Oocyte Maturation in Chaetopterus pergamentaceous Observed With Centrifuge Polarizing Microscope

Premeiotic aster as a device to anchor the germinal vesicle to the cell surface of the presumptive animal pole in starfish oocytes

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 200 g. The GV was eventually separated from the cortex at 700 g. 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-alpha-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.

Windows to dynamic fine structures, then and now

How can we learn about dynamic fine structures that are far too small to be resolved with the light microscope without destroying the active living cell? Examples spanning the last half century show how polarized light microscopy can-and should-continue to provide an attractive window for such studies. Long before microtubules were found with electron microscopy, or their assembly properties were biochemically characterized in isolated cell-free systems, the dynamic fine structure of the mitotic spindle and assembly properties of its microtubules were revealed in living cells by polarized light microscopy. More recently, the polarizing microscope was improved, by invention of the new Pol-Scope, so that quantitative measurements of bire-fringence retardation and axes could be made rapidly for all image pixels independent of their birefringence axis orientation. In addition, the centrifuge polarizing microscope, just developed, allows us to follow the dynamic ordering of fine structures in living cells as they become stratified or restructured by centrifugal acceleration of up to ten thousand times gravity. The significance of these technological advances is discussed-Inoué, S. Windows to dynamic fine structures, then and now.