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1.
Opt Lett ; 37(3): 440-2, 2012 Feb 01.
Artículo en Inglés | MEDLINE | ID: mdl-22297379

RESUMEN

Using oscillating optical tweezers, we show that controlled alignment of rod-shaped bacterial cells allows imaging fluorescently labeled three-dimensional (3D) subcellular structures from different, optimized viewpoints. To illustrate our method, we analyze the Z ring of E. coli. We obtain that the radial width of the Z ring in unconstricted cells is about 120 nm. This result suggests that the Z ring consists of an extremely sparse network of FtsZ filaments.


Asunto(s)
Escherichia coli/citología , Imagenología Tridimensional/métodos , Espacio Intracelular , Pinzas Ópticas
2.
Phys Biol ; 8(6): 066003, 2011 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-22015938

RESUMEN

Bacterial cell division takes place in three phases: Z-ring formation at midcell, followed by divisome assembly and building of the septum per se. Using time-lapse microscopy of live bacteria and a high-precision cell edge detection method, we have previously found the true time for the onset of septation, τ(c), and the time between consecutive divisions, τ(g). Here, we combine the above method with measuring the dynamics of the FtsZ-GFP distribution in individual Escherichia coli cells to determine the Z-ring positioning time, τ(z). To analyze the FtsZ-GFP distribution along the cell, we used the integral fluorescence profile (IFP), which was obtained by integrating the fluorescence intensity across the cell width. We showed that the IFP may be approximated by an exponential peak and followed the peak evolution throughout the cell cycle, to find a quantitative criterion for the positioning of the Z-ring and hence the value of τ(z). We defined τ(z) as the transition from oscillatory to stable behavior of the mean IFP position. This criterion was corroborated by comparison of the experimental results to a theoretical model for the FtsZ dynamics, driven by Min oscillations. We found that τ(z) < τ(c) for all the cells that were analyzed. Moreover, our data suggested that τ(z) is independent of τ(c), τ(g) and the cell length at birth, L(0). These results are consistent with the current understanding of the Z-ring positioning and cell septation processes.


Asunto(s)
Escherichia coli/citología , Proteínas Bacterianas/análisis , Ciclo Celular , Proteínas del Citoesqueleto/análisis , Proteínas Fluorescentes Verdes/análisis , Microscopía Fluorescente/métodos
3.
J Med Genet ; 48(5): 290-8, 2011 May.
Artículo en Inglés | MEDLINE | ID: mdl-21343628

RESUMEN

Recurrent deletions of 2q32q33 have recently been reported as a new microdeletion syndrome, clinical features of which include significant learning difficulties, growth retardation, dysmorphic features, thin and sparse hair, feeding difficulties, and cleft or high palate. Haploinsufficiency of one gene within the deleted region, SATB2, has been suggested to be responsible for most of the features of the syndrome. This article describes seven previously unreported patients with deletions at 2q33.1, all partially overlapping the previously described critical region for the 2q33.1 microdeletion syndrome. The deletions ranged in size from 35 kb to 10.4 Mb, with the smallest deletion entirely within the SATB2 gene. Patients demonstrated significant developmental delay and challenging behaviour, a particular behavioural phenotype that seems to be emerging with more reported patients with this condition. One patient in this cohort has a deletion entirely within SATB2 and has a cleft palate, whereas several patients with larger deletions have a high arched palate. In addition, one other patient has significant orthopaedic problems with ligamentous laxity. Interestingly, this patient has a deletion that lies just distal to SATB2. The orthopaedic problems have not been reported previously and are possibly an additional feature of this syndrome. Overall, this report provides further evidence that the SATB2 gene is the critical gene in this microdeletion syndrome. In addition, because the individuals in this study range in age from 3-19 years, these patients will help define the natural progression of the phenotype in patients with this microdeletion.


Asunto(s)
Deleción Cromosómica , Trastornos de los Cromosomas/genética , Cromosomas Humanos Par 2/genética , Fenotipo , Adolescente , Niño , Preescolar , Hibridación Genómica Comparativa , Femenino , Humanos , Hibridación Fluorescente in Situ , Masculino , Proteínas de Unión a la Región de Fijación a la Matriz/genética , Síndrome , Factores de Transcripción/genética , Adulto Joven
4.
Opt Lett ; 36(1): 40-2, 2011 Jan 01.
Artículo en Inglés | MEDLINE | ID: mdl-21209680

RESUMEN

Using a single-beam, oscillating optical tweezers, we demonstrate trapping and rotation of rod-shaped bacterial cells with respect to the optical axis. The angle of rotation, θ, is determined by the amplitude of the oscillation. It is shown that θ can be measured from the longitudinal cell intensity profiles in the corresponding phase-contrast images. The technique allows viewing the cell from different perspectives and can provide a useful tool in fluorescence microscopy for the analysis of three-dimensional subcellular structures.


Asunto(s)
Escherichia coli/citología , Fenómenos Ópticos , Pinzas Ópticas , Rotación , Distribución Normal
5.
Phys Biol ; 5(4): 046001, 2008 Nov 07.
Artículo en Inglés | MEDLINE | ID: mdl-18997273

RESUMEN

We monitor the shape dynamics of individual E. coli cells using time-lapse microscopy together with accurate image analysis. This allows measuring the dynamics of single-cell parameters throughout the cell cycle. In previous work, we have used this approach to characterize the main features of single-cell morphogenesis between successive divisions. Here, we focus on the behavior of the parameters that are related to cell division and study their variation over a population of 30 cells. In particular, we show that the single-cell data for the constriction width dynamics collapse onto a unique curve following appropriate rescaling of the corresponding variables. This suggests the presence of an underlying time scale that determines the rate at which the cell cycle advances in each individual cell. For the case of cell length dynamics a similar rescaling of variables emphasizes the presence of a breakpoint in the growth rate at the time when division starts, tau(c). We also find that the tau(c) of individual cells is correlated with their generation time, tau(g), and inversely correlated with the corresponding length at birth, L(0). Moreover, the extent of the T-period, tau(g) - tau(c), is apparently independent of tau(g). The relations between tau(c), tau(g) and L(0) indicate possible compensation mechanisms that maintain cell length variability at about 10%. Similar behavior was observed for both fast-growing cells in a rich medium (LB) and for slower growth in a minimal medium (M9-glucose). To reveal the molecular mechanisms that lead to the observed organization of the cell cycle, we should further extend our approach to monitor the formation of the divisome.


Asunto(s)
División Celular , Escherichia coli K12/citología , Escherichia coli K12/crecimiento & desarrollo , Escherichia coli K12/ultraestructura , Modelos Biológicos , Factores de Tiempo
6.
Phys Rev E Stat Nonlin Soft Matter Phys ; 77(6 Pt 1): 061902, 2008 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-18643295

RESUMEN

The shape of Escherichia coli is approximately that of a cylinder with hemispherical caps. Since its size is not much larger than optical resolution, it has been difficult to quantify deviations from this approximation. We show that one can bypass this limitation and obtain the cell shape with subpixel accuracy. The resulting contours are shown to deviate from the hemisphere-cylinder-hemisphere shape. In particular, the cell is weakly asymmetric. Its two caps are different from each other and the sides are slightly curved. Most cells have convex sides. We discuss our results in light of several mechanisms that are involved in determining the shape of cells.


Asunto(s)
Fenómenos Fisiológicos Bacterianos , Biofisica/métodos , Escherichia coli/fisiología , Interpretación de Imagen Asistida por Computador/métodos , Modelos Biológicos , Algoritmos , Forma de la Célula , Escherichia coli/metabolismo , Procesamiento de Imagen Asistido por Computador , Luz , Microscopía Fluorescente , Microscopía de Contraste de Fase/métodos , Modelos Estadísticos , Reproducibilidad de los Resultados
7.
Phys Rev E Stat Nonlin Soft Matter Phys ; 71(6 Pt 1): 061920, 2005 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-16089778

RESUMEN

The relaxation of a single DNA molecule is studied. The experimental system consists of optical tweezers and a micron-sized bead that is tethered to the bottom of the sample by a single double-stranded DNA molecule. The bead slows down the DNA relaxation from a strongly stretched configuration such that it is passing through stretched equilibrium states. This allows for a theoretical description of the relaxation trajectory, which is in good agreement with experiment.


Asunto(s)
ADN/química , ADN/ultraestructura , Interpretación de Imagen Asistida por Computador/métodos , Micromanipulación/métodos , Modelos Químicos , Modelos Moleculares , Simulación por Computador , ADN/análisis , Elasticidad , Cinética , Conformación de Ácido Nucleico , Estimulación Física/métodos , Estrés Mecánico
8.
Phys Rev Lett ; 92(9): 098101, 2004 Mar 05.
Artículo en Inglés | MEDLINE | ID: mdl-15089516

RESUMEN

We study the relaxation dynamics of a semiflexible chain by introducing a time-dependent tension. The chain has one of its ends attached to a large bead, and the other end is fixed. We focus on the initial relaxation of the chain that is initially strongly stretched. Using a tension that is self-consistently determined, we obtain the evolution of the end-to-end distance with no free parameters. Our results are in good agreement with single molecule experiments on double stranded DNA.


Asunto(s)
ADN/química , Modelos Químicos , Termodinámica
11.
Talanta ; 55(5): 943-9, 2001 Dec 13.
Artículo en Inglés | MEDLINE | ID: mdl-18968444

RESUMEN

The kinetics of the reaction between double stranded DNA (dsDNA) and formamide is monitored at the single DNA molecule level. We find that stretching of the DNA leads to an accelerated reaction rate and to a shift in the final equilibrium concentrations. The larger the stretching force, the faster the reaction and the larger the denatured fraction of the product DNA. The single molecule kinetics is obtained from the change in the contour length of the DNA which, in turn, is measured using optical tweezers on a microbead-single DNA molecule-cover slip construct.

12.
Biol Cybern ; 83(6): L11-6, 2000 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-11130587

RESUMEN

The stochastic resonance (SR) phenomenon in human cognition (memory retrieval speed for arithmetical multiplication rules) is addressed in a behavioral and neurocomputational study. The results of an experiment in which performance was monitored for various magnitudes of acoustic noise are presented. The average response time was found to be minimal for some optimal noise level. Moreover, it was shown that the optimal noise level and the magnitude of the SR effect depend on the difficulty of the task. A computational framework based on leaky accumulators that integrate noisy information and provide the output upon reaching a threshold criterion is used to illustrate the observed phenomena.


Asunto(s)
Simulación por Computador , Recuerdo Mental/fisiología , Modelos Neurológicos , Tiempo de Reacción/fisiología , Estimulación Acústica , Humanos , Ruido , Procesos Estocásticos
13.
Am J Hum Genet ; 67(1): 197-202, 2000 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-10839976

RESUMEN

Hand-foot-genital syndrome (HFGS) is a rare, dominantly inherited condition affecting the distal limbs and genitourinary tract. A nonsense mutation in the homeobox of HOXA13 has been identified in one affected family, making HFGS the second human syndrome shown to be caused by a HOX gene mutation. We have therefore examined HOXA13 in two new and four previously reported families with features of HFGS. In families 1, 2, and 3, nonsense mutations truncating the encoded protein N-terminal to or within the homeodomain produce typical limb and genitourinary abnormalities; in family 4, an expansion of an N-terminal polyalanine tract produces a similar phenotype; in family 5, a missense mutation, which alters an invariant domain, produces an exceptionally severe limb phenotype; and in family 6, in which limb abnormalities were atypical, no HOXA13 mutation could be detected. Mutations in HOXA13 can therefore cause more-severe limb abnormalities than previously suspected and may act by more than one mechanism.


Asunto(s)
Anomalías Múltiples/genética , Deformidades Congénitas del Pie/genética , Deformidades Congénitas de la Mano/genética , Proteínas de Homeodominio/genética , Mutación/genética , Anomalías Urogenitales/genética , Anomalías Múltiples/diagnóstico por imagen , Niño , Codón sin Sentido/genética , Análisis Mutacional de ADN , Femenino , Deformidades Congénitas del Pie/diagnóstico por imagen , Genes Homeobox/genética , Deformidades Congénitas de la Mano/diagnóstico por imagen , Humanos , Lactante , Masculino , Datos de Secuencia Molecular , Mutación Missense/genética , Linaje , Fenotipo , Radiografía , Eliminación de Secuencia/genética , Síndrome
17.
N Engl J Med ; 341(5): 376-7, 1999 Jul 29.
Artículo en Inglés | MEDLINE | ID: mdl-10428669
18.
19.
Proc Natl Acad Sci U S A ; 96(14): 7916-21, 1999 Jul 06.
Artículo en Inglés | MEDLINE | ID: mdl-10393922

RESUMEN

The polymerization of RecA on individual double-stranded DNA molecules is studied. A linear DNA (lambda DNA, 48.5 Kb), anchored at one end to a cover glass and at the other end to an optically trapped 3-micrometers diameter polystyrene bead, serves as a template. The elongation caused by RecA assembly is measured in the presence of ATP and ATP[gammaS]. By using force extension and hydrodynamic recoil, a value of the persistence length of the RecA-DNA complex is obtained. In the presence of ATP, the polymer length is unstable, first growing to saturation and then decreasing. This suggests a transient dynamics of association and dissociation for RecA on a double-stranded DNA, the process being controlled by ATP hydrolysis. Part of this dynamics is suppressed in the presence of ATP[gammaS], leading to a stabilized RecA-DNA complex. A one-dimensional nucleation and growth model is presented that may account for the protein assembly.


Asunto(s)
Adenosina Trifosfato/metabolismo , ADN/química , ADN/metabolismo , Rec A Recombinasas/química , Rec A Recombinasas/metabolismo , Hidrólisis , Cinética , Poliestirenos , Unión Proteica
20.
Genet Med ; 1(4): 170, 1999.
Artículo en Inglés | MEDLINE | ID: mdl-11258353
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