Scientists are hoping to rejuvenate electron microscopy by creating a new type of genetic tag visible under an electron microscope that can illuminate life in never-before-seen detail.
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CAMBRIDGE: Scientists in the U.S. have illuminated life in previously unseen detail, creating a genetic tag that allows sub-cellular structures to be labelled at nanometre resolutions. It’s hoped that this research will rejuvenate electron microscopy.
In the study, a plant protein was modified to produce singlet oxygen - a molecule that is visible under electron microscopy (EM) - whenever it was illuminated by blue light. Previously, such labelling techniques were only possible in traditional light microscopy, which is much less powerful than electron microscopy.
“We believe this can have a similar impact for electron microscopy as the Green Fluorescent Protein had for [light] microscopy,” said co-author Xiaokun Shu from the University of California at San Francisco.
The finding, said Shu, is a step forward in our ability to observe and investigate nano-scale cellular and sub-cellular structures.
'Lighting up' life
The amount of detail we can observe in cells depends on a microscope's resolution, which is limited by wavelength. Compared to traditional light microscopy, the resolving power of EM is greater because electrons have smaller wavelengths than light, and thus can achieve higher magnification.
Electron microscopes can then use a beam of electrons to create a highly detailed image of sub-cellular structures, while optical microscopes generally lose vital resolution when magnified to this point.
But towards the end of the 20th century, the advent of proteins or cells artificially 'lighting up' greatly expanded the experimental possibilities of much biological research. Tsien and colleagues - who would go on to win a Nobel prize for this research - discovered and developed the Green Fluorescent Protein gene, which could be inserted into certain regulatory sequences in a species' genome to categorise, label and observe real-time molecular behaviour.
Revitalising electron microscopy
Yet this advance had little implications for EM, as fluorescent proteins are only visible under the limited resolution of light microscopy.
Now, together with Nobel laureate Roger Tsien and colleagues from the University of California, Shu's research could have similarly revitalised the use of electron microscopy with the development of a visible genetic tag, called ‘miniSOG’.
As outlined in their paper published by PLoS Biology, the researchers re-engineered a protein from the Arabidopsis, a small flowering plant that absorbs blue light as an indication of how much sun it receives.
But instead of emitting the standard biochemical signals, Tsien and Shu modified the protein to change incoming blue light into green fluorescence and singlet oxygen, which is visible under EM. To make miniSOG easily visible, they similarly modified singlet oxygen production into a tissue stain that an electron microscope could easily identify.
