Almost everyone treats Christmas as the time to get away from regular work. Surprisingly, there are exceptions, such as Roger Tsien. This late biochemist would do an extra two weeks of uninterrupted research in his lab during Christmas. In one of his sojourns, he gifted the world the first electron micrographs—in color. His method used to create them will dramatically advance cell imaging.
Scientists use Electron Microscopy (EM) for magnifying objects up to 10 million times their original size. The technique makes use of accelerated electrons for the purpose. Conventional EM images are in gray scale, and scientists add color using computer graphics programs, once the images are recorded. Tsien and his colleagues modified the EM technique for directly incorporating color labeling into the images.
Along with co-workers Mark H. Ellisman and Stephen Adams, Tsien devised techniques for employing serial applications of various lanthanides or rare earth metals, which served as the labels. Along with this, the researchers used the EELS or electron energy-loss spectroscopy type of Ems. EELS is capable of differentiating among the lanthanides. It does this by measuring the differences in energy deflected or absorbed by each lanthanide from an electron beam.
For instance, for creating the color image of a cell organelle such as an endosome, the researchers had to stain the sample initially with a lanthanide called cerium. This made the sample appear green when viewed under EELS. After removing the excess cerium, they applied the element praseodymium. This targeted another protein within the sample, which EELS now registered as red. Now all that the scientists had to do was to overlay the green and red images onto a traditional gray scale EM image and create the composite image. The final image highlighted different distinct regions of the endosome with red and green color.
In the November issue of the publication Cell Chemical Biology, Tsien, along with his coauthors, has described their multicolor EM technique. Although the technique is still very new, scientists are using it to obtain new information about cell structure. For instance, regular light microscopy is incapable of showing protein movements with and between cells. With the new technique, scientists can now view cell components at a much higher level of detail.
For instance, until now, scientists had only a hypothesis about the fate of certain molecules since they are too small to be visible using light microscopes. EELS offered vibrant proof and confirmed the hypothesis. So far, scientists had only conjectured that certain CPPs or cell penetrating peptides were responsible for ferrying molecules as cargo into cells, and that the cells then took up these molecules into the interior of endosomes. With the praseodymium coloring one kind of CPP with a red label, scientists were able to verify their hypothesis, as the CPP visibly ended up inside the endosome. At the same time, another molecule, colored vivid green with cerium, ended up predictably at the endosomal surface.
Tsien’s death has deprived the world of further contributions to this transformative technique. However, the innovations will continue to inspire his co-workers and the newer generation of scientists. Tsien, as a fitting last gift to the scientific world, added color to electron microscopy to allow them to see more within cells.