Three-dimensional reconstruction studies of mitotic spindle ultrastructure

The mitotic spindle is composed chiefly of microtubules (MTs) and functions to equally distribute the replicated chromosomes to daughter cells. Spindles are generated from an interaction between the spindle poles and kinetochores. The former are responsible for generating spindle MTs while the latter act as sites for attaching the chromosomes to the MTs. As noted by McIntosh the emphasis of most mitotic investigations is structural “because the spindle is a kind of machine, and numerous structural questions are obvious as one tries to understand a device which converts chemical energy into mechanical work.”During the course of our mitosis studies it was frequently necessary to reconstruct the three-dimensional (3D) ultrastructure of spindles from serial sections. To do this we utilized the STERECON system developed at the Albany HVEM facility. Briefly, prints of serial sections are enlarged to an optimum final magnification. For each section, profiles are drawn on clear plastic sheets outlining the chromosomes, mitochondria, and spindle MTs.