The role of germinal vesicle karyoplasm in the development of male pronucleus in the mouse

Abstract

Zona-free mouse ovarian oocytes from Swiss albino females were bisected into nucleate and anucleate halves at the germinal vesicle stage (1), shortly after germinal vesicle breakdown (GVBD) (2) and in metaphase I (3). Sister halves were cultured for 15–17 h (ser. 1, 2) or 6.5–7.5 h (ser. 3) and those in which the nucleate fragment extruded the first polar body, were fertilized with F 1(C57BL/10 × CBA/H) spermatozoa. After an additional period of culture lasting for 6–7 1 2 (1, 2) or 16–17 h (3) the cells were fixed and examined in whole-mount preparations. Intact oocytes recovered from follicles at the same stages as those used for bisection, and ovulated oocytes (both zona-free) served as controls. Nucleate fragments and intact ovarian oocytes were fertilized in 65% and in the majority of them sperm heads were transformed into pronuclei; no differences were observed between the three series in the rate of fertilization and development of pronuclei. In anucleate oocyte fragments development of male pronuclei took place only if the dissolution of germinal vesicle had occurred prior to bisection. It is concluded that in the mouse, the germinal vesicle material is essential for transformation of sperm nucleus into the functional male pronucleus.