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Biol. Bull. 209: 21-30. (August 2005)
© 2005 Marine Biological Laboratory

Polar Body Formation in Spisula Oocytes: Function of the Peripheral Aster

Rafal M. Pielak, Christopher Hawkins, Aung Pyie, Jennifer Bautista, Kyeng-Gea Lee and William D. Cohen*

Department of Biological Sciences, Hunter College, New York, New York, and the Marine Biological Laboratory, Woods Hole, Massachusetts

* To whom correspondence should be addressed. E-mail: cohen{at}genectr.hunter.cuny.edu or bcohen{at}mbl.edu

Activated Spisula oocytes proceed through meiotic stages rapidly and in near synchrony, providing an excellent system for analyzing polar body formation. Our previous studies suggested that cortical spreading of the metaphase peripheral aster determines spatial features of the cortical F-actin ring that is generated prior to extrusion of the polar body. We tested this hypothesis by experimentally altering the number and cortical contact patterns of peripheral asters. Such alteration was achieved by (a) lovastatin-induced arrest at metaphase I, with and without hexylene glycol modification, followed by washout; and (b) cytochalasin-D inhibition of extrusion of the first polar body, with washout before extrusion of the second polar body. Both methods induced simultaneous formation of two or more cortically spreading asters, correlated with subsequent formation of double, or even triple, overlapping F-actin rings during anaphase. Regardless of pattern, ring F-actin was deposited near regions of greatest astral microtubule density, indicating that microtubules provided a positive stimulus to which the cortex responded indiscriminately. These results strongly support the proposed causal relationship between peripheral aster spreading and biogenesis of the F-actin ring involved in polar body formation.

Abbreviations: CD, cytochalasin-D • GVBD, germinal vesicle breakdown • HG, hexylene glycol • LV, lovastatin • PB, polar body • PB1 and PB2, first and second polar bodies






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