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Recent Publications

An efficient KRAB domain for CRISPRi applications in human cells.

An efficient KRAB domain for CRISPRi applications in human cells.

Nat Methods. 2020 Oct 05;:

Authors: Alerasool N, Segal D, Lee H, Taipale M

Abstract
Clustered regularly interspaced short palindromic repeat interference (CRISPRi), based on the fusion of inactive Cas9 (dCas9) to the Krüppel-associated box (KRAB) repressor, is a powerful platform for silencing gene expression. However, it suffers from incomplete silencing of target genes. We assayed 57 KRAB domains for their repressive potency and identified the ZIM3 KRAB domain as an exceptionally potent repressor. We establish that ZIM3 KRAB-dCas9 fusion silences gene expression more efficiently than existing platforms.

PMID: 33020655 [PubMed - as supplied by publisher]



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Constraint-induced movement therapy promotes motor recovery after neonatal stroke in the absence of neural precursor activation.

Constraint-induced movement therapy promotes motor recovery after neonatal stroke in the absence of neural precursor activation.

Eur J Neurosci. 2020 Oct 03;:

Authors: Adams KV, Mahmud N, Green-Holland M, Vonderwalde I, Umebayashi D, Sachewsky N, Coles BL, van der Kooy D, Morshead CM

Abstract
Neonatal stroke is a leading cause of long-term disability and currently available rehabilitation treatments are insufficient to promote recovery. Activating neural precursor cells (NPCs) in adult rodents, in combination with rehabilitation, can accelerate functional recovery following stroke. Here, we describe a novel method of constraint-induced movement therapy (CIMT) in a rodent model of neonatal stroke that leads to improved functional outcomes, and asked whether the recovery was correlated with expansion of NPCs. A hypoxia/ischemia (H/I) injury was induced on postnatal day 8 (PND8) via unilateral carotid artery ligation followed by systemic hypoxia. One week and two weeks post-H/I, CIMT was administered in the form of 3 botulinum toxin (Botox) injections, which induced temporary paralysis in the unaffected limb. Functional recovery was assessed using the foot fault task. NPC proliferation was assessed using the neurosphere assay and EdU immunohistochemistry. We found that neonatal H/I injury alone expands the NPC pool by >2.5 fold relative to controls. We determined that Botox injections as a means to provide CIMT results in significant functional motor recovery following H/I. However, CIMT does not lead to enhanced NPC activation or migration into the injured parenchyma in vivo. At the time of functional recovery increased numbers of proliferating inflammatory cells were found within the injured motor cortex. Together, these findings suggest that NPC activation following CIMT does not account for the observed functional improvement and suggests that CIMT-mediated modification of the CNS inflammatory response may play a role in the motor recovery.

PMID: 33010080 [PubMed - as supplied by publisher]



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Fast and Flexible Protein Design Using Deep Graph Neural Networks.

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Fast and Flexible Protein Design Using Deep Graph Neural Networks.

Cell Syst. 2020 Sep 15;:

Authors: Strokach A, Becerra D, Corbi-Verge C, Perez-Riba A, Kim PM

Abstract
Protein structure and function is determined by the arrangement of the linear sequence of amino acids in 3D space. We show that a deep graph neural network, ProteinSolver, can precisely design sequences that fold into a predetermined shape by phrasing this challenge as a constraint satisfaction problem (CSP), akin to Sudoku puzzles. We trained ProteinSolver on over 70,000,000 real protein sequences corresponding to over 80,000 structures. We show that our method rapidly designs new protein sequences and benchmark them in silico using energy-based scores, molecular dynamics, and structure prediction methods. As a proof-of-principle validation, we use ProteinSolver to generate sequences that match the structure of serum albumin, then synthesize the top-scoring design and validate it in vitro using circular dichroism. ProteinSolver is freely available at http://design.proteinsolver.org and https://gitlab.com/ostrokach/proteinsolver. A record of this paper's transparent peer review process is included in the Supplemental Information.

PMID: 32971019 [PubMed - as supplied by publisher]



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Parental Bias Has Benefits.

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Parental Bias Has Benefits.

Neuron. 2020 09 23;107(6):994-996

Authors: DeVeale B, van der Kooy D

Abstract
In this issue, Laukoter et al., 2020 report that parent-of-origin-dependent expression is homogeneous across distinct cortical cell types and within individual populations. Conversely, they observe preferential sensitivity of astrocytes to altered doses of imprinted loci.

PMID: 32971001 [PubMed - indexed for MEDLINE]



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Functional genomic landscape of cancer-intrinsic evasion of killing by T cells.

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Functional genomic landscape of cancer-intrinsic evasion of killing by T cells.

Nature. 2020 10;586(7827):120-126

Authors: Lawson KA, Sousa CM, Zhang X, Kim E, Akthar R, Caumanns JJ, Yao Y, Mikolajewicz N, Ross C, Brown KR, Zid AA, Fan ZP, Hui S, Krall JA, Simons DM, Slater CJ, De Jesus V, Tang L, Singh R, Goldford JE, Martin S, Huang Q, Francis EA, Habsid A, Climie R, Tieu D, Wei J, Li R, Tong AHY, Aregger M, Chan KS, Han H, Wang X, Mero P, Brumell JH, Finelli A, Ailles L, Bader G, Smolen GA, Kingsbury GA, Hart T, Kung C, Moffat J

Abstract
The genetic circuits that allow cancer cells to evade destruction by the host immune system remain poorly understood1-3. Here, to identify a phenotypically robust core set of genes and pathways that enable cancer cells to evade killing mediated by cytotoxic T lymphocytes (CTLs), we performed genome-wide CRISPR screens across a panel of genetically diverse mouse cancer cell lines that were cultured in the presence of CTLs. We identify a core set of 182 genes across these mouse cancer models, the individual perturbation of which increases either the sensitivity or the resistance of cancer cells to CTL-mediated toxicity. Systematic exploration of our dataset using genetic co-similarity reveals the hierarchical and coordinated manner in which genes and pathways act in cancer cells to orchestrate their evasion of CTLs, and shows that discrete functional modules that control the interferon response and tumour necrosis factor (TNF)-induced cytotoxicity are dominant sub-phenotypes. Our data establish a central role for genes that were previously identified as negative regulators of the type-II interferon response (for example, Ptpn2, Socs1 and Adar1) in mediating CTL evasion, and show that the lipid-droplet-related gene Fitm2 is required for maintaining cell fitness after exposure to interferon-γ (IFNγ). In addition, we identify the autophagy pathway as a conserved mediator of the evasion of CTLs by cancer cells, and show that this pathway is required to resist cytotoxicity induced by the cytokines IFNγ and TNF. Through the mapping of cytokine- and CTL-based genetic interactions, together with in vivo CRISPR screens, we show how the pleiotropic effects of autophagy control cancer-cell-intrinsic evasion of killing by CTLs and we highlight the importance of these effects within the tumour microenvironment. Collectively, these data expand our knowledge of the genetic circuits that are involved in the evasion of the immune system by cancer cells, and highlight genetic interactions that contribute to phenotypes associated with escape from killing by CTLs.

PMID: 32968282 [PubMed - indexed for MEDLINE]



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Systematic analysis of bypass suppression of essential genes.

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Systematic analysis of bypass suppression of essential genes.

Mol Syst Biol. 2020 Sep;16(9):e9828

Authors: van Leeuwen J, Pons C, Tan G, Wang JZ, Hou J, Weile J, Gebbia M, Liang W, Shuteriqi E, Li Z, Lopes M, Ušaj M, Dos Santos Lopes A, van Lieshout N, Myers CL, Roth FP, Aloy P, Andrews BJ, Boone C

Abstract
Essential genes tend to be highly conserved across eukaryotes, but, in some cases, their critical roles can be bypassed through genetic rewiring. From a systematic analysis of 728 different essential yeast genes, we discovered that 124 (17%) were dispensable essential genes. Through whole-genome sequencing and detailed genetic analysis, we investigated the genetic interactions and genome alterations underlying bypass suppression. Dispensable essential genes often had paralogs, were enriched for genes encoding membrane-associated proteins, and were depleted for members of protein complexes. Functionally related genes frequently drove the bypass suppression interactions. These gene properties were predictive of essential gene dispensability and of specific suppressors among hundreds of genes on aneuploid chromosomes. Our findings identify yeast's core essential gene set and reveal that the properties of dispensable essential genes are conserved from yeast to human cells, correlating with human genes that display cell line-specific essentiality in the Cancer Dependency Map (DepMap) project.

PMID: 32939983 [PubMed - in process]



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Reengineering biocatalysts: Computational redesign of chondroitinase ABC improves efficacy and stability.

Reengineering biocatalysts: Computational redesign of chondroitinase ABC improves efficacy and stability.

Sci Adv. 2020 Aug;6(34):

Authors: Hettiaratchi MH, O'Meara MJ, O'Meara TR, Pickering AJ, Letko-Khait N, Shoichet MS

Abstract
Maintaining biocatalyst stability and activity is a critical challenge. Chondroitinase ABC (ChABC) has shown promise in central nervous system (CNS) regeneration, yet its therapeutic utility is severely limited by instability. We computationally reengineered ChABC by introducing 37, 55, and 92 amino acid changes using consensus design and forcefield-based optimization. All mutants were more stable than wild-type ChABC with increased aggregation temperatures between 4° and 8°C. Only ChABC with 37 mutations (ChABC-37) was more active and had a 6.5 times greater half-life than wild-type ChABC, increasing to 106 hours (4.4 days) from only 16.8 hours. ChABC-37, expressed as a fusion protein with Src homology 3 (ChABC-37-SH3), was active for 7 days when released from a hydrogel modified with SH3-binding peptides. This study demonstrates the broad opportunity to improve biocatalysts through computational engineering and sets the stage for future testing of this substantially improved protein in the treatment of debilitating CNS injuries.

PMID: 32937356 [PubMed - as supplied by publisher]



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TheCellVision.org: A Database for Visualizing and Mining High-Content Cell Imaging Projects.

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TheCellVision.org: A Database for Visualizing and Mining High-Content Cell Imaging Projects.

G3 (Bethesda). 2020 Sep 15;:

Authors: Masinas MPD, Mattiazzi Usaj M, Usaj M, Boone C, Andrews BJ

Abstract
Advances in genome engineering and high throughput imaging technologies have enabled genome- scale screens of single cells for a variety of phenotypes, including subcellular morphology and protein localization. We constructed TheCellVision.org, a freely available and web-accessible image visualization and data browsing tool that serves as a central repository for fluorescence microscopy images and associated quantitative data produced by high-content screening experiments. Currently, TheCellVision.org hosts ~575,590 images and associated analysis results from two published high- content screening (HCS) projects focused on the budding yeast Saccharomyces cerevisiae TheCellVision.org allows users to access, visualize and explore fluorescence microscopy images, and to search, compare, and extract data related to subcellular compartment morphology, protein abundance, and localization. Each dataset can be queried independently or as part of a search across multiple datasets using the advanced search option. The website also hosts computational tools associated with the available datasets, which can be applied to other projects and cell systems, a feature we demonstrate using published images of mammalian cells. Providing access to HCS data through websites such as TheCelllVision.org enables new discovery and independent re-analyses of imaging data.

PMID: 32934016 [PubMed - as supplied by publisher]



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Attenuated diphtheria toxin mediates siRNA delivery.

Attenuated diphtheria toxin mediates siRNA delivery.

Sci Adv. 2020 May;6(18):

Authors: Arnold AE, Smith LJ, Beilhartz GL, Bahlmann LC, Jameson E, Melnyk RA, Shoichet MS

Abstract
Toxins efficiently deliver cargo to cells by binding to cell surface ligands, initiating endocytosis, and escaping the endolysosomal pathway into the cytoplasm. We took advantage of this delivery pathway by conjugating an attenuated diphtheria toxin to siRNA, thereby achieving gene downregulation in patient-derived glioblastoma cells. We delivered siRNA against integrin-β1 (ITGB1)-a gene that promotes invasion and metastasis-and siRNA against eukaryotic translation initiation factor 3 subunit b (eIF-3b)-a survival gene. We demonstrated mRNA downregulation of both genes and the corresponding functional outcomes: knockdown of ITGB1 led to a significant inhibition of invasion, shown with an innovative 3D hydrogel model; and knockdown of eIF-3b resulted in significant cell death. This is the first example of diphtheria toxin being used to deliver siRNAs, and the first time a toxin-based siRNA delivery strategy has been shown to induce relevant genotypic and phenotypic effects in cancer cells.

PMID: 32917630 [PubMed - as supplied by publisher]



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Tempora: Cell trajectory inference using time-series single-cell RNA sequencing data.

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Tempora: Cell trajectory inference using time-series single-cell RNA sequencing data.

PLoS Comput Biol. 2020 09;16(9):e1008205

Authors: Tran TN, Bader GD

Abstract
Single-cell RNA sequencing (scRNA-seq) can map cell types, states and transitions during dynamic biological processes such as tissue development and regeneration. Many trajectory inference methods have been developed to order cells by their progression through a dynamic process. However, when time series data is available, most of these methods do not consider the available time information when ordering cells and are instead designed to work only on a single scRNA-seq data snapshot. We present Tempora, a novel cell trajectory inference method that orders cells using time information from time-series scRNA-seq data. In performance comparison tests, Tempora inferred known developmental lineages from three diverse tissue development time series data sets, beating state of the art methods in accuracy and speed. Tempora works at the level of cell clusters (types) and uses biological pathway information to help identify cell type relationships. This approach increases gene expression signal from single cells, processing speed, and interpretability of the inferred trajectory. Our results demonstrate the utility of a combination of time and pathway information to supervise trajectory inference for scRNA-seq based analysis.

PMID: 32903255 [PubMed - indexed for MEDLINE]



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