Dynamics of Mitotic Apparatus Formation and Tubulin Content during Oocyte Maturation in Starfish

To follow the topo‐temporal behavior of structures containing tubulin and the change in tubulin content during oocyte maturation, starfish oocytes were extracted with a medium containing detergent so that morphological observation and biochemical analysis could be conducted on the same residual oocyte preparation simultaneously. Before 1‐methyladenine (1‐MeAde) stimulation, “pre‐meiotic asters” were observed on the germinal vesicle at the animal pole. 1‐MeAde caused the appearance of distinct asters at the position of the aster precursor. When germinal vesicle breakdown (GVBD) took place, chromosomes were condensed. Chromosome gathering was concurrent with a reduction in the size of nuclear matrix. The mitotic apparatus was first constructed parallel to the cortex and then changed its axis perpendicularly. Fluorescence of tubulin due to indirect immunofluorescence in the cytoplasm other than the mitotic apparatus decreased rapidly along the course of maturation at least up to the first metaphase. Despite these dynamic morphological change, the tubulin content in the whole oocyte and the residual structures, measured by SDS‐PAGE and immunostaining, did not show remarkable (statistically significant) changes through the course of maturation, although the content tended to decrease a little before the second polar body formation and to increase thereafter in the latter.