Probing the mechanical architecture of the vertebrate meiotic spindle.

Accurate chromosome segregation during meiosis depends on the assembly of a microtubule-based spindle of proper shape and size. Current models for spindle-size control focus on reaction diffusion-based chemical regulation and balance in activities of motor proteins. Although several molecular perturbations have been used to test these models, controlled mechanical perturbations have not been possible. Here we report a piezoresistive dual cantilever-based system to test models for spindle-size control and examine the mechanical features, such as deformability and stiffness, of the vertebrate meiotic spindle. We found that meiotic spindles prepared in Xenopus laevis egg extracts were viscoelastic and recovered their original shape in response to small compression. Larger compression resulted in plastic deformation, but the spindle adapted to this change, establishing a stable mechanical architecture at different sizes. The technique we describe here may also be useful for examining the micromechanics of other cellular organelles.