Biology subjects

Sandmeyer, A.

Publications and source records attributed to Sandmeyer, A..

4 recordsLinked to original sources

bioRxiv2020

Recruitment of Env to the HIV-1 T cell virological synapse by targeted and sustained Env recycling

HIV-1 infection is enhanced by cell-cell adhesions between infected and uninfected T cells called virological synapses (VS). VS are initiated by the interactions of cell-surface HIV-1 envelope glycoprotein (Env) and CD4 on target cells and act as sites of viral assembly and viral transfer between cells. To study the process that recruits and retains HIV-1 Env at the VS, a replication-competent HIV-1 clone carrying an Env-sfGFP fusion protein was designed to enable live tracking of Env within infected cells. Using surface pulse-labeling of Env and fluorescence recovery after photobleaching (FRAP) studies, we observed targeted accumulation and sustained recycling of Env between the endocytic recycling compartment (ERC) and the VS. We observed dynamic exchange of Env at the VS while the viral structural protein, Gag, was largely immobile at the VS. The disparate exchange rates of Gag and Env at the synapse indicate that retention of Env is not likely to be maintained by entrapment into an immobile Gag lattice or through immobilizing interactions with CD4 on the target cell. A FRAP study of an Env endocytosis mutant showed that recycling is required for the rapid exchange of Env at the VS. We conclude that the mechanism of Env accumulation at the VS and incorporation into nascent particles involves continuous internalization and targeted secretion rather than irreversible interactions with the budding virus.

microbiology↗

bioRxiv2020

Simulating digital micromirror devices for patterning coherent excitation light in structured illumination microscopy

Digital micromirror devices (DMDs) are spatial light modulators that employ the electro-mechanical movement of miniaturized mirrors to steer and thus modulate the light reflected of a mirror array. Their wide availability, low cost and high speed make them a popular choice both in consumer electronics such as video projectors, and scientific applications such as microscopy. High-end fluorescence microscopy systems typically employ laser light sources, which by their nature provide coherent excitation light. In super-resolution microscopy applications that use light modulation, most notably structured illumination microscopy (SIM), the coherent nature of the excitation light becomes a requirement to achieve optimal interference pattern contrast. The universal combination of DMDs and coherent light sources, especially when working with multiple different wavelengths, is unfortunately not straight forward. The substructure of the tilted micromirror array gives rise to a blazed grating, which has to be understood and which must be taken into account when designing a DMD-based illumination system. Here, we present a set of simulation frameworks that explore the use of DMDs in conjunction with coherent light sources, motivated by their application in SIM, but which are generalizable to other light patterning applications. This framework provides all the tools to explore and compute DMD-based diffraction effects and to simulate possible system alignment configurations computationally, which simplifies the system design process and provides guidance for setting up DMD-based microscopes.

biophysics↗

bioRxiv2019

DMD-based super-resolution structured illumination microscopy visualizes live cell dynamics at high speed and low cost

Structured illumination microscopy (SIM) is among the most widely used super-resolution fluorescence microscopy techniques for visualizing the dynamics of cellular organelles, such as mitochondria, the endoplasmic reticulum, or the cytoskeleton. In its most wide-spread implementation, SIM relies on the creation of an interference pattern at the diffraction limit using the coherent addition of laser beams created by a diffraction pattern.\n\nSpatial light modulators based on liquid crystal displays allow SIM micro-scopes to run at image rates of up to hundreds of super-resolved images per second. Digital micromirror devices are another natural choice for creating interference-based SIM patterns, but are not used to their fullest potential because of the blazed grating effect. This effect arises due to the fixed angles between which the mirrors can be switched, creating a sawtooth arrangement of mirrors and thus leading to a change in the intensity distribution of the diffracted beams. This results in SIM patterns with varying modulation contrast which are prone to reconstruction artifacts.\n\nWe have carefully studied the blazed grating effect of DMDs by simulations, varying a range of parameters and compared the simulation results with experiments. This allowed us to identify settings which result in very high modulation contrast across all angles and phases required to generate 2-beam SIM pattern. The use of inexpensive industry-grade CMOS cameras as well as low-cost lasers enabled us to construct a cost-effective, high-speed SIM system. Reconstruction of the super-resolved SIM images is achieved on a recently demonstrated parallel-computing platform, which allowed us to visualize living cells with super-resolution at multiple reconstructed frames per second in real time. We demonstrate the versatility of this new platform by imaging cellular organelle dynamics based on live-cell fluorescent stains as well as with fluorescent protein stained samples.

biophysics↗

bioRxiv2018

A cost-effective approach to Super-resolution Optical Fluctuation (SOFI) microscopy using an industry-grade CMOS camera

Super-resolution (SR) fluorescence microscopy, especially at high speeds, is typically carried out on high-performance research microscopes. The substantial cost of such equipment, combined with the limited distribution of such instruments in imaging facilities, have complicated access to super-resolution imaging for research groups in the biosciences. In this work we promote the accessibility of Super-resolution Optical Fluctuation Imaging (SOFI) to the scientific community by demonstrating its flexibility in terms of the minimal required performance of the imaging system. We show that SOFI data can be acquired using a very cost-efficient industrial-grade detector on both a standard research microscope and an entirely home-built wide-field system. This enables more scientists to enter the field of live-cell super-resolution imaging, as it provides access to a robust and fast SR imaging modality at comparatively modest cost.

biophysics↗