Effects of cytoplasmic components upon sperm aster development in Bufo arenarum eggs.

Bufo arenarum oocytes obtained during the winter period, presenting a metabolism similar to that of the differentiated tissues, are not able to form a sperm aster after spermatozoon injection. These oocytes may be considered immature, with respect to the state of their cytoplasm. In the present work, aster formation was induced in winter coelomic oocytes through injection of cytoplasm from summer oocytes, GTP, and EDTA. When winter oocytes received cytoplasm from summer oocytes, they became able to form asters. If the cytoplasm interchange was inverted, i.e., if the cytoplasm of winter oocytes was injected into summer oocytes, no modification of the capacity to form asters was detected. In addition, the injection of GTP into winter oocytes induced the formation of asters in up to 60% of the oocytes, while the chelation of Ca2+ with EDTA had no effect on aster formation. Winter coelomic oocytes behaved as oocytes during prophase even after germinal vesicle breakdown. From the above, it may be suggested that these oocytes cannot activate the microtubule organizing centers.