Spindle microtubule dynamics following ultraviolet-microbeam irradiations of mitotic diatoms

Abstract

Lesions (ARB [areas of reduced birefringence]) generated in metaphase and anaphase central spindles of Hantzschia by a UV microbeam are devoid of microtubules previously present. In vivo, the poleward transverse edge of the lesion invariably loses birefringence poleward, until this segment has vanished; the loss is slow during metaphase and faster at anaphase. The other transverse edge, proximal to the overlap, remains stable until disassembly of the whole spindle. The central spindle microtubules are not in flux during metaphase to telophase, and depolymerization of these microtubules takes place only from the end distal to the pole, as during normal spindle disassembly. Microtubule polarity and the creation of free ends may determine which microtubules are disassembled during later mitosis and how disassembly proceeds.