The red spray pictured here may look like fireworks erupting across the night sky on July 4th, but it’s actually a rare glimpse of tiny protein strands called microtubules sprouting and growing from one another in a lab. Microtubules are the largest of the molecules that form a cell’s skeleton. When a cell divides, microtubules help ensure that each daughter cell has a complete set of genetic information from the parent. They also help organize the cell’s interior and even act as miniature highways for certain proteins to travel along.
As their name suggests, microtubules are hollow tubes made of building blocks called tubulins. Scientists know that a protein called XMAP215 adds tubulin proteins to the ends of microtubules to make them grow, but until recently, the way that a new microtubule starts forming remained a mystery.
Sabine Petry and her colleagues at Princeton University developed a new imaging method for watching microtubules as they develop and found an important clue to the mystery. They adapted a technique called total internal reflection fluorescence (TIRF) microscopy, which lit up only a tiny sliver of a sample from frog egg (Xenopus) tissue. This allowed the scientists to focus clearly on a few of the thousands of microtubules in a normal cell. They could then see what happened when they added certain proteins to the sample.
Petry and her team knew already that a special tubulin known as gamma-tubulin is necessary to form a new microtubule. However, it was only after they added XMAP215 as well as gamma-tubulin to the sample that they saw new microtubules form and grow, as shown in the video. It turned out that XMAP215 plays two roles in microtubule development—helping form new tubules and helping them grow longer. Petry’s co-author, Akanksha Thawani, a Princeton University graduate student, noted that understanding XMAP215’s double role may give scientists a way to precisely target errors in cell division and cytoskeleton assembly that underlie diseases such as cancer.
In parallel to Petry’s research, Fred Chang and his colleagues at the University of California, San Francisco, recently found that XMAP215 is critical for microtubule formation in living yeast cells, an important independent confirmation of XMAP215’s importance.
Petry’s research is supported in part by NIGMS through grants 1DP2GM12349301, 1F32GM119195-01 and 1F32GM119195. Chang’s research is supported in part by NIGMS through grants R01GM069670 and R01GM115185.