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1.
Proc Natl Acad Sci U S A ; 109(10): E595-604, 2012 Mar 06.
Artículo en Inglés | MEDLINE | ID: mdl-22343529

RESUMEN

The regulation of cell shape is a common challenge faced by organisms across all biological kingdoms. In nearly all bacteria, cell shape is determined by the architecture of the peptidoglycan cell wall, a macromolecule consisting of glycan strands crosslinked by peptides. In addition to shape, cell growth must also maintain the wall structural integrity to prevent lysis due to large turgor pressures. Robustness can be accomplished by establishing a globally ordered cell-wall network, although how a bacterium generates and maintains peptidoglycan order on the micron scale using nanometer-sized proteins remains a mystery. Here, we demonstrate that left-handed chirality of the MreB cytoskeleton in the rod-shaped bacterium Escherichia coli gives rise to a global, right-handed chiral ordering of the cell wall. Local, MreB-guided insertion of material into the peptidoglycan network naturally orders the glycan strands and causes cells to twist left-handedly during elongational growth. Through comparison with the right-handed twisting of Bacillus subtilis cells, our work supports a common mechanism linking helical insertion and chiral cell-wall ordering in rod-shaped bacteria. These physical principles of cell growth link the molecular structure of the bacterial cytoskeleton, mechanisms of wall synthesis, and the coordination of cell-wall architecture.


Asunto(s)
Pared Celular/metabolismo , Proteínas de Escherichia coli/metabolismo , Peptidoglicano/química , Bacillus subtilis/metabolismo , Proteínas Bacterianas/química , Biofisica/métodos , Biología Computacional/métodos , Citoesqueleto/metabolismo , Escherichia coli/metabolismo , Presión Osmótica , Péptidos/química , Polisacáridos/química
2.
Proc Natl Acad Sci U S A ; 108(38): 15822-7, 2011 Sep 20.
Artículo en Inglés | MEDLINE | ID: mdl-21903929

RESUMEN

Bacterial cells possess multiple cytoskeletal proteins involved in a wide range of cellular processes. These cytoskeletal proteins are dynamic, but the driving forces and cellular functions of these dynamics remain poorly understood. Eukaryotic cytoskeletal dynamics are often driven by motor proteins, but in bacteria no motors that drive cytoskeletal motion have been identified to date. Here, we quantitatively study the dynamics of the Escherichia coli actin homolog MreB, which is essential for the maintenance of rod-like cell shape in bacteria. We find that MreB rotates around the long axis of the cell in a persistent manner. Whereas previous studies have suggested that MreB dynamics are driven by its own polymerization, we show that MreB rotation does not depend on its own polymerization but rather requires the assembly of the peptidoglycan cell wall. The cell-wall synthesis machinery thus either constitutes a novel type of extracellular motor that exerts force on cytoplasmic MreB, or is indirectly required for an as-yet-unidentified motor. Biophysical simulations suggest that one function of MreB rotation is to ensure a uniform distribution of new peptidoglycan insertion sites, a necessary condition to maintain rod shape during growth. These findings both broaden the view of cytoskeletal motors and deepen our understanding of the physical basis of bacterial morphogenesis.


Asunto(s)
Actinas/metabolismo , Pared Celular/metabolismo , Proteínas de Escherichia coli/metabolismo , Escherichia coli/metabolismo , Actinas/genética , Amdinocilina/farmacología , Antibacterianos/farmacología , Simulación por Computador , Depsipéptidos/farmacología , Relación Dosis-Respuesta a Droga , Proteínas de Escherichia coli/genética , Glicosilación , Cinética , Proteínas Luminiscentes/genética , Proteínas Luminiscentes/metabolismo , Microscopía Fluorescente , Modelos Biológicos , Péptidos/metabolismo , Peptidoglicano/metabolismo , Rotación , Vancomicina/farmacología
3.
Mol Microbiol ; 81(2): 340-53, 2011 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-21501250

RESUMEN

For the rod-shaped Gram-negative bacterium Escherichia coli, changes in cell shape have critical consequences for motility, immune system evasion, proliferation and adhesion. For most bacteria, the peptidoglycan cell wall is both necessary and sufficient to determine cell shape. However, how the synthesis machinery assembles a peptidoglycan network with a robustly maintained micron-scale shape has remained elusive. To explore shape maintenance, we have quantified the robustness of cell shape in three Gram-negative bacteria in different genetic backgrounds and in the presence of an antibiotic that inhibits division. Building on previous modelling suggesting a prominent role for mechanical forces in shape regulation, we introduce a biophysical model for the growth dynamics of rod-shaped cells to investigate the roles of spatial regulation of peptidoglycan synthesis, glycan-strand biochemistry and mechanical stretching during insertion. Our studies reveal that rod-shape maintenance requires insertion to be insensitive to fluctuations in cell-wall density and stress, and even a simple helical pattern of insertion is sufficient for over sixfold elongation without significant loss in shape. In addition, we demonstrate that both the length and pre-stretching of newly inserted strands regulate cell width. In sum, we show that simple physical rules can allow bacteria to achieve robust, shape-preserving cell-wall growth.


Asunto(s)
Pared Celular/metabolismo , Escherichia coli/citología , Peptidoglicano/metabolismo , Pseudomonas aeruginosa/citología , Salmonella typhimurium/citología , Antibacterianos/metabolismo , Escherichia coli/efectos de los fármacos , Escherichia coli/metabolismo , Microscopía , Modelos Moleculares , Pseudomonas aeruginosa/efectos de los fármacos , Pseudomonas aeruginosa/metabolismo , Salmonella typhimurium/efectos de los fármacos , Salmonella typhimurium/metabolismo
4.
Front Cardiovasc Med ; 9: 960419, 2022.
Artículo en Inglés | MEDLINE | ID: mdl-36684605

RESUMEN

Introduction: We sought to explore biomarkers of coronary atherosclerosis in an unbiased fashion. Methods: We analyzed 665 patients (mean ± SD age, 56 ± 11 years; 47% male) from the GLOBAL clinical study (NCT01738828). Cases were defined by the presence of any discernable atherosclerotic plaque based on comprehensive cardiac computed tomography (CT). De novo Bayesian networks built out of 37,000 molecular measurements and 99 conventional biomarkers per patient examined the potential causality of specific biomarkers. Results: Most highly ranked biomarkers by gradient boosting were interleukin-6, symmetric dimethylarginine, LDL-triglycerides [LDL-TG], apolipoprotein B48, palmitoleic acid, small dense LDL, alkaline phosphatase, and asymmetric dimethylarginine. In Bayesian analysis, LDL-TG was directly linked to atherosclerosis in over 95% of the ensembles. Genetic variants in the genomic region encoding hepatic lipase (LIPC) were associated with LIPC gene expression, LDL-TG levels and with atherosclerosis. Discussion: Triglyceride-rich LDL particles, which can now be routinely measured with a direct homogenous assay, may play an important role in atherosclerosis development. Clinical trial registration: GLOBAL clinical study (Genetic Loci and the Burden of Atherosclerotic Lesions); [https://clinicaltrials.gov/ct2/show/NCT01738828?term=NCT01738828&rank=1], identifier [NCT01738828].

5.
Biophys J ; 96(10): 3926-35, 2009 May 20.
Artículo en Inglés | MEDLINE | ID: mdl-19450465

RESUMEN

The network of interactions underlying liver regeneration is robust and precise with liver resections resulting in controlled hyperplasia (cell proliferation) that terminates when the liver regains its lost mass. The interplay of cytokines and growth factors responsible for the inception and termination of this hyperplasia is not well understood. A model is developed for this network of interactions based on the known data of liver resections. This model reproduces the relevant published data on liver regeneration and provides geometric insights into the experimental observations. The predictions of this model are used to suggest two novel strategies for speeding up liver mass recovery and a strategy for enabling liver mass recovery in cases where a resection leaves <20% of the liver that would otherwise result in complete loss of liver mass.


Asunto(s)
Regeneración Hepática , Modelos Biológicos , Hepatectomía , Hígado/metabolismo , Hígado/patología , Mutación , Tamaño de los Órganos , Factores de Tiempo
6.
Phys Rev Lett ; 103(26): 268102, 2009 Dec 31.
Artículo en Inglés | MEDLINE | ID: mdl-20366348

RESUMEN

Time-dependent external perturbations provide powerful probes of the function of molecular machines. Here we study biological proton pumping in an oscillating electric field. The protein cytochrome c oxidase is the main energy transducer in aerobic life, converting chemical energy into an electric potential by pumping protons across a membrane. With the help of master-equation descriptions that recover the key thermodynamic and kinetic properties of this biological "fuel cell," we show that the proton pumping efficiency and the electronic currents in steady state depend significantly on the frequency and amplitude of the applied field, allowing us to distinguish between different microscopic mechanisms of the machine. A spectral analysis reveals dominant reaction steps consistent with an electron-gated pumping mechanism.


Asunto(s)
Electricidad , Bombas de Protones/metabolismo , Complejo IV de Transporte de Electrones/metabolismo , Electrones , Modelos Biológicos
7.
Elife ; 62017 03 15.
Artículo en Inglés | MEDLINE | ID: mdl-28296636

RESUMEN

Computational analysis of gene expression to determine both the sequence of lineage choices made by multipotent cells and to identify the genes influencing these decisions is challenging. Here we discover a pattern in the expression levels of a sparse subset of genes among cell types in B- and T-cell developmental lineages that correlates with developmental topologies. We develop a statistical framework using this pattern to simultaneously infer lineage transitions and the genes that determine these relationships. We use this technique to reconstruct the early hematopoietic and intestinal developmental trees. We extend this framework to analyze single-cell RNA-seq data from early human cortical development, inferring a neocortical-hindbrain split in early progenitor cells and the key genes that could control this lineage decision. Our work allows us to simultaneously infer both the identity and lineage of cell types as well as a small set of key genes whose expression patterns reflect these relationships.


Asunto(s)
Diferenciación Celular , Linaje de la Célula , Biología Computacional/métodos , Perfilación de la Expresión Génica , Regulación del Desarrollo de la Expresión Génica , Transcripción Genética , Humanos
8.
Elife ; 62017 03 15.
Artículo en Inglés | MEDLINE | ID: mdl-28296635

RESUMEN

The complexity of gene regulatory networks that lead multipotent cells to acquire different cell fates makes a quantitative understanding of differentiation challenging. Using a statistical framework to analyze single-cell transcriptomics data, we infer the gene expression dynamics of early mouse embryonic stem (mES) cell differentiation, uncovering discrete transitions across nine cell states. We validate the predicted transitions across discrete states using flow cytometry. Moreover, using live-cell microscopy, we show that individual cells undergo abrupt transitions from a naïve to primed pluripotent state. Using the inferred discrete cell states to build a probabilistic model for the underlying gene regulatory network, we further predict and experimentally verify that these states have unique response to perturbations, thus defining them functionally. Our study provides a framework to infer the dynamics of differentiation from single cell transcriptomics data and to build predictive models of the gene regulatory networks that drive the sequence of cell fate decisions during development.


Asunto(s)
Diferenciación Celular , Células Madre Embrionarias/fisiología , Animales , Citometría de Flujo , Perfilación de la Expresión Génica , Ratones , Análisis de la Célula Individual
9.
Cell Stem Cell ; 20(1): 120-134, 2017 01 05.
Artículo en Inglés | MEDLINE | ID: mdl-28094016

RESUMEN

During human brain development, multiple signaling pathways generate diverse cell types with varied regional identities. Here, we integrate single-cell RNA sequencing and clonal analyses to reveal lineage trees and molecular signals underlying early forebrain and mid/hindbrain cell differentiation from human embryonic stem cells (hESCs). Clustering single-cell transcriptomic data identified 41 distinct populations of progenitor, neuronal, and non-neural cells across our differentiation time course. Comparisons with primary mouse and human gene expression data demonstrated rostral and caudal progenitor and neuronal identities from early brain development. Bayesian analyses inferred a unified cell-type lineage tree that bifurcates between cortical and mid/hindbrain cell types. Two methods of clonal analyses confirmed these findings and further revealed the importance of Wnt/ß-catenin signaling in controlling this lineage decision. Together, these findings provide a rich transcriptome-based lineage map for studying human brain development and modeling developmental disorders.


Asunto(s)
Encéfalo/embriología , Linaje de la Célula , Desarrollo Embrionario , Células Madre Embrionarias Humanas/citología , Análisis de la Célula Individual/métodos , Animales , Encéfalo/metabolismo , Línea Celular , Linaje de la Célula/genética , Células Clonales , Desarrollo Embrionario/genética , Humanos , Ratones , Modelos Biológicos , Neuronas/citología , Neuronas/metabolismo , Reproducibilidad de los Resultados , Análisis de Secuencia de ARN , Factores de Transcripción/metabolismo , Transcriptoma/genética , Vía de Señalización Wnt/genética
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