Structural effects of mercaptoethanol during mitotic block of sea urchin eggs

Abstract

Abstract 1. (1) The first visual effect of mercaptoethanol on dividing sea urchin eggs is a collapse of the asters and spindle into a central clear region containing many membranes and vesicles. 2. (2) Microtubules are present in blocked cells. Chromosomal microtubules and probably also aster microtubules shorten in the block, retaining the structure of a mitotic apparatus, but with decreasing spindle length and aster size. Radial orientation is retained around the aster centers. 3. (3) The ability of the centers to separate in the block increases as the blocking time approaches metaphase and appears related to the number of polymerized microtubules present at the time of the block. Centers separate with formation of vesicle and microtubule tracts between them. 4. (4) Mercaptoethanol apparently prevents the normal increase in the pool of available microtubule protein during mitosis, but does not prevent microtubule depolymerization or new polymerization from an existing pool, which may be derived in part from depolymerization of existing microtubules.