Efforts to extract eggs and spawn offspring from ovarian oocytes have been pursued for various purposes such as enhancing desirable traits in livestock and safeguarding human fertility. Ovarian transplantation is one of these techniques that has gained popularity and application. While the idea of transplanting ovaries from one species to another holds promise, the actual production of offspring remains a significant challenge. Researchers have created a groundbreaking method utilizing xenotransplantation (the transfer of organs between different species) that has led to the successful generation of offspring.
The concept of encouraging the development of oocytes within an ovary to yield offspring is being explored through various means. One notable approach is ovarian transplantation, which is a relatively straightforward method to obtain eggs, as opposed to the more complicated in vitro culture of ovaries and follicles. Nevertheless, achieving successful transplantation of ovaries into immunodeficient mice and generating offspring from the harvested eggs continues to be a significant hurdle.
To create offspring from xenotransplanted ovaries, researchers from Japan’s Niigata University and the University of Toyama conducted a study aimed at devising a system to produce offspring using eggs acquired from rat ovaries transplanted into mice.
The team positioned rat ovaries beneath the renal capsules of immunodeficient mice and confirmed their functionality. Subsequently, they administered hormones that support oocyte development, successfully retrieving mature rat eggs. These eggs developed properly when fertilized in vitro and were capable of developing into embryos or even offspring when placed in a rat’s uterus. Notably, using ovaries from rats that expressed a fluorescent protein led to offspring that also exhibited this fluorescent trait, confirming that this genetic characteristic was passed on to the next generation. These findings were published in Scientific Reports on August 29, 2024.
“While there have been accounts of acquiring eggs and embryos through interspecies ovarian transplantation into mice, no previous successful cases of producing offspring have been documented. In this study, we succeeded in creating fertilized eggs and actual offspring, overcoming a significant obstacle,” stated Runa Hirayama, a graduate student at the University of Toyama.
A key aspect of successfully generating offspring with this technique was the ability to retrieve mature eggs from the transplanted ovaries. After hormone treatment of the transplanted mice, both mature and immature eggs were collected from the transplanted ovaries. The mature eggs could be immediately fertilized, whereas immature eggs required further maturation prior to fertilization. The study revealed that the percentage of eggs cultured in vitro that matured and subsequently produced offspring was quite low, highlighting that the maturity of eggs when harvested from the ovary was crucial for enhancing the birth rate.
“This innovative system for producing offspring has significant potential for generating genetically modified rats and may emerge as one of the most effective strategies for animal reproduction,” asserts Dr. Hiroaki Taketsuru of Niigata University. This breakthrough not only promises to simplify the creation of genetically modified animals but can also be adapted for use in producing offspring across various animal species, as well as in the field of reproductive medicine.
