Cyclic GMP (cGMP) is a ubiquitous second messenger in eukaryotic cells. It is assumed to regulate the association of myosin II with the cytoskeleton of motile cells. When cells of the social amoeba Dictyostelium discoideum are exposed to chemoattractants or to increased osmotic stress, intracellular cGMP levels rise, preceding the accumulation of myosin II in the cell cortex. To directly investigate the impact of intracellular cGMP on cytoskeletal dynamics in a living cell, we released cGMP inside the cell by laser-induced photo-cleavage of a caged precursor. With this approach, we could directly show in a live cell experiment that an increase in intracellular cGMP indeed induces myosin II to accumulate in the cortex. Unexpectedly, we observed for the first time that also the amount of filamentous actin in the cell cortex increases upon a rise in the cGMP concentration, independently of cAMP receptor activation and signaling. We discuss our results in the light of recent work on the cGMP signaling pathway and suggest possible links between cGMP signaling and the actin system. Insight, innovation, integrationSecond messengers like cGMP play a central role in the regulatory pathways of living cells. Here, we demonstrate that an increase in intracellular cGMP can trigger not only myosin II but also actin responses in motile amoeboid cells. In previous studies, an increase in intracellular cGMP was induced indirectly via membrane receptor stimulation. In the present work, we employ, for the first time, the direct light-induced release of cGMP from a caged precursor to raise the cytosolic cGMP level in Dictyostelium cells that carry fluorescent markers for filamentous actin and myosin II. Based on this advanced combination of live cell photo-uncaging and multi-color confocal microscopy, we could identify a link between cGMP and actin dynamics in motile amoeboid cells.

In this work, the fabrication and characterization of a simple, inexpensive, and effective microfluidic paper analytic device (µPAD) for monitoring DNA samples is reported. The glass microfiber-based chip has been fabricated by a new wax-based transfer-printing technique and an electrode printing process. It is capable of moving DNA effectively in a time-dependent fashion. The nucleic acid sample is not damaged by this process and is accumulated in front of the anode, but not directly on the electrode. Thus, further DNA processing is feasible. The system allows the DNA to be purified by separating it from other components in sample mixtures such as proteins. Furthermore, it is demonstrated that DNA can be moved through several layers of the glass fiber material. This proof of concept will provide the basis for the development of rapid test systems, e.g., for the detection of pathogens in water samples.

Chemotactic motion in a chemical gradient is an essential cellular function that controls many processes in the living world. For a better understanding and more detailed modelling of the underlying mechanisms of chemotaxis, quantitative investigations in controlled environments are needed. We developed a setup that allows us to separately address the dependencies of the chemotactic motion on the average background concentration and on the gradient steepness of the chemoattractant. In particular, both the background concentration and the gradient steepness can be kept constant at the position of the cell while it moves along in the gradient direction. This is achieved by generating a well-defined chemoattractant gradient using flow photolysis. In this approach, the chemoattractant is released by a light-induced reaction from a caged precursor in a microfluidic flow chamber upstream of the cell. The flow photolysis approach is combined with an automated real-time cell tracker that determines changes in the cell position and triggers movement of the microscope stage such that the cell motion is compensated and the cell remains at the same position in the gradient profile. The gradient profile can be either determined experimentally using a caged fluorescent dye or may be alternatively determined by numerical solutions of the corresponding physical model. To demonstrate the function of this adaptive microfluidic gradient generator, we compare the chemotactic motion of Dictyostelium discoideum cells in a static gradient and in a gradient that adapts to the position of the moving cell.

Many cellular processes involve the translocation of proteins from the cytosolic region to the cortex of the cell and vice versa. The dynamics of such processes is typically investigated by fluorescence imaging of GFP-labeled versions of these proteins. Quantitative analysis of the resulting fluorescence images requires image segmentation procedures that identify the cell within the image and subsequently divide the cell into a cytosolic and a cortical region to monitor the temporal evolution of the fluorescence signals within these parts of the cell separately. Here, we present an image segmentation protocol that we have developed for this type of data analysis. It consists of noise reduction, normalization, and thresholding steps to generate masks that define the cytosolic and the cortical regions of a cell. Based on these masks, the desired fluorescence signals can be extracted from the confocal microscopy images.