Publications (8)12.45 Total impact
-
Article: Live cell flattening - traditional and novel approaches.
[show abstract] [hide abstract]
ABSTRACT: Eukaryotic cell flattening is valuable for improving microscopic observations, ranging from bright field (BF) to total internal reflection fluorescence (TIRF) microscopy. Fundamental processes, such as mitosis and in vivo actin polymerization, have been investigated using these techniques. Here, we review the well known agar overlayer protocol and the oil overlay method. In addition, we present more elaborate microfluidics-based techniques that provide us with a greater level of control. We demonstrate these techniques on the social amoebae Dictyostelium discoideum, comparing the advantages and disadvantages of each method.PACS Codes: 87.64.-t, 47.61.-k, 87.80.Ek.PMC Biophysics 01/2010; 3(1):9. -
Article: Contact-mediated cell-assisted cell proliferation in a model eukaryotic single-cell organism: an explanation for the lag phase in shaken cell culture.
[show abstract] [hide abstract]
ABSTRACT: In cell culture, when cells are inoculated into fresh media, there can be a period of slow (or lag phase) growth followed by a transition to exponential growth. This period of slow growth is usually attributed to the cells' adaptation to a new environment. However, we argue that, based on observations of shaken suspension culture of Dictyostelium discoideum, a model single-cell eukaryote, this transition is due to a density effect. Attempts to demonstrate the existence of implicit cell signaling via long-range diffusible messengers (i.e., soluble growth factors) through cell-medium separation and microfluidic flow perturbation experiments produced negative results. This, in turn, led to the development of a signaling model based on direct cell-to-cell contacts. Employing a scaling argument for the collision rate due to fluid shear, we reasonably estimate the crossover density for the transition into the exponential phase and fit the observed growth kinetics.Physical Review E 04/2008; 77(4 Pt 1):041905. · 2.26 Impact Factor -
Article: Dictyostelium discoideum chemotaxis: threshold for directed motion.
[show abstract] [hide abstract]
ABSTRACT: The chemotactic response of Dictyostelium discoideum cells to stationary, linear gradients of cyclic adenosine 3',5'-monophosphate (cAMP) was studied using microfluidic devices. In shallow gradients of less than 10(-3) nM/microm, the cells showed no directional response and exhibited a constant basal motility. In steeper gradients, cells moved up the gradient on average. The chemotactic speed and the motility increased with increasing steepness up to a plateau at around 10(-1) nM/microm. In very steep gradients, above 10 nM/microm, the cells lost directionality and the motility returned to the sub-threshold level. In the regime of optimal response the difference in receptor occupancy at the front and back of the cell is estimated to be only about 100 molecules.European Journal of Cell Biology 10/2006; 85(9-10):981-9. · 2.81 Impact Factor -
Article: Dicyostelium discoideum chemotaxis: Threshold for directed motion
[show abstract] [hide abstract]
ABSTRACT: The chemotactic response of Dictyostelium discoideum cells to stationary, linear gradients of cyclic adenosine 3',5'-monophosphate (cAMP) was studied using microfluidic devices. In shallow gradients of less than 10(-3) nM/mu m, the cells showed no directional response and exhibited a constant basal motility. In steeper gradients, cells moved up the gradient on average. The chemotactic speed and the motility increased with increasing steepness up to a plateau at around 10(-1) nM/mu m. In very steep gradients, above 10 nM/mu m, the cells lost directionality and the motility returned to the sub-threshold level. In the regime of optimal response the difference in receptor occupancy at the front and back of the cell is estimated to be only about 100 molecules. (c) 2006 Elsevier GmbH. All rights reserved.European Journal of Cell Biology 09/2006; 85(9-10):981-989. · 2.81 Impact Factor -
Article: Improving slide-based assays by stirring: application of liquid-on-liquid mixing to immunofluorescence staining of polytene chromosomes.
[show abstract] [hide abstract]
ABSTRACT: A new method for stirring thin liquid films has been developed and demonstrated to increase the sensitivity of immunofluorescence staining of polytene chromosomes. This liquid-on-liquid mixing (LOLM) technique uses a stirrer fluid, immiscible with the thin film, to transmit shear at the liquid-liquid interface. Here, we stir mineral oil layered over an aqueous thin film of antibody solution, which stains transcription apparatuses on chromosomes previously fixed to a glass slide. The quality of staining was assessed at varying antibody concentrations and incubation or stirring times. Our data indicate that the LOLM technique overcomes the diffusion barrier associated with traditional slide-based biological assays.Journal of Biochemical and Biophysical Methods 08/2005; 64(1):59-68. · 2.33 Impact Factor -
Article: Pair correlations of a dilute charged colloidal fluid near a glass wall.
[show abstract] [hide abstract]
ABSTRACT: Using confocal microscopy we examine the static structure of low density, highly charged colloidal suspensions near a repulsive glass boundary. We find no sign of an interparticle attraction of the magnitude noted previously.Physical Review E 05/2003; 67(4 Pt 1):041402. · 2.26 Impact Factor -
Article: Live cell flattening - traditional and novel approaches
[show abstract] [hide abstract]
ABSTRACT: Eukaryotic cell flattening is valuable for improving microscopic observations, ranging from bright field (BF) to total internal reflection fluorescence (TIRF) microscopy. Fundamental processes, such as mitosis and in vivo actin polymerization, have been investigated using these techniques. Here, we review the well known agar overlayer protocol and the oil overlay method. In addition, we present more elaborate microfluidics-based techniques that provide us with a greater level of control. We demonstrate these techniques on the social amoebae Dictyostelium discoideum, comparing the advantages and disadvantages of each method.PMC Biophysics, v.3, 9-1-9-15 (2010). -
Article: Investigation of apparent correlated motion of Brownian particles
[show abstract] [hide abstract]
ABSTRACT: We, as well as other workers, have noticed using light microscopy that particles undergoing Brownian motion can appear to linger around each other for long periods of time. The question arises as to whether this lingering is a product of interparticle interactions, or is an artifact due to random thermal motion and projection onto a two-dimensional image plane. To answer this question, we produced digitized animations of colloidal particles using light microscopy images of a system composed of micrometer-sized latex spheres suspended in water. Six observers, unfamiliar with the experiment, watched these animations for lingering among the particles. Control animations were also generated from these data sets in which correlations due to particle-particle interactions had been destroyed, but the probability of the aforementioned artifactual correlations remained unchanged. We found that the differences in what people observed in the real and control data were not statistically significant. Thus, we conclude that any lingering observed on the time scale of 10 s and the length scale of 5 μm is the result of the random motion of the particles and projection effects. By way of explaining this result theoretically, we find that on this length and time scale, hydrodynamic interactions dominate over electrostatic and van der Waals forces. Accordingly, we present numerical and analytical calculations of the enhanced lingering associated with the decrease in hydrodynamic mobility of closely separated particles. These calculations give results which are consistent with the conclusion that the enhanced lingering effect is too small to be seen by an individual observer.Phys. Rev. E. 56(2).
Top co-authors
Top Journals
Institutions
-
2003–2008
-
Cornell University
- Laboratory of Atomic and Solid State Physics
Ithaca, NY, USA
-
