An Anti-Apoptotic Role for Ornithine Decarboxylase during Oocyte Maturation

Ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine biosynthesis, is a non-redundant and essential gene in all eukaryotes. During mitotic cell cycle, ODC exhibits two activity peaks - one at G1/S transition and the second during G2/M transition. The physiological role of this cell cycle-dependent ODC activity dynamic is not clear. Previous studies have reported a significant elevation of ODC activity during Xenopus oocyte maturation, which resembles mitotic G2/M transition. In order to study the roles of ODC activity in the oocytes, we utilized antisense morpholino oligos (xODC mo) to inhibit ODC translation. We report here that xODC mo abolished ODC activity increase during oocyte maturation. XMOD mo-injected oocytes underwent germinal vesicle breakdown, emitted the first polar body and reached metaphase II, thus completing \"nuclear maturation\". However, the metaphase II oocytes exhibited high levels of reactive oxygen species and became apoptotic. When transferred to host frogs and subsequently ovulated, these eggs were fertilized but exhibited embryo fragmentation. Translation of ODC is therefore integral to \"cytoplasmic maturation\