Integrated Calendar

Fish and insects live in fluid environments and use numerous techniques to survive in a hostile environment. Small insects beat their wings many times a second, and can couple fluid vortices to the elasticity of their wings to generate optimal flight modes within short time scales. Motivated by such observations, we borrowed such passive techniques to design a small swimming robot, equipped with a flexible tail. The robot is capable of swimming at high speeds, but more importantly its thrust is maximized at a frequency where the elasticity of the tail couples strongly with the fluid environment, beyond just added mass effects. In this talk we will discuss the physical principles that govern the kinematics of this robotic device.

Live-cell imaging allows the investigation of dynamic processes inside living cells, where macromolecular crowding is proposed to influence various properties of proteins. We have previously demonstrated how Förster Resonance Energy Transfer (FRET) can be used to determine binding dynamics between proteins in living cells. Here we follow catalysis within HeLa cells in real time, to determine ezymatic reaction parameters (Km, kcat) from single cell measurements and to relate them to their values in vitro under different conditions. Measurement protocols were developed for two enzymes, fluorescently labeled TEM1 β-lactamase and β-galactosidase degrading fluorogenic substrates. The enzymatic reactions were initiated by microinjection of the substrate and monitored by FRET and/or detecting the intensity change of the cleaved molecule. Our experimental setup enables us to determine enzymatic constants inside the cell. This allows determining cell-to-cell variability in catalytic efficiency. Moreover, we used mutations that affect Km and kcat to see how in vitro changes are manifested in live cells. In addition to the in vivo work, we investigate the enzymatic reaction in vitro and in HeLa cell extracts. For data analysis of the single progress curves three models were compared, (i) analytic approximation of the Lambert function, (ii) the Lambert W-function including an exponential fit and (iii) computer simulation. Our results show that there is a big difference in the catalytic efficiency in vitro compared to in vivo data, what explanation needs further studies (cellular crowding, pH, in-cell redox conditions, etc.).

In the mammalian retina, visual information is transduced into electrical signals by photoreceptors. These signals are transmitted from photoreceptors to bipolar cells and on to ganglion cells, which inform the brain about contrast, form, color, object motion and other features of the visual world. On its route through the retina, visual information is modulated by inhibitory networks formed by horizontal and amacrine cells. Here, I focus on horizontal cells. At so-called triad synapses, these interneurons receive glutamatergic input from photoreceptors and provide feedback and feedforward signals to photoreceptors and bipolar cells, respectively. In recent years, we used different techniques to analyze the role of horizontal cells: we 1) deleted electrical synapses between horizontal cells, 2) ablated the entire horizontal cell population, and 3) selectively silenced horizontal cells by input deprivation. From these studies we gathered that horizontal cells are important for the spatial and temporal tuning of ganglion cells and are necessary to maintain the integrity of the first synapse in the visual system.