Aspergillus nidulans swoQ Plays an Important Role in Polarized Hyphal Growth

Filamentous fungi form polarized hyphae by concentrating the addition of new material at the apex of the cell. The mechanics of polarized hyphal growth are coordinated by the cytoskeleton which utilizes microtubules (MTs) and filamentous actin in order to facilitate vesicle trafficking. The cytoskeletal machinery implicated in the regulation of endocytosis and exocytosis during polarized growth is complex and has been studied extensively in recent years. Despite these efforts there are many gaps in the current growth model, and the exact role of the cytoskeleton on secretion and internalization mechanisms during polarized growth remains to be elucidated. In order to address this knowledge gap, this study investigates the contribution of cytoskeletal elements on polarized growth. In this study, I identified the Aspergillus nidulans temperature-sensitive (TS) mutant, swoQ. A mutant allele in the swoQ gene results in abnormal polarity maintenance and cell morphogenesis in the swoQ strain, as evidenced by the presence of abnormally swollen cells. A forward genetic screen revealed the swoQ polarity defect was suppressed following transformation with the pRG3-47-1 library plasmid which encodes myoA, a class I myosin motor protein. A sub-clone of myoA was introduced into the swoQ mutant and wild-type which resulted in restoration of polarized growth in the polarity mutant and hyper-branching in both strains. To further assess the influence of swoQ, the localization of various polarity markers including: FimA::GFP, Exo84::GFP, DnfA::GFP, and DnfB::GFP, were examined in the mutant strain. The localization of FimA::GFP and Exo84::GFP was abnormal in the swoQ mutant. FimA is an actin nucleating protein which works alongside MyoA, an essential myosin in A. nidulans. Together these proteins facilitate the formation of actin patches which drive endocytosis. Here I show that overexpression of MyoA has a polarization effect on growing cells and is able to suppress the growth defect of the swoQ mutant

On-Chip Detection of Beads with a New Electrical Impedance Sensor

Electrical impedance measurements in microfluidic chips are used for single cell analysis. Parallel electrodes are more suited than planar ones since the electrical field distribution is more homogenous. Previous studies showed methods to make parallel electrodes by incorporating an additional layer between two glass wafers, making electrical connections to both sides needed. Also alignment of electrodes is necessary, making the fabrication of parallel electrodes more elaborate. Therefore a new, simpler fabrication method is developed for the fabrication of parallel electrode chips by incorporating a floating electrode in the microchannel just by adding one step in the fabrication process. In this way, only one side of the chip contains electrical connections. Finally, electrical impedance measurements with 3 and 6 µm polystyrene beads were done. All beads were detected and we have shown that it is possible to distinguish the two beads sizes from each other with a confidence level of 95%, based on the relative change in the electrical impedance

A new probe for measuring electrolytic conductance

A conductance cell of which the electrodes are provided with a 110 nm thick Ta2O5 insulating film is proposed and realized. The stable and very low impedance of the total oxide/solution interface largely reduces interference from redox processes. Measurement results, given as an output voltage between 10 and 600 mV as a function of the specific resistance between 0.1 and 8 k¿, are shown to be in agreement with theoretically calculated results, both at the constant current and constant voltage mode of operation

Dynamic behaviour of ISFET-based sensor-actuator systems

Rapid acid-base titrations can be performed at the surface of a noble-metal electrode with coulometrically generated ions. An ISFET is used as an indicator electrode to detect the equivalence point in the resulting titration curve. The time needed to reach the equivalence point is typically 0.5 to 10 s for acid/base concentrations ranging from 0.5 × 10−3 to 20 × 10−3 mol l−1.\ud \ud A model is presented describing the concentration profiles which appear during the coulometric generation of ions. The result of this model is in good agreement with corresponding measurements. These measurements are carried out with two different actuator electrodes, of which the processing steps are described

High-throughput on-chip DNA fragmentation

free microfluidic deoxyribonucleic acid (DNA) fragmentation chip that is based on hydrodynamic shearing. Genomic DNA has been reproducibly fragmented with 2-10 kbp fragment lengths by applying hydraulic pressure ΔP across micromachined constrictions in the microfluidic channels. The utilization of a series of constrictions reduces the variance of the fragmented DNA length distribution; and parallel microfluidic channels design eliminates the device clogging

A micro CO2 gas sensor based on sensing of pH-sensitive hydrogel swelling by means of a pressure sensor

In this paper a sensor is presented for the detection of carbon dioxide gas inside the stomach in order to diagnose gastrointestinal ischemia. The operational principle of the sensor is measuring the CO/sub 2/ induced pressure generation of a confined pH-sensitive hydrogel by means of a micro pressure sensor. The sensor is capable of measuring CO/sub 2/ with a response time between 2 and 4 minutes and a maximum pressure of 0.29/spl times/10/sup 5/ Pa at 20 kPa CO/sub 2/. The sensor is able to resist up to 1 M HCl acid as can be present inside the stomach. The results are very promising for real application and clinical trials are planned

Chemically modified field effect transistors: the effect of ion-pair association on the membrane potentials

A theoretical model has been developed which relates physically accessible parameters to the formation of a membrane potential. The description is an extension of a theoretical description presented previously by our group, now including divalent cations and ion-pair association. Simulations of the overall membrane potential reveal several factors that may lead to non-Nernstian response curves. For monovalent and divalent cations a reduction in the slope of the response curve (sub-Nernstian response) should virtually always be expected when ion-pair association takes place in the membrane. Ion-pair association of divalent cations and sample anions can lead to a super-Nernstian response. A diffusion potential generally reduces the Nernstian slope of the response curve. In addition, several experimental results are described which illustrate and confirm our theoretical model