Distribution of the Germinal Vesicle Material during Progesterone‐Induced Oocyte Maturation in Xenopus and in Cynops

Abstract

The distribution of the germinal vesicle material in the oocyte during progesterone-induced maturation was studied in Xenopus and in Cynops. In both species, 2 distinctive masses of yolk-free cytoplasm appear in specific areas of the oocyte and at definite stages of maturation. One, the primary cytoplasmic mass, is formed at the basal side of the germinal vesicle during early maturation and is very RNA-rich. In Xenopus, a large part of the primary cytoplasmic mass persists as a mass during maturation and ends up as a thin disk at the boundary between the animal and the vegetal hemisphere in the mature oocyte. In Cynops, a rod-like primary cytoplasmic mass extends near to the equatorial zone and becomes indistinct in the mature oocyte. The other, the secondary cytoplasmic mass, is formed at or prior to germinal vesicle breakdown in areas around the germinal vesicle and is also RNA-rich. The secondary cytoplasmic mass is dispersed and constitutes the RNA-rich animal hemisphere cytoplasm in the mature oocyte. Evidently, the primary and the secondary cytoplasmic mass contain different germinal vesicle materials.