Developmental competence of oocytes grown in vitro: Has it peaked already?

Abstract

In vitro growth of immature oocytes provides opportunities to increase gametic resources and to understand the mechanisms underlying oocyte development. Many studies on the in vitro growth of oocytes have been reported thus far; however, only a few cases have been reported, which demonstrated that oocytes can support full-term development after in vitro fertilization. Our research group recently found that culture of mouse neonatal primordial follicles increased the birthrate; however, the establishment of an in vitro system that can completely mimic follicle or oocyte growth in vivo and control oogenesis remains an ongoing challenge.

Fig. 1.

Developmental competence of mouse oocytes grown in vitro from primordial follicles.

Fig. 2.

Development of embryos and offspring derived from a new 2-step culture system. A: Follicles cultured for 3 days on a Millicell membrane following isolation (i.e., day 13 of the total culture period). B: A follicle cultured for 14 days following isolation (at day 24 of the total culture period). C: Isolated cumulus cell-oocyte complexes (COCs) from cultured follicles at day 24. D: Expanded COCs after 17 h of in vitro maturation. E, F: Embryonic development after in vitro fertilization with BDF1 sperms: 2-cell embryos (E) and blastocysts (F). G: Offspring delivered by caesarean section at 19.5 days post coitum.