHTSO_LIRetinogeniculate synapse strength in the dLGN is diminished in the DBA/2J mouse model of glaucoma C_LIO_LIDespite a loss of synaptic strength, retinogeniculate synapses drive robust action potential firing in dLGN relay neurons, suggestive of homeostatic compensation C_LIO_LIdLGN relay neurons from DBA/2J mice have an increase in intrinsic excitability, supporting action potential generation C_LIO_LIReduced extrasynaptic sustained inhibition in DBA/2J dLGN relay neurons can also support synaptically driven action potential firing C_LI

neuroscience↗

bioRxiv2025

Transcriptome-wide analysis reveals sequence selection to avoid mRNA aggregation in E. coli

RNA is built from a four-nucleotide alphabet. Complementary sequences inevitably arise, creating pervasive opportunities for promiscuous RNA-RNA interactions. Here, we show that this chemistry makes the transcriptome intrinsically prone to self-association. We simulated the simultaneous interactions of ~7,500 mRNAs representing the E. coli transcriptome at physiological concentrations. These large-scale simulations predict widespread, dynamic clustering driven by RNA alone and organized by long, multivalent transcripts. Purified mRNA recapitulates this behavior in vitro, with aggregate composition mirroring model predictions. Strikingly, native mRNA sequences are markedly less prone to self-association than matched randomized controls: they fold more stably, expose shorter single-stranded regions, and form weaker intermolecular contacts. Similar signatures are observed in abundant human mRNAs, suggesting that evolution has shaped coding sequences to minimize self-association. These findings identify transcriptome solubility as an unrecognized constraint on mRNA sequence evolution and provide a framework for understanding how cells keep their transcriptomes dispersed and functional.

biophysics↗

bioRxiv2025

A fold switch regulates conformation of an alphavirus virus RNA-dependent RNA polymerase

Alphaviruses are mosquito-vectored, positive-strand RNA viruses causing rheumatic and neurological diseases. Like all RNA viruses, they encode an RNA-dependent RNA polymerase (RdRp, nsP4). Purification of an nsP4 derivative capable of processive RNA synthesis from a heteropolymeric template has been unsuccessful. Prior studies indicated Onyong-nyong virus (ONNV) nsP4 is soluble and requires additional non-structural proteins for activity. We performed biochemical and biophysical characterization of ONNV nsP4, including analytical ultracentrifugation and small-angle X-ray scattering (SAXS), revealing an extended conformation inconsistent with AlphaFold predictions of a compact structure. Fold switching was required for the extended conformation. Hydrogen-deuterium exchange mass spectrometry confirmed the fold-switched, extended state. Phylogenetic analysis showed conservation of residues contributing to both extended and compact states, implying functional roles for each. The extended form exhibited weak RNA binding and no polymerase activity on primed templates. The SAXS envelope of a precursor containing 50 amino acids from the nsP3 C-terminus (CT50-P34) matched the compact state. We propose precursor forms adopt the compact conformation. At the replication site, proteolytic cleavage would convert the precursor to an active polymerase. Polymerase dissociation upon completion of synthesis would induce fold switching to the inactive, extended state, precluding cytoplasmic activity that would activate intracellular immune responses.

biophysics↗

bioRxiv2025

Evaluating Language Models for Biomedical Fact-Checking: A Benchmark Dataset for Cancer Variant Interpretation Verification

Accurate interpretation of genomic variants is critical for precision oncology but remains slow and dependent on specialized expertise. Public knowledgebases such as the Clinical Interpretation of Variants in Cancer (CIViC) help by curating literature-backed variant interpretations in a structured form, yet verification and review have become major bottlenecks. Large language models (LLMs) offer a potential mechanism for accelerating biomedical claim verification, but their rapid turnover, variable availability, and known risks of unsupported reasoning require standardized and reproducible evaluation before integration into curation workflows. To address this, we developed CIViC-Fact, an expert-curated, full-text benchmark and evaluation framework. Domain experts linked structured cancer-variant claims to sentence-level evidence from source publications, including evidence from full-text articles, tables, and non-abstract sections that are commonly omitted from existing biomedical question-answering and scientific fact-checking datasets. Claim-verification reference labels were derived from CIViC records, revision histories and controlled data augmentation. A major finding of CIViC-Fact is that abstracts are insufficient for realistic biomedical claim verification. In the evaluated development subset of text-verifiable entries with full-text access, fewer than 30% could be fully validated from the abstract alone, highlighting the importance of full-text evaluation for biomedical curation. Upon the application of our fact-checking pipeline to newly submitted CIViC entries, after excluding entries requiring supplementary material or images for validation, automated retrieval successfully identified appropriate evidence for most cases (93%), supporting low-incremental-effort evaluation of future systems. Fine-tuning improved agreement with CIViC-Fact reference labels on the static benchmark, but larger general-purpose models performed better on a heterogeneous post-cutoff cohort. These findings support CIViC-Fact primarily as a reproducible framework for comparing evolving retrieval and verification systems rather than as validation of a single deployment-ready model. These findings suggest that, in a rapidly changing model landscape, the durable contribution is not a single optimized model but a reproducible benchmark framework that enables continual testing, model substitution, and lightweight updating through small high-quality few-shot exemplar sets.

bioinformatics↗

bioRxiv2025

The 2'-endo conformation of arabinose-CTP and arabinose-UTP inhibit viral polymerases by inducing long pauses.

Key to supporting human health in the face of evolving viruses is the development of novel antiviral drug scaffolds with the potential for broad inhibition of viral families. Nucleoside analogs are a key class of drugs that have demonstrated potential for the inhibition of several viral species. Here, we evaluate arabinose nucleotides (ara-NTP) as inhibitors of the SARS-CoV-2 and poliovirus polymerases using biochemistry, biophysics and structural biology. Ara-NTPs compete poorly with their natural counterparts for incorporation into RNA by viral polymerases. However, upon incorporation, ara-NMPs induce long polymerase pausing in both SARS-CoV-2 and poliovirus polymerase RNA elongation. Our studies suggest that subsequent nucleotide incorporation is inhibited at the catalytic step due to the 2-endo sugar pucker of the incorporated ara-NMP.

biochemistry↗