Slicing mitotic spindle with lasers, nanosurgeons unravel old pole-to-pole theory

The mitotic spindle, an apparatus that segregates chromosomes during cell division, may be more complex than the standard textbook picture suggests, according to researchers at the Harvard School of Engineering and Applied Sciences (SEAS).

The findings, which result from quantitative measurements of the mitotic spindle, appeared in the journal Cell, on Friday 27 April.

The researchers used a femtosecond laser to slice through the strands of the organelle and then performed a mathematical analysis to infer the microscopic structure of the spindle from its response to this damage.

"We've been using this nanosurgery technique to understand the architecture and assembly of the spindle in a way that was never possible before," says Eric Mazur, Balkanski Professor of Physics and Applied Physics at Harvard, who co-authored the study. "It's very exciting."

The spindle, which is made of protein strands called microtubules, forms during cell division and segregates chromosomes into the daughter cells. It was previously unclear how microtubules are organized in the spindles of animal cells, and it was often assumed that the microtubules stretch along the length of the entire structure, pole to pole.

Mazur and his colleagues demonstrated that the microtubules can begin to form throughout the spindle. They also vary in length, with the shortest ones close to the poles.