Researchers have discovered a new way to tag and illuminate living cells and the insides of animals. By modifying a blue light-absorbing protein from a small flowering plant — Arabidopsis thaliana — scientists were able to produce fluorescent, three-dimensional images of microscopic objects via electron microscopes (EMs), measuring tens of nanometers.

The project — led by pharmacology professor Roger Tsien — follows in the vein of the professor’s work with green fluorescent proteins (GFPs) in light microscopy, for which he earned his 2008 Nobel Prize in chemistry

Project scientist Varda Levram-Ellisman said this technique provides more detail on microscopic objects than other techniques.

“It gives us superior results compared to other methods,” Levram-Ellisman said. “The results are much better for visualization and are much more precise; you can even see single peptide structures.”

According to Tsien, the use of the engineered protein — also known as “miniSOG” — is useful with electron microscopes. The miniSOG is also used to locate and identify proteins with implications for various diseases.

“This is a tool that can help address many questions,” Levram-Ellisman said. “It can answer questions of protein localization, how many times a protein appears in cells, [and] in terms of different diseases, you can see accumulation of proteins in specific places more than normal.”

The protein works as a genetic tag; it latches onto proteins and illuminates them to give details of localization and structure.

“The proteins of interest are carrying around the genetic tag, wherever it goes,” Levram-Ellisman said. “You can see it in its final location, you can sometimes see it where it’s degrading, or where it’s being generated.”

Using the electron microscope helps. Past methods did not yield a clear image of fluorescing proteins.

“Our new technique enables us to put beacons on just about any protein and get a snapshot of its location at the much higher resolution of EM,” Tsien said.

Researchers used a plant protein that absorbs blue light, which triggers a cascade of biochemical signals. They engineered it to change the blue light into green fluorescence and single oxygen molecules, which then produce a tissue stain.

To locate proteins, the researchers confirmed the use of the tag by illuminating and locating well-known proteins. Tsien and UC San Francisco pharmaceutical chemistry professor Xiaokun Shu tagged two neuronal proteins in mice and identified their location in the brain.