Ralf Jungmann, Ph.D., now a postdoctoral fellow working with Yin at the Wyss Institute and Harvard Medical School, helped develop one of those super-resolution methods, called DNA-PAINT, as a graduate student. DNA-PAINT can create ultrasharp snapshots of up to three cellular workers at once by labeling them with different colored dyes.
To visualize cellular job sites with crews of dozens of cellular workers, Yin's team, including Jungmann, Maier Avendano, M.S., a graduate student at Harvard Medical School, and Johannes Woehrstein, a postgraduate research fellow at the Wyss Institute, modified DNA-PAINT to create a new method called Exchange-PAINT.
Exchange-PAINT relies on the fact that DNA strands with the correct sequence of letters, or nucleotides, bind specifically to partner strands with complementary sequences. The researchers label a biomolecule they want to visualize with a short DNA tag, then add to the solution a partner strand carrying a fluorescent dye that lights up only when the two strands pair up. When that partner strand binds the tagged biomolecule, it lights up, then lets go, causing the biomolecule to "blink" at a precise rate the researchers can control. The researchers use this blinking to obtain ultrasharp images.
They then repeat the process to visualize a second target, a third, and so on. Then they overlay the resulting images to create a composite image in which each biomolecule each cellular worker -- is assigned a different color. This allows them to create false-color images that simultaneously show many types of biomolecules far more than they could simultaneously visualize by labeling them with different colored dyes. And these false-color images allow them to spot enough cellular workers at once to capture the entire scene.
To test Exchange-PAINT, the researchers created 10 unique pieces of folded DNA, or DNA origami, that resembled the numerals 0 through 9. These numerals could be resolved
|Contact: Dan Ferber|
Wyss Institute for Biologically Inspired Engineering at Harvard