EFFECT OF LOCAL APPLICATION OF 1-METHYLADENINE ON THE SITE OF POLAR BODY FORMATION IN STARFISH OOCYTE*

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Abstract
Mechanism by which the site of polar body formation is determined in starfish oocytes was investigated in relation to the action of 1-methyladenine (1-MeAde). Local staining with Nile Blue of Asterina pectinifera oocytes revealed that there exists a prospective site of polar body formation (PSPBF) on the nearest surface to the position of germinal vesicle. The site of polar body formation shifed to some extent from PSPBF toward the area locally applied with 1-MeAde, suggesting that the actual site of polar body formation is not determined yet at the germinal vesicle stage. Oocytes whose germinal vesicles had been shifted by centrifugation from PSPBF to the opposite surface before the commencement of germinal vesicle breakdown (GVBD) (less than 15 min after 1-MeAde treatment) failed to form polar bodies, whereas oocytes centrifuged after commencement of GVBD (20 min after 1-MeAde treatment) did form polar bodies where their fading germinal vesicles had reached by centrifugation. In oocytes which failed to form polar bodies by centrifugation, an aster was observed near PSPBF of each oocyte. When inseminated, every oocyte treated with 1-MeAde developed normally irrespectively of the mode of polar body formation including the site and the occurrence, and the animal pole of every larva was derived from PSPBF.