Progesterone induction of oocyte maturation in Rana pipiens: Reversibility of cycloheximide inhibition

Abstract

AbstractThe reversibility of cycloheximide inhibition of progesteroneinduced oocyte maturation was investigated. Progesterone treated immature oocytes underwent nuclear (germinal vesicle breakdown) and cytoplasmic maturation unless inhibited by incubation in the continuous presence of cycloheximide. However, when previously treated oocytes were simply washed in culture media on the day following the initial treatment, they matured without additional exposure to progesterone. The incidence of germinal vesicle breakdown observed after washing and reincubation was similar to that seen in paired oocytes retreated with progesterone, cycloheximide‐pretreated control oocytes newly treated with progesterone or control oocytes treated only with progesterone on the first day. Oocytes exposed to low concentrations of progesterone matured the following day whereas paired oocytes inhibited by cycloheximide during the first day did not mature at similar low doses following washing on the second day. The time of germinal vesicle breakdown in oocytes previously inhibited with cycloheximide was either slightly delayed or unaltered as compared to that of control oocytes newly treated with progesterone. The results indicate that an initial step of progesterone induced maturation in Rana is reversibly blocked but not detrimentally altered by cycloheximide. The evidence suggests that the effects of cycloheximide may be mediated through effects on the formation and/or autocatalytic production of maturation promoting factor (MPF). The cellular and molecular significance of these data to the process of meiotic arrest and oocyte maturation are discussed.