Cross-species transplantation: generation of rat offspring from mouse ovarian oocytes

The idea of ​​maturing oocytes in the ovary and producing offspring has been realized in a variety of ways. One such method, ovarian transplantation, is a relatively simple procedure to obtain eggs compared to in vitro culture of ovaries and follicles. However, it remains difficult to transplant ovaries into cellular immunodeficient mice and produce offspring from eggs grown inside the mice.

To produce offspring from xenotransplanted ovaries, Japanese researchers from Niigata University and Toyama University conducted a study to establish a system to transplant rat ovaries into mice and produce offspring from the resulting eggs. .

Researchers transplanted rat ovaries under the kidney capsule of immunodeficient mice and determined their survival rates. They then administered hormones involved in oocyte development and succeeded in collecting mature rat eggs. These eggs were found to develop normally when fertilized in vitro and become embryos or offspring when implanted in rat uteruses.

Using the ovaries of rats that express fluorescent proteins throughout their bodies as donors produced rat offspring that express the fluorescent proteins. It has been confirmed that this genetic trait is passed on to the next generation. These results were published in Scientific Reports on August 29, 2024.

“Although there have been reports of obtaining eggs and embryos by xenotransplantation of ovaries into mouse recipients, there have been no examples of successful birth of offspring. In this study, we hope to overcome this difficult challenge and obtain fertilized eggs and embryos. We were able to produce offspring,” says Runa Hirayama, a graduate student at Toyama University.

The key to producing offspring using this method was to collect mature eggs from the transplanted ovaries. After administering hormones to the transplanted mice, both mature and immature eggs were obtained from the transplanted ovaries. Mature eggs could be fertilized immediately after acquisition, whereas immature eggs needed to mature before being fertilized.

In this study, the researchers found that the proportion of eggs that matured and produced offspring in vitro was very low, and that their maturity at the time they were collected from the ovary was important for improving birth rates. .

“This new offspring production system has the potential for the generation of genetically modified rats and could become one of the most effective methods of animal offspring production,” says Dr. Hiroaki Taketsuru from Niigata University. .

This result will not only facilitate the creation of genetically modified animals, but will also be applicable to the creation of all kinds of animal offspring and reproductive medicine.