Cytoplasmic cycle in meiotic division of starfish oocytes

Abstract

Nonnucleate fragments of sea urchin and amphibian eggs are known to show an autonomous cyclic activity whose interval is comparable to the cleavage interval of normal eggs. In order to examine for the presence of such a cytoplasmic cycle in meiotic division, maturing oocytes of the starfish, Asterina pectinifera, were bisected into halves about 10 min after germinal vesicle breakdown, and tension at the surface of the nonnucleate fragments was continuously measured by a compression method. The nonnucleate fragments were found to show cyclic changes in the tension, with a temporal pattern very similar to that of the changes accompanying the two successive meiotic divisions of normal oocytes; i.e., the sharp peak in the tension was found to occur always twice, and only twice. However, the nonnucleate fragment of immature oocytes showed only a gradual rise in the tension without any cyclic change even when it was induced to mature by 1-methyladenine. When the maturing oocyte was bisected before germinal vesicle breakdown, the nonnucleate fragment still did not cycle. These results indicate that cytoplasm of maturing oocytes which underwent germinal vesicle breakdown is endowed not only with cyclic activity, but also with terminating it after two cycles. It is suggested that germinal vesicle material may trigger such an autonomous cyclic activity.