Biology subjects

Wu, B.

Publications and source records attributed to Wu, B..

190 records · Page 11Linked to original sources

bioRxiv2017

An improved ATAC-seq protocol reduces background and enables interrogation of frozen tissues

We present Omni-ATAC, an improved ATAC-seq protocol for chromatin accessibility profiling that works across multiple applications with substantial improvement of signal-to-background ratio and information content. The Omni-ATAC protocol enables chromatin accessibility profiling from archival frozen tissue samples and 50 m sections, revealing the activities of disease-associated DNA elements in distinct human brain structures. The Omni-ATAC protocol enables the interrogation of personal regulomes in tissue context and translational studies.

genomics↗

bioRxiv2017

Fibroblast Growth Factor Signaling Instructs Ensheathing Glia Wrapping of Drosophila Olfactory Glomeruli

The formation of complex yet highly organized neural circuits requires interactions between neurons and glia. During the assembly of the Drosophila olfactory circuit, 50 olfactory receptor neuron (ORN) classes and 50 projection neuron (PN) classes form synaptic connections in 50 glomerular compartments in the antennal lobe, each of which represents a discrete olfactory information processing channel. Each compartment is separated from the adjacent compartments by membranous processes from ensheathing glia. Here we show that Thisbe, a fibroblast growth factor (FGF) released from olfactory neurons, particularly local interneurons, instructs ensheathing glia to wrap each glomerulus. The Heartless FGF receptor acts cell-autonomously in ensheathing glia to regulate process extension so as to insulate each neuropil compartment. Overexpressing Thisbe in ORNs or PNs causes over-wrapping of glomeruli to which their axons or dendrites target. Failure to establish the FGF-dependent glia structure disrupts precise ORN axon targeting and discrete glomerular formation.\n\nSignificance StatementThis research reports that reciprocal interactions between Drosophila olfactory neurons and ensheathing glia mediate the formation of neuronal compartments--groups of synapses that are packed into discrete structures called glomeruli that carry specific olfactory information. Ensheathing glia respond to a neuronal cue, the fibroblast growth factor (FGF) Thisbe, to pattern the boundaries of the nascent compartments. Neural compartments in turn require such glial barriers to separate themselves from neighboring compartments, so as to ensure the correct organization of the olfactory circuit. These findings highlight the importance of glia in the assembly and maintenance of neural circuits and the functions of FGF signaling in these processes.

neuroscience↗

bioRxiv2017

MEA Viewer: a High-performance Interactive Application for Visualizing Electrophysiological Data

Multi-electrode arrays (MEAs) have been used for many years to measure electrical activity in ensembles of many hundreds of neurons, and are used in research areas as diverse as neuronal connectivity and drug discovery. A high sampling frequency is required to adequately capture action potentials, also known as spikes, the primary electrical event associated with neuronal activity, and the resulting raw data files are large and difficult to visualize with traditional plotting tools. Many common approaches to deal with this issue, such as extracting spikes times and solely performing spike train analysis, significantly reduce data dimensionality. Unbiased data exploration benefits from the use of tools that minimize data transforms and such tools enable the development of heuristic perspective from data prior to any subsequent processing. Here we introduce MEA Viewer, a high-performance interactive application for the direct visualization of multi-channel electrophysiological data. MEA Viewer provides many high-performance visualizations of electrophysiological data, including an easily navigable overview of all recorded extracellular signals overlaid with spike timestamp data and an interactive raster plot. Beyond the fundamental data displays, MEA Viewer can signal average and spatially overlay the extent of action potential propagation within single neurons. This view extracts information below the spike detection threshold to directly visualize the propagation of action potentials across the plane of the MEA. This entirely new method of using MEAs opens up new and novel research applications for medium density arrays. MEA Viewer is licensed under the General Public License version 3, GPLv3, and is available at http://github.com/dbridges/mea-tools.

neuroscience↗

bioRxiv2017

Classifying Drosophila Olfactory Projection Neuron Subtypes by Single-cell RNA Sequencing

How a neuronal cell type is defined and how this relates to its transcriptome are still open questions. The Drosophila olfactory projection neurons (PNs) are among the best-characterized neuronal types: Different PN classes target dendrites to distinct olfactory glomeruli and PNs of the same class exhibit indistinguishable anatomical and physiological properties. Using single-cell RNA-sequencing, we comprehensively characterized the transcriptomes of 40 PN classes and unequivocally identified transcriptomes for 6 classes. We found a new lineage-specific transcription factor that instructs PN dendrite targeting. Transcriptomes of closely-related PN classes exhibit the largest difference during circuit assembly, but become indistinguishable in adults, suggesting that neuronal subtype diversity peaks during development. Genes encoding transcription factors and cell-surface molecules are the most differentially expressed, indicating their central roles in specifying neuronal identity. Finally, we show that PNs use highly redundant combinatorial molecular codes to distinguish subtypes, enabling robust specification of cell identity and circuit assembly.

genomics↗

bioRxiv2017

Structural Basis For The Specific Recognition Of DSR By The YTH Domain Containing Protein Mmi1

Meiosis is one of the most dramatic differentiation programs accompanied by a striking change in gene expression profiles, whereas a number of meiosis-specific transcripts are expressed untimely in mitotic cells. The entry of meiosis will be blocked as the accumulation of meiosis-specific mRNAs during the mitotic cell in fission yeast Schizosaccharomyces pombe. A YTH domain containing protein Mmi1 was identified as a pivotal effector in a post-transcriptional event termed selective elimination of meiosis-specific mRNAs, Mmi1 can recognize and bind a class of meiosis-specific transcripts expressed inappropriately in mitotic cells, which contain a conservative motif called DSR as a mark to remove them in cooperation with nuclear exosomes. Here we report the 1.6 [A] resolution crystal structure of the YTH domain of Mmi1 binds to high-affinity RNA targets r(A1U2U3A4A5A6C7A8) containing DSR core motif. Our structure observations, supported by site-directed mutations of key residues illustrate the mechanism for specific recognition of DSR-RNA by Mmi1. Moreover, different from other YTH domain family proteins, Mmi1 YTH domain has a distinctive function although it has a similar fold as other ones.

biochemistry↗

bioRxiv2017

Molecular Basis For The Specific And Multivariate Recognitions Of RNA Substrates By Human hnRNPA2/B1

Human hnRNPA2/B1 is an RNA-binding protein that plays important roles in a variety of biological processes, from mRNA maturation, trafficking and translation to regulation of gene expression mediated by long non-coding RNAs and microRNAs. hnRNPA2/B1 contains two RNA recognition motifs (RRM) that provide sequence-specific recognition of widespread RNA substrates including recently reported m6A-containing motifs. Here we determined the first crystal structures of tandem RRM domains of hnRNPA2/B1 in complex with various RNA substrates. Our structures reveal that hnRNPA2/B1 can bind two RNA elements in an antiparallel fashion with a sequence preference for AGG and UAG by RRM1 and RRM2, respectively, suggesting an RNA matchmaker mechanism during the hnRNPA2/B1 function. However, our combined studies did not observe specific binding of m6A by either the RRM domains or the full-length hnRNPA2/B1, implying that the \"reader\" function of hnRNPA2/B1 may adopt an unknown mechanism that remains to be characterized.

biochemistry↗

bioRxiv2017

Recording action potential propagation in single axons using multi-electrode arrays

The small caliber of central nervous system (CNS) axons makes routine study of axonal physiology relatively difficult. However, while recording extracellular action potentials from neurons cultured on planer multi-electrode arrays (MEAs) we found activity among groups of electrodes consistent with action potential propagation in single neurons. Action potential propagation was evident as widespread, repetitive cooccurrence of extracellular action potentials (eAPs) among groups of electrodes. These eAPs occurred with invariant sequences and inter-electrode latencies that were consistent with reported measures of action potential propagation in unmyelinated axons. Within co-active electrode groups, the inter-electrode eAP latencies were temperature sensitive, as expected for action potential propagation. Our data are consistent with these signals primarily reflecting axonal action potential propagation, from axons with a high density of voltage-gated sodium channels. Repeated codetection of eAPs by multiple electrodes confirmed these eAPs are from individual neurons and averaging these eAPs revealed sub-threshold events at other electrodes. The sequence of electrodes at which eAPs co-occur uniquely identifies these neurons, allowing us to monitor spiking of single identified neurons within neuronal ensembles. We recorded dynamic changes in single axon physiology such as simultaneous increases and decreases in excitability in different portions of single axonal arbors over several hours. Over several weeks, we measured changes in inter-electrode propagation latencies and ongoing changes in excitability in different regions of single axonal arbors. We recorded action potential propagation signals in human induced pluripotent stem cell-derived neurons which could thus be used to study axonal physiology in human disease models.\n\nSignificance StatementStudying the physiology of central nervous system axons is limited by the technical challenges of recording from axons with pairs of patch or extracellular electrodes at two places along single axons. We studied action potential propagation in single axonal arbors with extracellular recording with multi-electrode arrays. These recordings were non-invasive and were done from several sites of small caliber axons and branches. Unlike conventional extracellular recording, we unambiguously identified and labelled the neuronal source of propagating action potentials. We manipulated and quantified action potential propagation and found a surprisingly high density of axonal voltage-gated sodium channels. Our experiments also demonstrate that the excitability of different portions of axonal arbors can be independently regulated on time scales from hours to weeks.

neuroscience↗

bioRxiv2017

Single-cell epigenomics maps the continuous regulatory landscape of human hematopoietic differentiation

AbstractNormal human hematopoiesis involves cellular differentiation of multipotent cells into progressively more lineage-restricted states. While epigenomic landscapes of this process have been explored in immunophenotypically-defined populations, the single-cell regulatory variation that defines hematopoietic differentiation has been hidden by ensemble averaging. We generated single-cell chromatin accessibility landscapes across 8 populations of immunophenotypically-defined human hematopoietic cell types. Using bulk chromatin accessibility profiles to scaffold our single-cell data analysis, we constructed an epigenomic landscape of human hematopoiesis and characterized epigenomic heterogeneity within phenotypically sorted populations to find epigenomic lineage-bias toward different developmental branches in multipotent stem cell states. We identify and isolate sub-populations within classically-defined granulocyte-macrophage progenitors (GMPs) and use ATAC-seq and RNA-seq to confirm that GMPs are epigenomically and transcriptomically heterogeneous. Furthermore, we identified transcription factors and cis-regulatory elements linked to changes in chromatin accessibility within cellular populations and across a continuous myeloid developmental trajectory, and observe relatively simple TF motif dynamics give rise to a broad diversity of accessibility dynamics at cis-regulatory elements. Overall, this work provides a template for exploration of complex regulatory dynamics in primary human tissues at the ultimate level of granular specificity - the single cell.\n\nOne Sentence SummarySingle cell chromatin accessibility reveals a high-resolution, continuous landscape of regulatory variation in human hematopoiesis.

genomics↗

bioRxiv2017

chromVAR: Inferring transcription factor variation from single-cell epigenomic data

Single cell ATAC-seq (scATAC) yields sparse data that makes application of conventional computational approaches for data analysis challenging or impossible. We developed chromVAR, an R package for analyzing sparse chromatin accessibility data by estimating the gain or loss of accessibility within sets of peaks sharing the same motif or annotation while controlling for known technical biases. chromVAR enables accurate clustering of scATAC-seq profiles and enables characterization of known, or the de novo identification of novel, sequence motifs associated with variation in chromatin accessibility across single cells or other sparse epigenomic data sets.

bioinformatics↗

bioRxiv2017

Cyclic-di-GMP is required for corneal infection by Pseudomonas aeruginosa and modulates host immunity

Biofilms are extremely tolerant toward antimicrobial treatment and host immune clearance due to their distinct physiology and protection by extracellular polymeric substances. Bis-(3{acute}-5{acute})-cyclic dimeric guanosine monophosphate (c-di-GMP) is an essential messenger that regulates biofilm formation by a wide range of bacteria. However, there is a lack of physiological characterization of biofilms in vivo as well as the roles of c-di-GMP signaling in mediating host-biofilm interactions. Here, we employed dual RNA-Seq to characterize the host and pathogen transcriptomes during Pseudomonas aeruginosa infection using a mouse keratitis model. In vivo P. aeruginosa biofilms maintained a distinct physiology compared with in vitro P. aeruginosa biofilms, with enhanced virulence and iron uptake capacity. C-di-GMP synthesis was enhanced in P. aeruginosa cells in vivo, potentially due to down-regulation of the expression of several phosphodiesterases (e.g., DipA, NbdA). Increased intracellular c-di-GMP levels were required for long-term ocular colonization of P. aeruginosa and impaired host innate immunity.

microbiology↗