In vitro culture of ovarian follicles
In mammals, the total number of oocytes that can ovulate is already determined in the fetal stage. Some of them develop in each sexual cycle (estrous cycle and menstrual cycle) after the puberty onset, leading to ovulation. The number of oocytes that lead to ovulation is only a fraction of the total number of oocytes in the ovary, even after superovulation induction. If we can efficiently develop and mature these follicular oocytes in vitro, we can use them effectively.
In livestock, "ovaries from slaughterhouses " are often used as a resource for obtaining oocytes. Oocytes are mainly extracted from developed follicles (antral follicles) that already exist in the ovary, matured in vitro, and used for in vitro fertilization. In addition, if undeveloped intrafollicular oocytes in the ovary can be used, we will obtain oocytes in a very efficient manner. Therefore, studies have been conducted on experimental animals and livestock to develop undeveloped ovarian follicles in vitro in order to form antral follicles.
In the mouse, there is a transient follicular development (so-called the first wave of folliculogenesis) before puberty, and this synchronized follicle formation has been studied (Ref. 1). Furthermore, primitive ovarian follicles immediately after birth can be cultured by a two-step culture method, and litters derived from oocytes in the cultured follicles have been obtained (Ref. 2).
References
- Eppig, J. J. and A. C. Schroeder (1989): Capacity of mouse oocytes from preantral follicles to undergo embryogenesis and development to live young after growth, maturation, and fertilization in vitro. Biol. Reprod. 41(2): 268-76.
- Eppig, J. J. and M. J. O'Brien (1996): Development in vitro of mouse oocytes from primordial follicles. Biol. Reprod. 54(1): 197-207.