ReAsH: another viable option for in vivo protein labelling in Dictyostelium

Imaging flow cytometry analysis of intracellular pathogens

Imaging flow cytometry has been applied to address questions in infection biology, in particular, infections induced by intracellular pathogens. This methodology, which utilizes specialized analytic software makes it possible to analyze hundreds of quantified features for hundreds of thousands of individual cellular or subcellular events in a single experiment. Imaging flow cytometry analysis of host cell-pathogen interaction can thus quantitatively addresses a variety of biological questions related to intracellular infection, including cell counting, internalization score, and subcellular patterns of co-localization. Here, we provide an overview of recent achievements in the use of fluorescently labeled prokaryotic or eukaryotic pathogens in human cellular infections in analysis of host-pathogen interactions. Specifically, we give examples of Imagestream-based analysis of cell lines infected with Toxoplasma gondii or Mycobacterium tuberculosis. Furthermore, we illustrate the capabilities of imaging flow cytometry using a combination of standard IDEAS™ software and the more recently developed Feature Finder algorithm, which is capable of identifying statistically significant differences between researcher-defined image galleries. We argue that the combination of imaging flow cytometry with these software platforms provides a powerful new approach to understanding host control of intracellular pathogens.

Exploration of biarsenical chemistry--challenges in protein research

The fluorescent modification of proteins (with genetically encoded low-molecular-mass fluorophores, affinity probes, or other chemically active species) is extraordinarily useful for monitoring and controlling protein functions in vitro, as well as in cell cultures and tissues. The large sizes of some fluorescent tags, such as fluorescent proteins, often perturb normal activity and localization of the protein of interest, as well as other effects. Of the many fluorescent-labeling strategies applied to in vitro and in vivo studies, one is very promising. This requires a very short (6- to 12-residue), appropriately spaced, tetracysteine sequence (-CCXXCC-); this is either placed at a protein terminus, within flexible loops, or incorporated into secondary structure elements. Proteins that contain the tetracysteine motif become highly fluorescent upon labeling with a nonluminescent biarsenical probe, and form very stable covalent complexes. We focus on the development, growth, and multiple applications of this protein research methodology, both in vitro and in vivo. Its application is not limited to intact-cell protein visualization; it has tremendous potential in other protein research disciplines, such as protein purification and activity control, electron microscopy imaging of cells or tissue, protein-protein interaction studies, protein stability, and aggregation studies.

Rapid FlAsH labelling in the budding yeast Saccharomyces cerevisiae

Live cell imaging of protein distributions is an essential tool in modern cell biology. It relies on the functional labelling of a host protein with a fluorophore, which may either be a genetically fused fluorescent protein or an organic dye binding to the host protein. The biarsenical-tetracysteine system or 'FlAsH-labelling', is based on the high affinity interaction between a biarsenical probe and a small protein tag. This approach has been successfully used for live cell imaging in the budding yeast Saccharomyces cerevisiae. However, the established labelling protocols require a lengthy overnight incubation of the cells with the dye under tightly controlled growth conditions, which severely limits the use of this approach. In this study, we characterize an efficient method for introducing FlAsH-EDT(2) into live budding yeast cells using standard electroporation. The labelling time is reduced from more than 12 h to less than 1 h without compromising the labelling efficiency or cell viability. This approach may be used for cells in different growth phases or grown under different conditions. It may be further extended to other small high affinity probes, thus opening up new possibilities for labelling in budding yeast.

Multi-dimensional correlative imaging of subcellular events: combining the strengths of light and electron microscopy

To genuinely understand how complex biological structures function, we must integrate knowledge of their dynamic behavior and of their molecular machinery. The combined use of light or laser microscopy and electron microscopy has become increasingly important to our understanding of the structure and function of cells and tissues at the molecular level. Such a combination of two or more different microscopy techniques, preferably with different spatial- and temporal-resolution limits, is often referred to as 'correlative microscopy'. Correlative imaging allows researchers to gain additional novel structure-function information, and such information provides a greater degree of confidence about the structures of interest because observations from one method can be compared to those from the other method(s). This is the strength of correlative (or 'combined') microscopy, especially when it is combined with combinatorial or non-combinatorial labeling approaches. In this topical review, we provide a brief historical perspective of correlative microscopy and an in-depth overview of correlative sample-preparation and imaging methods presently available, including future perspectives on the trend towards integrative microscopy and microanalysis.