Correlated 3D light and electron microscopy: Use of high voltage electron microscopy and electron tomography for imaging large biological structures

Both light and electron microscopy have experienced exciting advances in the past few years, driven by the development of new imaging technologies and the ready availability of powerful computers and associated algorithms for visualization, analysis, and image restoration. The concomitant development of molecular genetic methods for engineering fluorescent molecules into proteins and for targeting indicator dyes to subcellular compartments has led to unprecedented opportunities for the study of dynamic processes and for correlating physiology and structure. Although the effective resolution of light microscopy has been increased through the use of optical sectioning and computational deblurring of images, the resolution of the light microscope is still not sufficient to address many issues of cell and tissue structure and protein localization. Electron microscopy has also undergone a quiet revolution, in particular high voltage electron microscopy, where the technique of electron tomography allows 3D reconstruction of relatively large structures such as neuronal spiny dendrites without the need for serial sectioning. In combination with light microscopy, high voltage EM and electron tomography provide a relatively straightforward method to bridge the resolution gap between light and electron microscopy. In this review, we discuss correlated 3D Light and electron microscopy imaging of cells and tissues, including the adaptation of fluorescent dyes for electron microscopy imaging.