Derivation of developmentally competent oocytes by the culture of preantral follicles retrieved from adult ovaries: maturation, blastocyst formation, and embryonic stem cell transformation

Objective To determine whether the preantral follicles in adult ovaries can generate developmentally competent oocytes after in vitro culture. Design Prospective, animal-model study. Setting Gamete and Stem Cell Biotechnology Laboratory, Seoul National University, Seoul, Korea. Animal(s) B6CBAF1 mice. Intervention(s) Preantral follicles collected from 8-week-old mice were cultured in vitro. Main Outcome Measure(s) Follicle development, embryogenesis, and embryonic stem cell characterization. Result(s) A mean of 50.3 preantral follicles were retrieved from one adult animal, which is significantly less than the number (88.7 follicles) retrieved from a prepubertal female. Extension of the culture period greatly improved oocyte maturation; increased follicular growth to the pseudo-antral (89%–91% vs. 32%) or mature oocyte stage (65%–77% vs. 13%) was observed after 12 or 13 days of culture compared with 9 days of culture. Blastocyst formation after parthenogenesis was detected in only one case; in comparison, the use of IVF yielded a large number of embryos that developed into blastocysts. A mean of 14.7 intrafollicular oocytes per animal were produced after 13 days of culture, and 41% of those developed into blastocysts after IVF. Embryonic stem cell–like colonies were established by subculturing the inner cell mass cells from the blastocysts. Conclusion(s) Developmentally competent oocytes can be generated by culturing adult preantral follicles. These results may help increase the feasibility of follicle culture systems.