Cellular labels are essential components in the toolbox to build our current understanding of biological function. Yet, a versatile, efficient and non-invasive approach to tag individual cells chosen upon observation is still lacking.

The vast majority of methods for generating fluorescently labelled cells rely on biochemical characteristics that are common to an ensemble of cells in a sample, and lack the specificity given by imaging. Widely used methods include transfection of genes encoding fluorescent proteins, membrane-permeable dyes or antibody labelling. These approaches do not allow targeting specific cells among a large population of the same type. Furthermore, their efficiency and specificity are highly dependent on stochastic events and molecular affinity properties, often yielding a sub-optimal fraction of correctly labelled cells.

Spatially targeted methods, such as single-cell electroporation, microinjection^, laser capture microdissection or transfection of photo-switchable proteins that change properties upon illumination are often invasive, labor-intensive or lack accuracy, rendering them impractical for a wide range of applications.

Researchers introduce a novel laser-based technique, cell labelling via photobleaching (CLaP), for labelling individual cells in culture. Specific cells can be chosen based on their morphological characteristics, dynamic behavior, localization in the sample at a given time, or any visible feature that distinguishes the cells of interest from an ensemble.

CLaP allows combining the accuracy and versatility of image-based selection with the high throughput of automated cell-sorting methods, thus permitting experiments that account for cellular context or temporal dynamics, such as transcriptomic profiling preserving spatial information.

The method does not require previous knowledge of cell surface markers, uses off-the-shelf reagents, and may be implemented on a standard confocal microscope without hardware or software modification.

http://www.nature.com/ncomms/2016/160520/ncomms11636/full/ncomms11636.html