Organization of cytoplasmic microtubules during maturation of goldfish oocytes

The organization of cytoplasmic microtubules during hormone-induced meiotic maturation of goldfish oocytes in vitro was examined by confocal immunofluorescence microscopy using an anti-tubulin antibody. The microtubule network was well distributed in fully grown immature oocytes. Once goldfish oocytes resumed meiotic maturation by a proposed maturation-inducing hormone of this species (17γ, 20β-dihydroxy-4-pregnen-3-one, 17α, 20β-DP), cytoplasmic microtubules serially re-organized. Soon after the onset of the germinal vesicle (GV) migration towards the animal pole, the former microtubule network disappeared, followed by the appearance of a long perinuclear tail with high ordered microtubules extending from the vegetal surface of the GV. Incubation of fully grown immature follilces in colcemid, an inhibitor of tubulin polymerization, caused the disappearance of microtubules. However, this treatment did not prevent either the 17α, 20β-DP-induced migration of the GV or GVBD. Coincident with the breakdown of the GV (GVBD), numerous microtubules intruded into the GV from its vegetal surface. Soon after GVBD, a disk-shaped ring consisting of microtubule asters and a small ring with a radial array of microtubules in its center was observed at the animal pole region. In mature oocytes with meiotic spindles at the animal pole surface, cytoplasmic microtubules were concentrated in a small region around the animal pole showing complicated microtubule arrays. The results presented define distinct changes in microtubule organization during the 17α, 20β-DP-induced meiotic maturation of goldfish oocytes.