Maturation of mouse primordial follicles by combination of crafting and invitro culture

Cryopreservation of ovarian cortical tissue and subsequent transplantation or in vitro culture of follicles are technologies under development with th e aim to safeguard fertility in patients with gonadal failure. in the prese nt study, we investigated whether primordial follicles could be triggered t o full maturation by a combination of in vivo transplantation and in vitro culture in a mouse model. In a first step, newborn mouse ovaries containing only primordial follicles were allotransplanted under the renal capsule of ovariectomized recipient mice. The second step was to mechanically isolate growing preantral follicles from the graft and culture these in vitro to m aturity. In our experiment, one newborn mouse ovary was transplanted under the renal capsule of each 8- to 12-wk-old F1 (C57Bl/6j x CBA/Ca) female ova riectomized recipient (n = 26), Two weeks after transplantation, all 26 gra fts were recovered. Four grafts were professed for histology and showed tha t developmental stages of follicles in 14-day-old ovarian grafts were compa rable to those in 14-day-old mouse ovaries, The 22 remaining grafts were us ed for mechanical isolation of preantral follicles, As a control group, pre antral follicles isolated from ovaries of 14-day-old mice were used. The me an preantral follicle yield per ovary was II in the transplant group versus 33 in the control group. Follicles were cultured individually in 20-mu l d roplets of ol-MEM supplemented with 100 mIU rFSH and 5% fetal bovine serum for 12 days under an atmosphere of 5% CO2 in air at 37 degrees C. By Day 12 of culture, 66.5% of follicles retained their oocytes in the grafting grou p versus 97.5% in the control group (P < 0.001). Final oocyte maturation wa s induced by addition of 2.5 IU/ml hCG, At 14-16 h post-HCG, the percentage s of oocytes showing germinal vesicle breakdown and polar body extrusion we re significantly higher in the control group (90.6% and 82.8%) compared to the grafting group (60% and 45%). The mean diameter of the mature oocytes o f the grafting group (69.9 +/- 4.45 mu m) was similar to that of oocytes fr om the control group (70.5 +/- 2.35 mu m) Our results suggest that maturati on of mouse primordial follicles is feasible by combination of in vivo tran splantation and in vitro culture. This two-step strategy may be an attracti ve model for promoting the growth and maturation of primordial follicles fr om other species.