Thumbnail image of

Patricia Le Baccon is Facility Manager for Light Microscopy, UMR 218 and PICT-IBiSA, at the Institut Curie, Paris, France

These days the use of a photonic microscope in biology is routine. The vast majority of cell biology articles published today have at least one figure containing a microscopy image. Microscopes have, for quite some time, been used as more than mere tools for perceiving the relative locations of biological structures; they are now applied for the analysis of dynamics, interactions, subtle structural details, and a variety of other static and dynamic measurements. The increasing use of fluorescence microscopy goes hand in hand with revolutions in molecular biology over the past 20 years. The advent of green fluorescent protein (GFP) in parallel with progress in detector technology, optics, and electronics, was a first step toward dynamic and live imaging. GFP opened the door to live cell imaging and at the same time allowed dynamic studies to be performed in vivo. Recently, the breaking of the diffraction limit by high-resolution microscopy has ushered in new ways of perceiving cells and understanding cellular mechanisms in fine detail.

The launch of such technologies as commercially available systems allows numerous laboratories to exploit the new tools to answer biological questions. Nevertheless, it is necessary to be well-informed about the strengths and limitations of each method, and to apply a degree of caution when interpreting the data generated. Here we present a series of articles reviewing the state of the art in these tools, which allow cells to be studied right down to the molecular level.

The optimization of probes to monitor the dynamic of structures and molecules in vivo is one aspect of recent progress. This optimization of fluorophores increases the signal to noise ratio and, as a consequence, the spatial and temporal resolution of the systems. Articles by R. Day and M. Davidson and P. Pantazis et al. review applications of FRET and a new type of probe (nanoprobes for SHG) for exciting new applications. With such probes we are able to investigate, in vivo, molecular interactions, the nature of which poses very fundamental questions for labs around the world. Various techniques have been developed to identify and analyze molecular interactions using microscopes, such as FRET, FCS, and RICS. Articles by M. Digman and E. Gratton, S. Padilla-Parra and M. Tramier, and J. Ries and P. Schwille take us on a tour of these techniques, assessing their limitations and discussing means to circumvent such inconveniences. Similar problems apply to high resolution microscopy and the breaking of the diffraction barrier. In this special issue, articles by S. Saka and S. Rizzoli, P. Sengupta and J. Lippincott-Schwartz, J. Huiksen, and Y. Markaki et al. bring to our attention the technical limits, future solutions, and the caution that we need to apply to data interpretation. “Jump over” the limit of diffraction is the result of progress in engineering over the last ten years or so, and as biologists we need to catch up in order to reap the benefits fully. That is the purpose of the article by S. van Teeffelen et al.: extracting the qualitative and quantitative information from images is a challenge, especially with live cell imaging. This topic is an important area for future developments in imaging techniques.

The future directions of light microscopy are various, and many new doors are opening with, for example correlation microscopy (e.g. synthesizing new insights by combining electron microscopy with light microscopy data), high-throughput technologies, and intra-vital imaging. Some of the “futuristic” prospects are detailed by J. Swedlow as an introduction to this special issue of BioEssays. We wish you enjoyable and informative reading!

Patricia Le Baccon

Guest Editor

Andrew Moore