Biology subjects

Gartner, Z. J.

Publications and source records attributed to Gartner, Z. J..

34 records · Page 2Linked to original sources

bioRxiv2021

Lineage Recording Reveals the Phylodynamics, Plasticity and Paths of Tumor Evolution

Tumor evolution is driven by the progressive acquisition of genetic and epigenetic alterations that enable uncontrolled growth, expansion to neighboring and distal tissues, and therapeutic resistance. The study of phylogenetic relationships between cancer cells provides key insights into these processes. Here, we introduced an evolving lineage-tracing system with a single-cell RNA-seq readout into a mouse model of Kras;Trp53(KP)-driven lung adenocarcinoma which enabled us to track tumor evolution from single transformed cells to metastatic tumors at unprecedented resolution. We found that loss of the initial, stable alveolar-type2-like state was accompanied by transient increase in plasticity. This was followed by adoption of distinct fitness-associated transcriptional programs which enable rapid expansion and ultimately clonal sweep of rare, stable subclones capable of metastasizing to distant sites. Finally, we showed that tumors develop through stereotypical evolutionary trajectories, and perturbing additional tumor suppressors accelerates tumor progression by creating novel evolutionary paths. Overall, our study elucidates the hierarchical nature of tumor evolution, and more broadly enables the in-depth study of tumor progression.

cancer biology↗

bioRxiv2021

T cell circuits that sense antigen density with an ultrasensitive threshold

Overexpressed tumor associated antigens (e.g. HER2 and EGFR) are attractive targets for therapeutic T cells, but toxic cross-reaction with normal tissues expressing low antigen levels has been observed with Chimeric Antigen Receptor (CAR) T cells targeting such antigens. Inspired by natural ultrasensitive response circuits, we engineer a two-step positive feedback circuit that allows T cells to discriminate targets based on a sigmoidal antigen density threshold. In this circuit, a low affinity SynNotch receptor for HER2 controls the expression of a high affinity CAR for HER2. Increasing HER2 density thus has cooperative effects on T cells it both increases CAR expression and activation leading to a sigmoidal response. T Cells with this circuit show sharp discrimination between target cells expressing normal and disease levels of HER2, both in vitro and in vivo. One Sentence SummaryA two-step positive feedback circuit generates engineered T cells capable of killing target cells with an ultrasensitive antigen density threshold.

synthetic biology↗

bioRxiv2021

Single Cell Enhancer Activity Maps Neuronal Lineages in Embryonic Mouse Basal Ganglia

Enhancers integrate transcription factor signaling pathways that drive cell fate specification in the developing brain. We used single cell RNA-sequencing (scRNA-seq) to capture enhancer activity at single cell resolution and delineate specification of cells labeled by enhancers in mouse medial, lateral, and caudal ganglionic eminences (MGE, LGE, and CGE) at embryonic day (E)11.5. We combine enhancer-based reporter labeling with single-cell transcriptional readout to characterize enhancer activity and define cell populations in vivo. Seven enhancers had diverse activities in specific progenitor and neuronal populations within the GEs. We then applied enhancer-based labeling, scRNA-seq, and analysis of in situ hybridization (ISH) data to distinguish subtypes of MGE-derived GABAergic and cholinergic projection neurons and interneurons. This work demonstrates how the power of scRNA-seq can be extended by enhancer-based labelling and leveraging ISH data and reveals novel lineage specification paths underlying patterning of developing mouse brain.

neuroscience↗

bioRxiv2021

Systematically quantifying morphological features reveals constraints on organoid phenotypes

Organoids recapitulate complex 3D organ structures and represent a unique opportunity to probe the principles of self-organization. While we can alter an organoids morphology by manipulating the culture conditions, the morphology of an organoid often resembles that of its original organ, suggesting that organoid morphologies are governed by a set of tissue-specific constraints. Here, we establish a framework to identify constraints on an organoids morphological features by quantifying them from microscopy images of organoids exposed to a range of perturbations. We apply this framework to Madin-Darby Canine Kidney cysts and show that they obey a number of constraints taking the form of scaling relationships or caps on certain parameters. For example, we found that the number, but not size, of cells increases with increasing cyst size. We also find that these constraints vary with cyst age and can be altered by varying the culture conditions. We observed similar sets of constraints in intestinal organoids. This quantitative framework for identifying constraints on organoid morphologies may inform future efforts to engineer organoids.

systems biology↗

bioRxiv2020

Size-dependent protein segregation creates a spatial switch for Notch and APP signaling

Aberrant cleavage of Notch by {gamma}-secretase is implicated in numerous diseases, but how cleavage is regulated in space and time is unclear. Here, we report that cadherin-based adherens junctions (cadAJs) are sites of high cell-surface {gamma}-secretase activity, as well as sites of constrained physical space that excludes {gamma}-secretase substrates having large extracellular domains (ECDs) like Notch. ECD shedding initiates drastic spatial relocalization of Notch to cadAJs, allowing enzyme-substrate interactions and downstream signaling. Spatial mutations by adjusting the ECD size or the physical constraint alter signaling. Dysregulation of this spatial switch promotes precocious differentiation of ventricular zone neural progenitor cells in vivo. We show the generality of this spatial switch for amyloid precursor protein proteolysis. Thus, cadAJs create spatially distinct biochemical compartments regulating cleavage events involving {gamma}-secretase and preventing aberrant activation of receptors. One Sentence SummaryNotch cleavage by {gamma}-secretase is regulated through dynamic spatial control of receptors, adhesion molecules, and activating proteases

cell biology↗

bioRxiv2020

Human microglia upregulate cytokine signatures and accelerate maturation of neural networks

Microglia are the resident macrophages of the brain that emerge in early development and play vital role disease states, as well as in normal development. Many fundamental questions about microglia diversity and function during human brain development remain unanswered, as we currently lack cellular-resolution datasets focusing on microglia in developing primary tissue, or experimental strategies for interrogating their function. Here, we report an integrative analysis of microglia throughout human brain development, which reveals molecular signatures of stepwise maturation, as well as human-specific cytokine-associated subtype that emerges around the onset of neurogenesis. To demonstrate the utility of this atlas, we have compared microglia across several culture models, including cultured primary microglia, pluripotent stem cell-derived microglia. We identify gene expression signatures differentially recruited and attenuated across experimental models, which will accelerate functional characterization of microglia across perturbations, species, and disease conditions. Finally, we identify a role for human microglia in development of synchronized network activity using a xenotransplantation model of human microglia into cerebral organoids.

developmental biology↗

bioRxiv2020

No detectable alloreactive transcriptional responses during donor-multiplexed single-cell RNA sequencing of peripheral blood mononuclear cells

Single-cell RNA sequencing (scRNA-seq) provides high-dimensional measurement of transcript counts in individual cells. However, high assay costs limit the study of large numbers of samples. Sample multiplexing technologies such as antibody hashing and MULTI-seq use sample-specific sequence tags to enable individual samples (e.g., different patients) to be sequenced in a pooled format before downstream computational demultiplexing. Critically, no study to date has evaluated whether the mixing of samples from different donors in this manner results in significant changes in gene expression resulting from alloreactivity (i.e., response to non-self immune antigens). The ability to demonstrate minimal to no alloreactivity is crucial to avoid confounded data analyses, particularly for cross-sectional studies evaluating changes in immunologic gene signatures. Here, we compared the expression profiles of peripheral blood mononuclear cells (PBMCs) from a single donor with and without pooling with PBMCs isolated from other donors with different blood types. We find that there was no evidence of alloreactivity in the multiplexed samples following three distinct multiplexing workflows (antibody hashing, MULTI-seq, and in silico genotyping using souporcell). Moreover, we identified biases amongst antibody hashing sample classification results in this particular experimental system, as well as gene expression signatures linked to PBMC preparation method (e.g., Ficoll-Paque density gradient centrifugation with or without apheresis using Trima filtration).

genomics↗

bioRxiv2020

ZipSeq : Barcoding for Real-time Mapping of Single Cell Transcriptomes

Spatial transcriptomics seeks to integrate single-cell transcriptomic data within the 3-dimensional space of multicellular biology. Current methods use glass substrates pre-seeded with matrices of barcodes or fluorescence hybridization of a limited number of probes. We developed an alternative approach, called ZipSeq, that uses patterned illumination and photocaged oligonucleotides to serially print barcodes (Zipcodes) onto live cells within intact tissues, in real-time and with on-the-fly selection of patterns. Using ZipSeq, we mapped gene expression in three settings: in-vitro wound healing, live lymph node sections and in a live tumor microenvironment (TME). In all cases, we discovered new gene expression patterns associated with histological structures. In the TME, this demonstrated a trajectory of myeloid and T cell differentiation, from periphery inward. A variation of ZipSeq efficiently scales to the level of single cells, providing a pathway for complete mapping of live tissues, subsequent to real-time imaging or perturbation.

genomics↗

bioRxiv2019

Lactoferrin Reverses Methotrexate Driven Epithelial Barrier Defect by Inhibiting TGF-β Mediated Epithelial to Mesenchymal Transition

BACKGROUND AND AIMSMethotrexate is an important tool in the arsenal of oncologists, gastroenterologists, and rheumatologists. At low doses it induces intestinal barrier dysfunction that may induce side effects such as gastrointestinal discomfort and liver injury. Previous studies suggest that lactoferrin can improve barrier function in a variety of contexts. This study set out to determine the mechanism of methotrexate induced barrier dysfunction and assess the effect of lactoferrin and other components of human breast milk on this dysfunction. METHODSUsing a murine enteroid model and Caco2 spheroids, we measured flux of basolateral-administered fluorescent dextran into the lumen. Barrier dysfunction was induced using methotrexate (220 nM) or lipopolysaccharide (20 nM). Human lactoferrin was added at 0.8 mg/ml (10 {micro}M). RNAseq was performed on exposed samples. RESULTSLactoferrin blocks methotrexate-induced barrier dysfunction in murine enteroids. Similar results were observed when barrier dysfunction was induced in Caco2 spheroids with methotrexate and LPS, but not ML7. RNAseq revealed activation of TGF-{beta} response genes and epithelial-mesenchymal transition (EMT) by methotrexate, which normalized in the presence of lactoferrin. TGF-{beta} receptor inhibition (RepSox) blocked methotrexate induced barrier dysfunction in Caco2 spheroids. 20 nM TGF-{beta} induced barrier dysfunction in Caco2 spheroids which was also inhibited by lactoferrin. CONCLUSIONSMethotrexate induces barrier dysfunction by activation of an EMT program promoted by TGF-{beta} signaling and inhibited by lactoferrin. Lactoferrin is also protective of barrier function in an LPS-induced model. The likely mechanism of this effect is blockade of EMT programs induced by TGF-{beta}.

cell biology↗

bioRxiv2019

Linked optical and gene expression profiling of single cells at high throughput

Single cell RNA sequencing has emerged as a powerful tool for characterizing cells, but not all phenotypes of interest can be observed through gene expression alone. Linking sequencing with optical analysis has provided insight into the molecular basis behind cellular function, but current approaches have limited throughput. Here, we present a high throughput platform for linked optical and gene expression profiling of single cells. We demonstrate accurate fluorescence and gene expression measurements from thousands of cells in a single experiment and use the platform to characterize DNA and RNA changes in Jurkat cells through the cell cycle. In addition to its scalability, our integration of microfluidics and array-based molecular biology holds promise for comprehensive multi-omics profiling of single cells.

bioengineering↗

bioRxiv2018

Mapping the complex paracrine response to hormones in the human breast at single-cell resolution

The human breast undergoes lifelong remodeling in response to estrogen and progesterone, but hormone exposure also increases breast cancer risk. Here, we use single-cell analysis to identify distinct mechanisms through which breast composition and cell state affect hormone signaling. We show that prior pregnancy reduces the transcriptional response of hormone-responsive (HR+) epithelial cells, whereas high body mass index (BMI) reduces overall HR+ cell proportions. These distinct changes both impact neighboring cells by effectively reducing the magnitude of paracrine signals originating from HR+ cells. Because pregnancy and high BMI are known to protect against hormone-dependent breast cancer in premenopausal women, our findings directly link breast cancer risk with person-to-person heterogeneity in hormone responsiveness. More broadly, our findings illustrate how cell proportions and cell state can collectively impact cell communities through the action of cell-to-cell signaling networks.

systems biology↗

bioRxiv2018

MULTI-seq: Scalable sample multiplexing for single-cell RNA sequencing using lipid-tagged indices

We describe MULTI-seq: A rapid, modular, and universal scRNA-seq sample multiplexing strategy using lipid-tagged indices. MULTI-seq reagents can barcode any cell type from any species with an accessible plasma membrane. The method is compatible with enzymatic tissue dissociation, and also preserves viability and endogenous gene expression patterns. We leverage these features to multiplex the analysis of multiple solid tissues comprising human and mouse cells isolated from patient-derived xenograft mouse models. We also utilize MULTI-seqs modular design to perform a 96-plex perturbation experiment with human mammary epithelial cells. MULTI-seq also enables robust doublet identification, which improves data quality and increases scRNA-seq cell throughput by minimizing the negative effects of Poisson loading. We anticipate that the sample throughput and reagent savings enabled by MULTI-seq will expand the purview of scRNA-seq and democratize the application of these technologies within the scientific community.

genomics↗

bioRxiv2018

DoubletFinder: Doublet detection in single-cell RNA sequencing data using artificial nearest neighbors

Single-cell RNA sequencing (scRNA-seq) using droplet microfluidics occasionally produces transcriptome data representing more than one cell. These technical artifacts are caused by cell doublets formed during cell capture and occur at a frequency proportional to the total number of sequenced cells. The presence of doublets can lead to spurious biological conclusions, which justifies the practice of sequencing fewer cells to limit doublet formation rates. Here, we present a computational doublet detection tool - DoubletFinder - that identifies doublets based solely on gene expression features. DoubletFinder infers the putative gene expression profile of real doublets by generating artificial doublets from existing scRNA-seq data. Neighborhood detection in gene expression space then identifies sequenced cells with increased probability of being doublets based on their proximity to artificial doublets. DoubletFinder robustly identifies doublets across scRNA-seq datasets with variable numbers of cells and sequencing depth, and predicts false-negative and false-positive doublets defined using conventional barcoding approaches. We anticipate that DoubletFinder will aid in scRNA-seq data analysis and will increase the throughput and accuracy of scRNA-seq experiments.

bioinformatics↗

bioRxiv2017

Printed Droplet Microfluidics for on demand dispensing of picoliter droplets and cells

Although the elementary unit of biology is the cell, high throughput methods for the microscale manipulation of cells and reagents are limited. The existing options are either slow, lack single cell specificity, or utilize fluid volumes out of scale with those of cells. Here, we present Printed Droplet Microfluidics, a technology to dispense picoliter droplets and cells with deterministic control. The core technology is a fluorescence-activated droplet sorter coupled to a specialized substrate that together act as a picoliter droplet and single cell printer, enabling high throughput generation of intricate arrays of droplets, cells, and microparticles. Printed Droplet Microfluidics provides a programmable and robust technology to construct arrays of defined cell and reagent combinations and to integrate multiple measurement modalities together in a single assay.

bioengineering↗

bioRxiv2017

Tissue Folding by Mechanical Compaction of the Mesenchyme

Many tissues fold during development into complex shapes. Engineering this process in vitro would represent an important advance for tissue engineering. We use embryonic tissue explants, finite element modeling, and 3D cell patterning techniques to show that a mechanical compaction of the ECM during mesenchymal condensation can drive tissue folding along programmed trajectories. The process requires cell contractility, generates strains at nearby tissue interfaces, and causes specific patterns of collagen alignment around and between condensates. Aligned collagen fibers support elevated tensions that promote the folding of interfaces along paths that can be predicted by finite element modeling. We demonstrate the robustness and versatility of this strategy for sculpting tissue interfaces by directing the morphogenesis of a variety of folded tissue forms from engineered patterns of mesenchymal condensates. These studies provide insight into the active mechanical properties of the embryonic mesenchyme and establish entirely new strategies for more robustly directing tissue morphogenesis ex vivo, without genetic engineering.

bioengineering↗

bioRxiv2017

Quantius: Generic, high-fidelity human annotation of scientific images at 105-clicks-per-hour

We describe Quantius, a crowd-based image annotation platform that provides an accurate alternative to task-specific computational algorithms for difficult image analysis problems. We use Quantius to quantify a variety of computationally challenging medium-throughput tasks with ~50x and 30x savings in analysis time and cost respectively, relative to a single expert annotator. We show equivalent deep learning performance for Quantius- and expert-derived annotations, bridging towards scalable integration with tailored machine-learning algorithms.

bioinformatics↗