Healthy mice born from eggs derived from granulosa cells

Dec. 26 (UPI) -- Scientists have successfully birthed mice from eggs derived from granulosa cells, the cells that surround oocytes, or immature eggs.

Researchers described their feat this week in the journal Cell Reports.

Oocytes are the primary component of ovarian follicles, and granulosa cells support ovarian follicle health. Previous studies have shown granulosa cells possess plasticity similar to the shape-shifting abilities of stem cells. For the new study, scientists induced the granulosa cells to become oocytes.

"The thing about in vitro fertilization is that they only use the oocyte for the procedure," Lin Liu, senior author of the new study and a researcher with the College of Life Sciences at Nankai University in China, said in a news release. "After the egg retrieval, the granulosa cells in the follicle are discarded. It got us thinking, what if we can utilize these granulosa cells? Since every egg has thousands of granulosa cells surrounding it, if we can induce them into pluripotent cells and turn those cells into oocytes, aren't we killing two birds with one stone?"

In the lab, scientists used a pair of biochemical tools, a so-called ROCK inhibitor and crotonic acid, to turn granulosa cells into pluripotent stem cells. Granulosa cells typically die when separated from ovarian follicles, but the ROCK inhibitor helped cell death.

A combination of other chemicals encouraged the cells transformation into germline-competent pluripotent stem cells.

"It's a surprising result," said Liu. "The competency of induced pluripotent germline is usually lower than embryonic stem cells. Germline competency is crucial for germline cells to transfer genetic information to the next generation. With the co-formulation of Rock inhibitor and crotonic acid, it's not only more efficient, but the quality also increased."

Researchers subjected the transformed cells to another round of ROCK inhibitor and vitamin C to help stabilize the cell's genetic-replication abilities and turn the germline cell into a serviceable egg. Finally, scientists successfully impregnated the transformed cells and birthed anatomically normal mouse pups.

"This is the first time we turned granulosa cells into oocytes, it is a crucial and interesting work in developmental and reproductive biology," Liu said. "But implementing this research to humans from mice still has a long way to go. I think it has more prospect in preserving fertility and endocrine function, than in treating infertility."