Biology subjects

Hummert, J.

Publications and source records attributed to Hummert, J..

3 recordsLinked to original sources

bioRxiv2024

Fast volumetric fluorescence lifetime imaging of multicellular systems using single-objective light-sheet microscopy

Fluorescence lifetime imaging (FLIM) is widely used for functional and multiplexed bioimaging. The lifetime of autofluorescence or fluorescent sensors encodes physiologically relevant parameters. Thus, FLIM is especially relevant for the investigation of living systems. However, application of FLIM to live specimen is hampered by its slow speed and high phototoxicity. To enable faster and gentler FLIM, we integrated single-objective light-sheet microscopy with pulsed excitation and time-resolved detection on a novel SPAD array detector. We achieved 10-100-fold acceleration compared to confocal FLIM, down to 100 ms acquisition time per image, with excellent quantitative agreement. The massively enhanced speed enables volumetric FLIM acquisitions on live multicellular specimens, which we demonstrate with lifetime-based multiplexing in 3D and time-lapse FLIM of tension probes on living embryonic organoids. We benchmark both scanned and static light-sheet modalities to facilitate adding FLIM capability to a large variety of light-sheet microscopes.

biophysics↗

bioRxiv2023

A General Method to Accurately Count Molecular Complexes and Determine the Degree of Labelling in Cells Using Protein Tags

Determining the label to target ratio, also known as degree of labelling (DOL), is crucial for quantitative fluorescence microscopy and a high DOL with minimal unspecific labelling is beneficial for fluorescence microscopy in general. Yet, robust, versatile, and easy-to-use tools for measuring cell-specific labelling efficiencies are not available. This study presents a novel DOL determination technique named Protein-tag DOL (ProDOL), which enables fast DOL measurements and optimisation of protein-tag labelling. With ProDOL various factors affecting labelling efficiency, including substrate type, incubation time, and concentration, as well as sample fixation and cell type can be easily assessed. We applied ProDOL to investigate how HIV-1 pathogenesis factor Nef modulates CD4 T cell activation measuring total and activated copy numbers of the adaptor protein SLP-76 in signalling microclusters. ProDOL proved to be a versatile and robust tool for labelling calibration, enabling determination of labelling efficiencies, optimisation of strategies, and quantification of protein stoichiometry.

cell biology↗

bioRxiv2020

Photobleaching step analysis for robust determination of protein complex stoichiometries

The composition of cellular structures on the nanoscale is a key determinant of macroscopic functions in cell biology and beyond. Different fluorescence single-molecule techniques have proven ideally suited for measuring protein copy numbers of cellular structures in intact biological samples. Of these, photobleaching step analysis poses minimal demands on the microscope and its counting range has significantly improved with more sophisticated algorithms for step detection, albeit at an increasing computational cost. Here, we present a comprehensive framework for photobleaching step analysis, optimizing both data acquisition and analysis. To make full use of the potential of photobleaching step analysis, we evaluate various labelling strategies with respect to their molecular brightness and photostability. The developed analysis algorithm focuses on automation and computational efficiency. Moreover, we benchmark the framework with experimental data acquired on DNA origami labeled with defined fluorophore numbers to demonstrate counting of up to 35 fluorophores. Finally, we show the power of the combination of optimized trace acquisition and automated data analysis for robust protein counting by counting labelled nucleoporin 107 in nuclear pore complexes of intact U2OS cells. The successful in situ application promotes this framework as a new resource enabling cell biologists to robustly determine the stoichiometries of molecular assemblies at the single-molecule level in an automated fashion.

biophysics↗