In vitro growth of the ovarian follicle: taking stock of advances in research.

Several factors are necessary for the growth and survival of healthy follicles in the folliculogenesis process, including endocrine and paracrine glands, and a regulated ratio of granulosa cells to oocytes. One of the most powerful methods for studying folliculogenesis is the culture of ovarian follicles and oogenesis within a completely controlled environment. Follicle culture systems are highly developed and are rapidly evolving. However, the methods for separating the follicles, the cultivation techniques, the culture medium, and the dietary and hormonal supplements vary depending on the species studied. This study made a literature review of follicular culture techniques, and we investigated the heterogeneity among these key variables in follicular culture.

Epidermal growth factor and three-dimensional scaffolds provide conducive environment for differentiation of mouse embryonic stem cells into oocyte-like cells.

Three-dimensional (3D) culture provides a biomimicry of the naive microenvironment that can support cell proliferation, differentiation, and regeneration. Some growth factors, such as epidermal growth factor (EGF), facilitate normal meiosis during oocyte maturation in vivo. In this study, a scaffold-based 3D coculture system using purified alginate was applied to induce oocyte differentiation from mouse embryonic stem cells (mESCs). mESCs were induced to differentiate into oocyte-like cells using embryoid body protocol in the two-dimensional or 3D microenvironment in vitro. To increase the efficiency of the oocyte-like cell differentiation from mESCs, we employed a coculture system using ovarian granulosa cells in the presence or absence of epidermal growth factor (+EGF or -EGF) for 14 days and then the cells were assessed for germ cell differentiation, meiotic progression, and oocyte maturation markers. The cultures exposed to EGF in the alginate-based 3D microenvironment showed the highest level of premeiotic (Oct4 and Mvh), meiotic (Scp1, Scp3, Stra8, and Rec8), and oocyte maturation (Gdf9, Cx37, and Zp2) marker genes (p < .05) in comparison to other groups. According to the gene-expression patterns, we can conclude that alginate-based 3D coculture system provided a highly efficient protocol for oocyte-like cell differentiation from mESCs. The data showed that this culture system along with EGF improved the rate of in vitro oocyte-like cell differentiation.