Pre-culture with transferrin-Fe3+ before in vitro maturation improves the developmental competence of porcine oocytes matured in vitro.

Purpose: Since the developmental competence of oocytes cultured after in vitro maturation (IVM) is low, it is necessary to improve the IVM method for efficient offspring production. In this study, we revealed that transferrin (TF)-Fe³⁺ was accumulated in follicular fluid with increasing the follicular diameter, and that TF receptor (TFR1) was localized in granulosa cells of pig. Thus, we hypothesized that TF-Fe³⁺ would be a factor in the induction of developmental competence of porcine oocytes.

Methods: To mimic the follicular development environment, cumulus-oocyte complexes (COCs) were cultured in pre-IVM medium (low dose of FSH) without or with Holo-TF (monoferric or diferric TF) or Apo-TF (non-iron bond TF). After pre-IVM without or with Holo-TF, COCs were cultured in IVM medium (high dose of FSH and EGF) without or with Holo-TF.

Results: Cultivation with Holo-TF increased the expression of follicular development maker (Cyp19a1 and Ccnd2), E2 production, and proliferative activity of cumulus cells, whereas cultivation with Apo-TF did not show these positive effects. The treatment with Holo-TF during pre-IVM, but not during IVM, dramatically induced oocyte maturation with increasing the blastocyst rate.

Conclusion: We succeeded in showing for the first time that the cultivation with Holo-TF in pre-IVM can produce embryos in pig with high efficiency.