RELATIONSHIPS BETWEEN DISTRIBUTION OF TUBULIN-PARACRYSTALS, GRANULES STAINING WITH NEUTRAL RED AND CLEAVAGE ACTIVITY IN SEA URCHIN EGG-FRAGMENTS1,2

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Abstract
Unfertilized eggs of Japanese sea urchins (Temnopleurus toreumaticus and Hemicentrotus pulcherrimus) were separated by centrifugation into 2 fractions (nucleated light and enucleated heavy fragments) or 3 fractions (nucleated light, enucleated middle and enucleated heavy fragments). These fragments were stained with neutral red and then fertilized. Cleavage took place only in fragments containing cytoplasmic granules staining with neutral red: no cleavage occurred in fragment without these granules. When fragments of unfertilized eggs were incubated in a solution in sea water of 10-4 M vinblastine, a mitotic poison that specifically binds to tubulin, tubulin-paracrystals were found in all kinds of fragments, irrespective of whether they had stained granules and cleavage activity. The lack of cleavage activity in the fragment probably is not due to the absence of polymerizable tubulin molecules in the cytoplasm, but rather to other factors, such as the absence of granules staining with neutral red. There is no relation between the distribution of these granules and polymerizable tubulin, but a close relation between the number of stainable granules and cleavage activity. Quantitative analysis of tubulin molecules in the egg fragments is necessary for confirmation of this idea.