Showing papers by "Helge Ewers published in 2008"

Human papillomavirus type 16 entry: retrograde cell surface transport along actin-rich protrusions.

Abstract: The lateral mobility of individual, incoming human papillomavirus type 16 pseudoviruses (PsV) bound to live HeLa cells was studied by single particle tracking using fluorescence video microscopy. The trajectories were computationally analyzed in terms of diffusion rate and mode of motion as described by the moment scaling spectrum. Four distinct modes of mobility were seen: confined movement in small zones (30–60 nm in diameter), confined movement with a slow drift, fast random motion with transient confinement, and linear, directed movement for long distances. The directed movement was most prominent on actin-rich cell protrusions such as filopodia or retraction fibres, where the rate was similar to that measured for actin retrograde flow. It was, moreover, sensitive to perturbants of actin retrograde flow such as cytochalasin D, jasplakinolide, and blebbistatin. We found that transport along actin protrusions significantly enhanced HPV-16 infection in sparse tissue culture, cells suggesting a role for in vivo infection of basal keratinocytes during wound healing.

Even illumination in total internal reflection fluorescence microscopy using laser light.

Abstract: In modern fluorescence microscopy, lasers are a widely used source of light, both for imaging in total internal reflection and epi-illumination modes. In wide-field imaging, scattering of highly coherent laser light due to imperfections in the light path typically leads to nonuniform illumination of the specimen, compromising image analysis. We report the design and construction of an objective-launch total internal reflection fluorescence microscopy system with excellent evenness of specimen illumination achieved by azimuthal rotation of the incoming illuminating laser beam. The system allows quick and precise changes of the incidence angle of the laser beam and thus can also be used in an epifluorescence mode.

Probing the dynamics of protein-protein interactions at neuronal contacts by optical imaging.

Abstract: 8.1. Principle and Methodological Requirements 1580 8.2. The Autocorrelation Function 1581 8.3. The Photon-Counting Histogram 1582 8.4. Fluorescence Cross-Correlation Spectroscopy 1582 9. Direct Assessment of Protein/Protein Interactions by FRET 1583 9.1. Definition and Basic Properties 1583 9.2. Fluorescence Lifetime Imaging (FLIM) 1584 10. Conclusion 1585 11. Acknowledgments 1585 12. References 1585