Biology subjects

Zhong, A.

Publications and source records attributed to Zhong, A..

12 recordsLinked to original sources

bioRxiv2026

Timed binary WNT activity is sufficient to model the early human neural axis

The vertebrate nervous system develops into functionally distinct domains along the body axis[1]. Developmental studies implicate multiple signaling pathways in coordinating this process, but the order of specification events, sufficiency of individual signals, and molecular basis of competency remain unclear [2,3], leaving the field without a unified model of neuraxis patterning. Enteric nervous system (ENS) and midbrain dopaminergic (mDA) progenitors have reached clinical and preclinical testing [4-11], yet neither is produced at full purity, and yields vary markedly across human pluripotent stem cell (hPSC) lines, reflecting incomplete control of axial identity. Here we use single-cell genetic fate mapping to demonstrate that hPSCs can commit to anterior or posterior cranial fate within the first 24 hours of differentiation, before neural induction. Building on this finding, we show that the duration of a single saturating WNT pulse is sufficient to specify three 'first-order' domains: anterior cranial (0 h), posterior cranial (24 h) and trunk (48 h), each pre-neural and competent for CNS, neural crest and epidermal lineages. Nested 'second-order' domains are specified within first-order domains in response to WNT, FGF, and retinoic acid. Mechanistically, an anterior gene regulatory network repressing WNT targets is irreversibly shut down during the transition to posterior identities. Applying this binary WNT patterning logic, we generate mDA neurons and ENS progenitors robustly across hPSC lines and establish an assembloid model combining first-order progenitors to produce all major regions of the nervous system.

developmental biology↗

bioRxiv2026

A human developmental and adult brain atlas benchmarks dopaminergic stem cell models and cell therapy candidates

Parkinsons disease (PD) is characterized by the progressive loss of midbrain dopaminergic (mDA) neurons1. Stem cell-derived mDA neurons hold promise for disease modelling2,3 and are currently in clinical trials for cell replacement therapy4-6. However, systematic benchmarking has been limited by the lack of a unified high-resolution reference and methods that quantify incomplete or mixed lineage specification in vitro7. We establish a single-cell and spatial atlas of the human developing diencephalon-midbrain-hindbrain axis resolving 93 cell subtypes, including 39 lacking prior single-cell characterization and 4 entirely novel populations. Using this atlas as a reference, we integrate 19 hPSC-derived mDA datasets, both published2,8-25 and unpublished, to build the Human Dopaminergic Neural Atlas (HDNA) spanning 2D, 3D, and graft models, including those used in clinical trials. To classify cells and quantify lineage fidelity, we develop CapybaraBrain, a marker-driven non-negative decomposition framework that assigns each cell continuous identity scores across all 93 developmental programs, enabling systematic discrimination of discrete, transitioning, and cross-lineage hybrid states26. We uncover a pervasive landscape of off-target populations reflecting relaxed transcriptional boundaries in vitro, including a previously unrecognized TH-PITX2 midbrain neuronal population, and we validate atlas-predicted latent lineage plasticity through inducible genetic fate mapping in mouse models. We further define maturation-associated transcriptional programs by harmonizing adult mDA subtype atlases, revealing that dopaminergic identity and maturation are partially decoupled across protocols. Finally, projecting PD patient-derived tri-cultures onto the HDNA uncovers genotype- and cell-type-specific transcriptional dysregulation. Together, these integrated atlases and computational framework establish a unified standard for benchmarking differentiation fidelity, exposing off-target states, and guiding next-generation PD models and cell therapies.

Developmental Biology↗

bioRxiv2025

A stem cell knockout village reveals lineage rewiring and a non-canonical islet cell fate in monogenic diabetes

Genetics studies have identified a core set of regulators essential for pancreatic {beta} cell development, many of which are mutated in monogenic diabetes. However, how these mutations alter developmental trajectories to produce pathological cell states remains elusive. Here we introduce a knockout village framework that enables longitudinal scRNA-seq profiling of 79 human pluripotent stem cell mutant lines targeting 30 developmental regulators, including 15 diabetes genes, across five islet differentiation stages. We show that loss of lineage regulators impairs {beta} cell formation in a stage-specific manner and rewires developmental trajectories towards competing lineages. Notably, several monogenic diabetes gene mutations drive a shift from {beta} cells to enterochromaffin (EC)-like cells, a recently recognized non-canonical islet cell fate. These EC-like cells exhibit incomplete activation of hormone regulation programs, along with elevated neuron signatures. Leveraging the diversity of cell fate outcomes across mutants, we predicted and experimentally validated ISL1 as a key downstream effector of PDX1 and PAX6 that safeguards {beta} cell identity against an EC-like fate. Together, our findings reveal cell fate rewiring as a widespread, previously underappreciated pathological mechanism in monogenic diabetes and establish a scalable platform for uncovering developmental vulnerabilities in human genetic disorders.

developmental biology↗

bioRxiv2025

Interpretable Thermodynamic Score-based Classification of Relaxation Excursions

Classifying cellular states from high-dimensional molecular and genomic measurements requires methods that provide not only accurate predictions but also calibrated uncertainty and interpretability. Current nonlinear classifiers offer accuracy but often lack uncertainty quantification and mechanistic insights into the features that matter most. We introduce Keeping SCORE, a framework that transforms conditional diffusion models into probabilistic engines for classification and regression by computing exact likelihoods along stochastic noising trajectories. We first benchmark Keeping SCORE on image recognition tasks (handwritten digits, natural photos). We then apply Keeping SCORE to single-cell transcriptomics across a 22-million-cell atlas, classifying 164 cell types with accuracy matching or exceeding state-of-the-art methods, while uniquely providing posterior probability estimates and prediction confidence. For genetic perturbation mapping across 100 CRISPRi conditions in a multi-study Perturb-seq dataset, our approach again matches or surpasses discriminative baselines, with feature-level attributions identifying which genomic features drive each decision. Applied to large-scale protein sequence data, our framework accurately regresses mutational stability effects, attributing them quantitatively to positions along the input sequence. Keeping SCORE requires no retraining or architectural changes to existing diffusion models, providing portable, interpretable, and uncertainty-aware predictions for biological discovery.

bioinformatics↗

bioRxiv2025

Human iPSC derived alveolar macrophages reveal macrophage subtype specific functions of itaconate in M. tuberculosis host defense

Mycobacterium tuberculosis (Mtb) must survive within multiple macrophage populations during infection, including alveolar macrophages (AM) and recruited inflammatory macrophages. In mice, itaconate, produced in macrophages by ACOD1 mediated decarboxylation of aconitate, has direct antimicrobial activity, modulates inflammatory cytokines, and is required for resistance to M. tuberculosis (Mtb) infection. The role of itaconate in human macrophages is less clear and whether itaconate mediates distinct effects in macrophage subtypes is unknown. Here, we investigated the role of itaconate in human iPSC-derived macrophages, either induced by GM-CSF to resemble alveolar macrophages (AM-Like cells), or treated with M-CSF to generate control macrophages (MCDM cells). Both types of human macrophages produce substantially less itaconate than mouse macrophages and AM-Ls produced 4-fold less itaconate than MCDMs. Surprisingly, ACOD1 deficient AM-L macrophages, but not MCDM macrophages, were permissive for Mtb growth. Moreover, itaconate functioned to dampen the Mtb induced inflammatory response in MCDMs, but not AM-L macrophages, affecting both the Type I IFN and TNF pathways. These results indicate that itaconate is involved in human macrophage responses to TB, with distinct roles in different macrophage subsets. These results also show that genetically tractable hiPSC-derived macrophages are a robust and versatile model to dissect cellular host pathogen interactions.

immunology↗

bioRxiv2024

Gut Bacteria Encode Reductases that Biotransform Steroid Hormones

The metabolism of steroids by the gut microbiome affects hormone homeostasis, impacting host development, mental health, and reproductive functions. In this study, we identify the {Delta}4-3-ketosteroid 5{beta}-reductase, 3{beta}-hydroxysteroid dehydrogenase/{Delta}5-4 isomerase, and {Delta}6-3-ketosteroid reductase enzyme families encoded by common human gut bacteria. Through phylogenetic reconstruction and mutagenesis, We show that 5{beta}-reductase and {Delta}6-3-ketosteroid reductase have evolved to specialize in converting diverse 3-keto steroid hormones into their 5{beta}- and {Delta}6-reduced derivatives. We also find that the novel 3{beta}-hydroxysteroid dehydrogenase/{Delta}5-4 isomerase is fused with 5{beta}-reductase in multiple species, streamlining the multi-step conversion of pregnenolone, a steroid hormone precursor, into epipregnanolone. Through metagenomic analysis, we reveal that these enzymes are prevalent in healthy populations, being enriched in females over males. These findings provide the molecular basis for studying microbial steroid metabolism in the gut, offering insights into its potential impact on hormonal health in hosts, especially in the context of womens health.

microbiology↗

bioRxiv2024

Leveraging CRISPR activation for rapid assessment of gene editing products in human pluripotent stem cells

Verification of genome editing in human pluripotent stem cells (hPSCs), particularly in silent locus is desirable but challenging because it often requires complex and time-intensive lineage-specific or tissue-specific differentiation to induce their expression. Here, we establish a rapid and effective workflow for the verification of hPSC lines with genome editing in unexpressed genes using CRISPR-mediated transcriptional activation (CRISPRa). We systematically compared the efficiency of various CRISPRa systems in hPSCs, identifying the SAM system as the most potent for activating silent genes in hPSCs. Furthermore, we demonstrated enhanced gene activation by combining the SAM system with TET1, a demethylation module. By inducing targeted gene activation in undifferentiated hPSCs using CRISPRa, we successfully verified single and dual reporter hPSC lines and conducted functional tests of dTAG knock-ins and silent gene knockouts within 48 hours. This approach eliminates the need for cell differentiation to access genes only expressed by differentiated cells, offering a handy assay for verifying gene editing in hPSCs.

cell biology↗

bioRxiv2024

A robust and inducible precise genome editing via an all-in-one prime editor in human pluripotent stem cells

Prime editing (PE) allows for precise genome editing in human pluripotent stem cells (hPSCs), such as introducing single nucleotide modifications, small deletions, or insertions at a specific genomic locus, a strategy that shows great promise for creating "Disease in a dish" models. To improve the effectiveness of prime editing in hPSCs, we systematically compared and combined the "inhibition of mismatch repair pathway and p53" on top of the "PEmax" to generate an all-in-one "PE-Plus" prime editor. We show that PE-Plus conducts the most efficient editing among the current PE tools in hPSCs. We further established an inducible prime editing platform in hPSCs by incorporating the all-in-one PE vector into a safe-harbor locus and demonstrated temporal control of precise editing in both hPSCs and differentiated cells. By evaluating disease-associated mutations, we show that this platform allows efficient creation of both monoallelic and biallelic disease-relevant mutations in hPSCs. In addition, this platform enables the efficient introduction of single or multiple edits in one step, demonstrating potential for multiplex editing. Therefore, our method presents an efficient and controllable multiplex prime editing tool in hPSCs and their differentiated progeny.

cell biology↗

bioRxiv2023

Discovery of Competent Chromatin Regions in Human Embryonic Stem Cells

The mechanisms underlying the ability of embryonic stem cells (ESCs) to rapidly activate lineage-specific genes during differentiation remain largely unknown. Through multiple CRISPR-activation screens, we discovered human ESCs have pre-established transcriptionally competent chromatin regions (CCRs) that support lineage-specific gene expression at levels comparable to differentiated cells. CCRs reside in the same topological domains as their target genes. They lack typical enhancer-associated histone modifications but show enriched occupancy of pluripotent transcription factors, DNA demethylation factors, and histone deacetylases. TET1 and QSER1 protect CCRs from excessive DNA methylation, while HDAC1 family members prevent premature activation. This "push and pull" feature resembles bivalent domains at developmental gene promoters but involves distinct molecular mechanisms. Our study provides new insights into pluripotency regulation and cellular plasticity in development and disease. One sentence summaryWe report a class of distal regulatory regions distinct from enhancers that confer human embryonic stem cells with the competence to rapidly activate the expression of lineage-specific genes.

developmental biology↗

bioRxiv2023

Functional interrogation of twenty type 2 diabetesassociated genes using isogenic hESC-derived β-like cells

Genetic studies have identified numerous loci associated with type 2 diabetes (T2D), but the functional role of many loci has remained unexplored. In this study, we engineered isogenic knockout human embryonic stem cell (hESC) lines for 20 genes associated with T2D risk. We systematically examined {beta}-cell differentiation, insulin production and secretion, and survival. We performed RNA-seq and ATAC-seq on hESC-{beta} cells from each knockout line. Analyses of T2D GWAS signals overlapping with HNF4A-dependent ATAC peaks identified a specific SNP as a likely causal variant. In addition, we performed integrative association analyses and identified four genes (CP, RNASE1, PCSK1N and GSTA2) associated with insulin production, and two genes (TAGLN3 and DHRS2) associated with sensitivity to lipotoxicity. Finally, we leveraged deep ATAC-seq read coverage to assess allele-specific imbalance at variants heterozygous in the parental hESC line, to identify a single likely functional variant at each of 23 T2D GWAS signals.

genetics↗

bioRxiv2023

Toxic anti-phage defense proteins inhibited by intragenic antitoxin proteins

Recombination-promoting nuclease (Rpn) proteins are broadly distributed across bacterial phyla, yet their functions remain unclear. Here we report these proteins are new toxin-antitoxin systems, comprised of genes-within-genes, that combat phage infection. We show the small, highly variable Rpn C-terminal domains (RpnS), which are translated separately from the full-length proteins (RpnL), directly block the activities of the toxic full-length proteins. The crystal structure of RpnAS revealed a dimerization interface encompassing a helix that can have four amino acid repeats whose number varies widely among strains of the same species. Consistent with strong selection for the variation, we document plasmid-encoded RpnP2L protects Escherichia coli against certain phages. We propose many more intragenic-encoded proteins that serve regulatory roles remain to be discovered in all organisms. SignificanceHere we document the function of small genes-within-genes, showing they encode antitoxin proteins that block the functions of the toxic DNA endonuclease proteins encoded by the longer rpn genes. Intriguingly, a sequence present in both long and short protein shows extensive variation in the number of four amino acid repeats. Consistent with a strong selection for the variation, we provide evidence that the Rpn proteins represent a phage defense system.

microbiology↗

bioRxiv2020

Recurrent evolution of vertebrate transcription factors by transposase capture.

How genes with novel cellular functions evolve is a central biological question. Exon shuffling is one mechanism to assemble new protein architectures. Here we show that DNA transposons, which are mobile and pervasive in genomes, have provided a recurrent supply of exons and splice sites to assemble protein-coding genes in vertebrates via exon-shuffling. We find that transposase domains have been captured, primarily via alternative splicing, to form new fusion proteins at least 94 times independently over [~]350 million years of tetrapod evolution. Evolution favors fusion of transposase DNA-binding domains to host regulatory domains, especially the Kruppel-associated Box (KRAB), suggesting transposase capture frequently yields new transcriptional repressors. We show that four independently evolved KRAB-transposase fusion proteins repress gene expression in a sequence-specific fashion. Genetic knockout and rescue of the bat-specific KRABINER fusion gene in cells demonstrates that it binds its cognate transposons genome-wide and controls a vast network of genes and cis-regulatory elements. These results illustrate a powerful mechanism by which a transcription factor and its dispersed binding sites emerge at once from a transposon family. One Sentence SummaryHost-transposase fusion generates novel cellular genes, including deeply conserved and lineage specific transcription factors.

genomics↗