title: FOXO3a is involved in the apoptosis of naked oocytes and oocytes of primordial follicles from neonatal rat ovaries.
abstract: Inhibition of the forkhead transcription factor, FOXO3a, can promote the transition from primordial to primary follicle and subsequent follicle development in mammalian ovaries. Stem cell factor (SCF) initiates anti-apoptotic signaling from its membrane receptor, c-kit, to Bcl-2 family members through PI3K/AKT in oocytes of primordial follicles. However, whether FOXO3a mediates the apoptosis of naked oocytes and oocytes of primordial follicles remains unknown. In the present study, oocytes from nests and primordial follicles from neonatal rat ovaries were cultured, and oocyte apoptosis was examined using the TUNEL technique. The pro-apoptotic action of FOXO3a and the potential signal transduction pathways were investigated using RT-PCR, Western blot, and immunocytochemistry. Culturing oocytes in the presence of SCF did not affect the level of total FOXO3a protein, but rapidly elevated the level of phosphorylated FOXO3a (indicating functional suppression). As phosphorylated FOXO3a increased, oocyte apoptosis was inhibited. The specific PI3K/Akt inhibitor, LY 294002, abolished the phosphorylation of FOXO3a and the anti-apoptotic action of SCF. SCF down-regulated the expression of p27KIP1 and pro-apoptotic factors such as Bim, Bad, and Bax, and this activity was reversed by LY 294002. SCF up-regulated the expression of MnSOD, which was also inhibited by LY 294002. However, SCF had no effect on Bcl-2 protein. These results suggest that FOXO3a is involved in oocyte apoptosis in the neonatal rat ovary, and the SCF-PI3K/Akt-FOXO3a signaling pathway mediates oocyte apoptosis and primordial follicle formation.
authors.affiliation: Shantou University Medical College, Shantou, Guangdong, PR China.
authors.forename: Hong
authors.initials: H
authors.lastname: Liu
authors.forename: Li-Li
authors.initials: LL
authors.lastname: Luo
authors.forename: Yuan-Shu
authors.initials: YS
authors.lastname: Qian
authors.forename: Yu-Cai
authors.initials: YC
authors.lastname: Fu
authors.forename: Xu-Xia
authors.initials: XX
authors.lastname: Sui
authors.forename: Yi-Jie
authors.initials: YJ
authors.lastname: Geng
authors.forename: Da-Na
authors.initials: DN
authors.lastname: Huang
authors.forename: Shi-Tong
authors.initials: ST
authors.lastname: Gao
authors.forename: Ren-Li
authors.initials: RL
authors.lastname: Zhang
mesh_terms: D000818:Animals; D017209:Apoptosis; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000378:metabolism; D005260:Female; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism / Q000502:physiology*; D006080:Ovarian Follicle / Q000378:metabolism / Q000502:physiology*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D019089:Stem Cell Factor / Q000378:metabolism; D013482:Superoxide Dismutase / Q000378:metabolism
chemical_list: C499515:FOXO3 protein, rat; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D019253:Proto-Oncogene Proteins c-bcl-2; D019089:Stem Cell Factor; D050760:Cyclin-Dependent Kinase Inhibitor p27; D013482:Superoxide Dismutase; D051057:Proto-Oncogene Proteins c-akt