Researchers Produce Viable, Embryo Forming Egg Cells from Underdeveloped Oocytes - Video

Mature egg cells, or oocytes, are essential for fertilization in assisted reproductive technologies. However, some 'denuded' oocytes, or those lacking the protective granulosa cell layer, fail to mature. Now, in a new study by researchers at Shinshu University, the team has developed a method to culture mature oocytes from these denuded oocytes in the lab.

The study published online in Biology of Reproduction, Assistant Professor Kanako Morohaku and her team at Shinshu University have identified a novel method to produce viable, embryo-forming eggs from denuded oocytes taken from “preantral” follicles in mice.

The researchers isolated denuded oocytes and granulosa cells from mice, which were then grown together in a U-shaped lab dish for eight days. This led to the formation of granulosa cell-oocyte complexes, which allowed the oocytes to interact with supporting cells again. These oocytes were cultured with granulosa cells under high (20%) and low (5%) concentrations of oxygen to observe the difference in oocyte growth.

They observed that low oxygen levels significantly improved the development of granulosa cell-oocytes and stimulated the formation of transzonal projections, thin cellular connections necessary for oocyte growth. After eight days, these reassembled granulosa cell-oocytes were cultured on a collagen-coated membrane for four additional days, leading to the maturation of oocytes into fertilizable eggs.

To test their viability, the researchers fertilized the eggs and transferred 126 embryos into female mice, following which they obtained six live pups. “To the best of our knowledge, our new culture protocol is the first to successfully obtain offspring from preantral follicle-derived denuded oocytes grown by reconstructing granulosa cell-oocytes in vitro,” explains Mr. Tomohiro Kohama, a PhD student and one of the authors.

By enhancing the viability of denuded oocytes, this innovative approach could offer renewed hope for individuals facing infertility and contribute to the conservation of endangered species.

Reference: Tomohiro Kohama, Ikuo Tomioka, Kanako Morohaku, In vitro production of viable eggs from undeveloped oocytes in mouse preantral follicles by reconstructing granulosa cell–oocyte complexes, Biology of Reproduction, 2024;, ioae125, https://doi.org/10.1093/biolre/ioae125