Figure 7. Egg apoptosis correlates with the phosphorylation of Ser128 of Bad.

(A) Oocytes were microinjected with a mRNA encoding Bad-GFP and one hour later incubated in the presence or the absence of the JNK inhibitor, SP600125, or microinjected with p21^Cip1 protein (Cip). They were then stimulated with progesterone (time 0). Egg proteins were analysed at the indicated times by immunoblot using antibodies against Bad, Ser128 (pS128), Ser112 (pS112) or Ser136 (pS136)-phosphorylated forms of Bad, and the active phosphorylated form of JNK (p-JNK). These data are representative experiments repeated on oocytes and eggs from at least three different females. (B) Regulation of apoptosis in unfertilized eggs. In the ovary, prophase oocytes are protected from apoptosis by an inhibited form of Bad phosphorylated at Ser112 and Ser136. At time of ovulation, the oocyte completes meiotic maturation. Bad becomes phosphorylated on Ser128 under the control of Cdk1 and JNK. During aging, the ovulated egg progressively accumulates increasing amounts of the Ser128 phosphorylated form of Bad that can ultimately trigger the death execution, unless fertilization occurs.