Premeiotic Aster as a Device to Anchor the Germinal Vesicle to the Cell Surface of the Presumptive Animal Pole in Starfish Oocytes

Abstract

The germinal vesicle (GV) of starfish oocytes stays just beneath the oocyte cortex at the presumptive animal pole during the long period of oogenesis. We subjected oocytes to a centrifugal force field to detach the GV from the cortex. The association between the cortex and the GV persisted and withstood a small amount of centrifugal acceleration at 200g. The GV was eventually separated from the cortex at 700g. The amount of acceleration sufficient for the GV separation was lowered when the oocytes were pretreated with Nocodazole and was increased by Taxol pretreatment. Observation of microtubular structures with an anti-α-tubulin antibody revealed the presence of a complex of spots and radiating arrays as was described by J. J. Otto and T. E. Schroeder (1984, Dev. Biol. 101, 274–281) and called the premeiotic aster. Nocodazole shortened the astral arrays, and Taxol enhanced them. These observations indicate that the premeiotic aster works as a device to hold the GV in an eccentric position just beneath the oocyte cortex.