Resumption of meiosis-I tissue to enucleated preovulatory oocytes: a preliminary report

Purpose : Ovarian tissue banking may be the best strategy to preserve female fertility. But optimal method to obtain viable mature oocytes remains challenging. In order to bypass the long in vitro oocyte growth period, we developed this study to test whether reconstruction of thawed primordial oocytes with enucleated preovulatory germinal vesicle (GV) oocytes could induce dictyate nuclei to undergo chromosomal condensation and meiotic maturation. Methods : Isolated primordial oocytes from thawed mouse ovarian tissue were reconstructed with enucleated GV oocytes. After electrofusion and in vitro maturation, the reconstituted oocytes were assessed for first polar body extrusion, cytoskeleton configuration, and chromosome abnormalities. Results : Primordial oocytes from thawed ovarian tissue showed a high survival rate. Following transfer and electrofusion, they could be fused with enucleated GV oocytes (35.6%, 36/101) and extruded a first polar body (52.8%, 19/36). These mature oocytes showed a normal spindle configuration and chromosome number. Conclusions : We successfully established a mouse cell model to prove that omitting the whole growth and maturation period by transfer of primordial oocytes to developmentally older enucleated oocytes would bypass the long growth period required to the preovulatory stage. Polar body extrusion could also ensue after in vitro growth. This study provided an alternative approach for future investigations in oocyte maturation.