The expression of green fluorescent protein in heterologous systems in 1994 spawned for light microscopy what has been called the “green revolution,” allowing researchers to visualize individual protein molecules in cells.
In a recent paper, Shu et al first review attempts to produce similar molecules for electron microscopy, such as horseradish peroxidase, but conclude that they all have serious drawbacks. They then report their engineering of a protein molecule called miniSOG, a fluorescent molecule that is also an efficient oxygen generator. The only cofactor of this protein is flavin mononucleotide, which is necessary for the mitochondrial electron transport chain and is thus present in nearly all cells.
In cultured HeLa cells, they fused miniSOG to cytochrome C to show that expressing this molecule is able to mark mitochondria in both light and electron microscopy:
The researchers also fused miniSOG to an isoform of SynCAM, a cell adhesion protein that is expected to localize post-synaptically. They then used serial block face scanning em in mouse tissues to determine the location of their marker in 3d space. They show this 3d reconstruction from 2d image stacks in a 1.5 min supplementary video, which I’ve uploaded here and am embedding for your viewing pleasure:
The only problem I can see is that the “miniSOG revolution” isn’t nearly as catchy a name as the “green revolution.” Any suggestions?
Shu X, Lev-Ram V, Deerinck TJ, Qi Y, Ramko EB, et al. (2011) A Genetically Encoded Tag for Correlated Light and Electron Microscopy of Intact Cells, Tissues, and Organisms. PLoS Biol 9(4): e1001041. doi:10.1371/journal.pbio.1001041