The R Ole of the Germinal Vesicle in Ooecyte Maturation in Anurans as Revealed by the Removal and Transplantation of Nuclei.

A STUDY of nucleo-cytoplasmic interactions in pre-embryonic development, at maturation stages in particular, is of great interest. During this period ooplasmic segregation takes place, specific properties of the cortex arise, and the cytoplasm obtains information from the oocyte nucleus which promotes the development of the embryo during all the changes related to fertilization, cleavage and blastulation (Wilson, 1925; Raven, 1961; Brachet, 1957, 1960; Briggs & King, 1959; Neyfakh, 1962). The first data on the role of the oocyte nucleus (germinal vesicle or GV) in cytoplasmic maturation were obtained by Delage (1899, 1901) on the starfish Asterias glacialis, and by Wilson (1903) on the nemertine Cerebratulus lacteus. In both species oocytes are expelled by the female before the GV dissolves, and mature in sea water. This allowed Delage and Wilson to experiment with oocytes at different maturation stages. They showed that anuclear fragments obtained by shaking the oocytes at the stage before GV dissolution did not reach maturity and could not be fertilized, although nucleated fragments could. All parts of oocytes fragmented immediately after GV dissolution mature, both those containing the nucleus (at the stage of the metaphase of the first cleavage division), and those lacking it. The same differences in the stage of the cytoplasm of Cerebratulus oocytes were found before and after GV dissolution with respect to the ability of the cytoplasm to form cytasters under the action of salts (Yatsu, 1905). From his experiments Delage drew the very important conclusion that cytoplasmic maturation requires the passage of the nuclear sap from the germinal vesicle to the cytoplasm. Delage made an attempt to elucidate the nature of the effect of the nuclear sap upon cytoplasmic maturation but at that time the level of knowledge in this field was inadequate for the solution of this problem.