It's about as long as the width of a human hair and only half that length across. So it's tiny - measured in millionths of a meter - and extremely tricky to manipulate. But the meiotic spindle plays so irresistibly important a role in separating our chromosomes during cell division that scientists are compelled to try to study it.
Now researchers at The Rockefeller University and colleagues in Japan have devised a contraption sensitive enough to probe and ply these microscopic spindles and have used it to measure for the first time the structure's stiffness and deformability. The findings, published last month in Nature Methods, are the culmination of four and a half years of refinements.
"It's a bit of a trick, but it works out. You can catch the spindles," says Tarun Kapoor, head of the Laboratory of Chemistry and Cell Biology at Rockefeller. "Now we've probed the mechanical architecture of the structure as a whole." To capture and manipulate the spindles, Kapoor and colleagues developed a system of two tiny, plate-like cantilevers mounted underneath the lens
of a microscope that can be maneuvered with micromanipulators to sandwich the elusive structures. One of the cantilevers is stiff; the other is an ultra-thin sensor (called a piezo-resistive strain sensor) that measures the spindle's response to forces when the distance between the two cantilevers is reduced to compress the spindle.
During cell division, meiotic spindles tease apart chromosomes to opposite ends of a cell and ensure that each daughter cell inherits the correct genetic information. Scientists have studied many biochemical interactions required for chromosome segregation but know much less about its mechanical properties - the actual forces exerted on and by the players involved. Kapoor and colleagues determined that the forces strong enough to bend but not break meiotic spindles were in the nanoNewton range (about one billionth of the force of Earth's gravity on an average-sized apple).