What Forms Spindle Fibers During Mitosis?

What Forms Spindle Fibers During Mitosis? At the beginning of nuclear division, two wheel-shaped protein structures called centrioles position themselves at opposite ends of the cell forming cell poles. Long protein fibers called microtubules extend from the centrioles in all possible directions, forming what is called a spindle. What produces spindle fibers for mitosis? Microtubules