Gene expression in mouse ovarian follicle development in vivo versus an ex vivo alginate culture system

Ovarian follicle maturation results from a complex interplay of endocrine, paracrine, and direct cell-cell interactions. This study compared the dynamic expression of key developmental genes during folliculogenesis in vivo and during in vitro culture in a 3D alginate hydrogel system. Candidate gene expression profiles were measured within mouse two-layered secondary follicles, multi-layered secondary follicles, and cumulus-oocyte complexes (COCs). The expression of 20 genes involved in endocrine communication, growth signaling, and oocyte development was investigated by real-time PCR. Gene product levels were compared between i) follicles of similar stage and ii) COCs derived either in vivo or by in vitro culture. For follicles cultured for 4 days, the expression pattern and the expression level of 12 genes were the same in vivo and in vitro. Some endocrine (cytochrome P450, family 19, subfamily A, polypeptide 1 (Cyp19a1) and inhibin βA subunit (Inhba)) and growth-related genes (bone morphogenetic protein 15 (Bmp15), kit ligand (Kitl), and transforming growth factor β receptor 2 (Tgfbr2)) were downregulated relative to in vivo follicles. For COCs obtained from cultured follicles, endocrine-related genes (inhibin α-subunit (Inha) and Inhba) had increased expression relative to in vivo counterparts, whereas growth-related genes (Bmp15, growth differentiation factor 9, and kit oncogene (Kit)) and zona pellucida genes were decreased. However, most of the oocyte-specific genes (e.g. factor in the germline α (Figla), jagged 1 (Jag1), and Nlrp5 (Mater)) were expressed in vitro at the same level and with the same pattern as in vivo-derived follicles. These studies establish the similarities and differences between in vivo and in vitro cultured follicles, guiding the creation of environments that maximize follicle development and oocyte quality.