Action of actinomycin and puromycin upon frog oocyte maturation.

In amphibians, as well as in other vertebrates, occytes start to mature under the action of hypophyseal gonadotropic hormones. (In this paper the term 'maturation' implies the transformation into ripe eggs of oocytes that have finished growing.) In the course of maturation the oocytes themselves and the follicle cells surrounding them undergo changes; the changes of these two cell types are not causally connected, their coincidence in time is easily broken in unfavourable conditions (Wright, 1945; Tchou-Su & Wang Yu-lan, 1958). As shown earlier (Dettlaff, Nikitina & Stroeva, 1964), hypophyseal gonadotropic hormones affect amphibian oocytes through the oocyte nucleus, the germinal vesicle. As a result of their action the nuclear sap of the germinal vesicle acquires the ability to induce cytoplasmic maturation (the property revealed by Delage on the oocytes of Asterias glacialis, 1899, 1901, and by Wilson on those of Cerebratulus lacteus, 1903). It is also well known that the presence of gonadotropin is required for oocyte maturation and ovulation only in the first part of maturation period (hormone-dependent maturation period). Shortly before disruption of the germinal vesicle membrane, the maturation processes acquire inertia and do not need further action of hypophyseal hormones (hormoneindependent maturation period). It is of importance here that the main changes during maturation (dissolution of the germinal vesicle membrane, changes in the cytoplasmic properties) occur during the hormone-independent period. This paper makes an attempt to clarify the nature of processes in the oocyte during the hormone-dependent period and to elucidate the action of the gonadotropin-changed nuclear sap upon the cytoplasm. With this aim specific inhibitors of RNA and protein synthesis were applied, namely actinomycin D (cf. Goldberg & Reich, 1964; Georgiev, 1965) and puromycin (cf. Nathans, 1964). Criteria of the maturation process were used which allowed correlation between metabolic changes produced by inhibition and the events of maturation.