Abstract
When starfish oocytes were stained with an anti-α-tubulin antibody during polar body formation,
the spindle as well as the asters of the mitotic
apparatus (MA) were asymmetrical, whereas centrifugation
made the MA symmetrical and inhibited
polar body formation (Satoh, S.K. et al., Develop.
Growth & Differ., 36: 557-565, 1994). Asymmetry
in the mitotic spindle was induced by the attachment
to the cell surface during maturation in the
starfish oocyte. We analyzed fluorescence micrographs
of MA quantitatively in both intact and
centrifuged oocytes using NIH Image software.
Digital subtraction of images of two corresponding
half spindles revealed that the half spindles of the
intact MA were different in fluorescence intensity,
but those of the centrifuged MA were equal. In the
intact MA, the peripheral half spindle was brighter
by 18% and larger by 20% than the inner half
spindle. Consequently, the average ratio of fluorescence
intensity in the peripheral half spindle (near
the egg surface) to that in the inner half was 1.37.
When polar body formation was inhibited by centrifugation,
the ratio dropped to 1.02, i.e., both half
spindles fluoresced equally. These results demonstrate
clearly that MA during polar body formation
in the starfish oocyte is asymmetrical.
