The developmental potential of mouse oocytes matured in serum-free culture conditions

Abstract

Studies were undertaken to identify serum-free conditions for the maturation of mouse oocytes in vitro. Oocytes were recovered from the antral follicles of juvenile mice 48 h after injection with gonadotrophin and allowed to resume meiosis in modified Ham's F-10 (mHF-10) medium unsupplemented or supplemented with bovine serum albumin (BSA), fetal calf serum, human pre-ovulatory serum, human follicular fluid or EDTA. They were inseminated 14–16 h later, scored for polar body extrusion after 4–6 h with spermatozoa, and transferred to protein-free mHF-10 for further development. In-vivo matured ova were inseminated and cultured in parallel as controls. Fertilization and development were scored as two cells 24 h after insemination and blastocysts 4 days following insemination respectively. Surprisingly, 41% of oocytes cultured in unsupplemented mHF-10 completed meiosis I, and of those, 50% fertilized; serum supplementation did not improve maturation or fertilization rates. Although the addition of human follicular fluid to the mHF-10 improved meiosis (69%) and fertilization (68% of eggs with polar bodies) to levels comparable with the in-vivo control eggs (79 and 66% respectively), BSA supplementation was equally beneficial. Blastocyst development varied, but within each maturation/ fertilization group, the development from in-vitro matured eggs was comparable with embryos from in-vivo matured eggs. In addition, two out of eight 4-cell embryos from oocytes cultured in mHF-10 with BSA and EDTA gave rise to apparently normal pups following transfer to pseudopregnant recipients. Thus, gonadotrophin-stimulated mouse oocytes can complete meiosis and fertilize in culture in the absence of serum or follicular fluid. Oocytes cultured overnight in mHF-10, supplemented with EDTA and BSA, complete meiosis I, fertilize and develop to blastocysts at rates comparable with eggs matured in vivo. Serum-deprived oocytes have the potential to give rise to live offspring.