A stable chemokine gradient controls directional persistence of migrating dendritic cells

Navigation of dendritic cells (DCs) from the site of infection to lymphoid organs is guided by concentration gradients of CCR7 ligands. How cells interpret chemokine gradients and how they couple directional sensing to polarization and persistent chemotaxis has remained largely elusive. Previous experimental systems were limited in the ability to control fast de novo formation of the final gradient slope, long-lasting stability of the gradient and to expose cells to dynamic stimulation. Here, we used a combination of microfluidics and quantitative in vitro live cell imaging to elucidate the chemotactic sensing strategy of DCs. The microfluidic approach allows us to generate soluble gradients with high spatio-temporal precision and to analyze actin dynamics, cell polarization, and persistent directional migration in both static and dynamic environments. We demonstrate that directional persistence of DC migration requires steady-state characteristics of the soluble gradient instead of temporally rising CCL19 concentration, implying that spatial sensing mechanisms control chemotaxis of DCs. Kymograph analysis of actin dynamics revealed that the presence of the CCL19 gradient is essential to stabilize leading edge protrusions in DCs and to determine directionality, since both cytoskeletal polarization and persistent chemotaxis are abrogated in the range of seconds when steady-state gradients are perturbed. In contrast to Dictyostelium amoeba, DCs are unable to decode oscillatory stimulation of soluble chemokine traveling waves into a directional response toward the wave source. These findings are consistent with the notion that DCs do not employ adaptive temporal sensing strategies that discriminate temporally increasing and decreasing chemoattractant concentrations in our setting. Taken together, in our experimental system DCs do not depend on increasing absolute chemokine concentration over time to induce persistent migration and do not integrate oscillatory stimulation. The observed capability of DCs to migrate with high directional persistence in stable gradients but not when subjected to periodic temporal cues, identifies spatial sensing as a key requirement for persistent chemotaxis of DCs

Untersuchung zur Wirkung ultravioletter Strahlung im Bereich zwischen 289 nm und 334 nm auf eukariontische Zellen Schlussbericht

In a study on the effect of monochromatic and polychromatic UV light on eukaryontic cells the following action spectra were determined: (I) Action spectras for the inactivation and mutation induction for the ouabain resistance in Chinese hamster cells between 254 nm and 313 nm, as well as under simulated sunlight, (II) action spectra for the induction of sister chromatid exchanges in Chinese hamster cells, (III) action spectra for the inactivation and mutation induction for cavanine resistance in yeast between 254 nm and 334 nm, as well as under simulated sunlight. Action spectra III closely resemble the absorption spectra of DNA, which is regarded as the primary chromophore. Discrepancies between calculated and measured actions of simulated sunlight point to an effective repair mechanism in yeast cells. Spectra II and I are interpreted by assuming another chromophore. In addition, in the case II an absorption by proteins is discussed. The effect of natural sunlight can be described as an additive action by light of the different wavelengths. An interaction with UV light cannot be excluded. (WEN)Available from TIB Hannover: F94B1847+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman

Zellulaere Wirkungen mono- und polychromatischer UVB-Strahlung Untersuchungen an Hefe- und Saeugerzellen

Available from TIB Hannover: RO 9717(1990,4) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Computational models for musical sounds sources

As a result of the progress in information technologies, algorithms for sound generation and transformation are now ubiquitous in multimedia systems, even though their performance and quality is rarely satisfactory. For the specific needs of music production and multimedia art, sound models are needed which are versatile, responsive to user's expectations, and having high audio quality. Moreover, for human-machine interaction model flexibility is a major issue. We will review some of the most important computational models that axe being used in musical sound production, and we will see that models based on the physics of actual or virtual objects can meet most of the requirements, thus allowing the user to rely on high-level descriptions of the sounding entities