Tubulin polymerization in unfertilized sea-urchin eggs induced by elevated temperature.

Spontaneous polymerization of tubulin was induced in unfertilized eggs of the sea urchins Lytechinus pictus and Strongylocentrotus purpuratus by warming to temperatures 10-12 deg. C above the normal environment for each species. Indirect immunofluorescence microscopy showed that over a period of several hours polymerization proceeded from a fine crystal-like precipitate to larger and fewer higher-order structures. These structures differed morphologically between the two species: L. pictus formed cytasters, while S. purpuratus most often formed flame-like arrays. Nuclear cycles were not initiated, permitting long-term observation of steady-state polymer redistribution. After several hours only a few very large cytasters remained near the surface of L. pictus eggs and these tended to constrict to form protrusions or occasionally a cleavage furrow that divided the egg into two fragments. Staining with rhodamine-labeled phalloidin showed that actin was also concentrated in the cytasters, primarily at the periphery of the centrosphere-like regions. L. pictus cytasters could be recycled by repeated cooling and rewarming, and showed an accelerated rate of polymerization with each successive cycle. Cytasters could also be isolated as long as the initial procedures were carried out at the elevated temperature. Washed preparations were stable at room temperature.(ABSTRACT TRUNCATED AT 250 WORDS)