Male cell leads to female birth…first successful ‘sex-reversed cloning’

For the first time ever, scientists have successfully used gene editing technology to transform male mice into female mice through a process known as "sex reversal cloning." Japanese researchers from Yamana Institute produced this groundbreaking result, sharing their findings in a pre-print collection via BioAkiba. The team hopes that their genetically engineered technique could be a new breakthrough for conserving species with critically low populations.

Professor Ishizuka Daisuke, who led the research, explained that this study challenges the long-held belief in biology that both male and female individuals are necessary for reproduction. In mammals, sex is determined by sex chromosomes: females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). Thus, the key factor in determining sex in mammals is the presence or absence of the Y chromosome.

The researchers were inspired by the unique situation of the Okinawa wormfish, a species where reproduction is impossible without males. To achieve this feat, the team first developed a genetic scissors called "Y-CUT" that precisely removes Y chromosomes during cell division. They then utilized a technique called "chromosome nuclear transfer" to replace the nucleus in a sperm cell of a male mouse with a nucleus lacking the Y chromosome from a female mouse's egg cell.

Remarkably, some of the resulting embryos developed into female mice with just one X chromosome (XO) instead of the typical XX. Despite lacking a Y chromosome, these female clones grew healthy and even possessed normal reproductive abilities, exhibiting identical genetic makeup to their male counterparts except for the absence of the Y chromosome.

The researchers also managed to create XO female clones from frozen male cells, demonstrating the technique's potential for long-term conservation efforts. Professor Ishizuka expressed his excitement, comparing the achievement to a science fiction movie scenario. The team anticipates numerous applications in wildlife conservation, such as using frozen sperm cells from a male individual to produce females and reproduce them in captivity.

However, the technique is not without limitations. It requires the presence of a "nuclear empty sperm cell" from the same or closely related species to successfully transfer the embryos. Additionally, in species where females are the only surviving individuals, this technology would be ineffective. Another concern raised by Dr. Linda Penfold, a senior scientist at the International Union for Conservation of Nature, is the potential ethical issues and reduced genetic diversity resulting from cloning.

She also expressed concern about the impact on the health of cloned individuals due to limited genetic variation. The researchers are currently investigating ways to address these challenges, such as inserting an X chromosome into the Y chromosome-depleted genome. Combining this approach with other recent techniques, such as the one reported by a team from Osaka University earlier this year, may help mitigate some of the identified issues.

If successful, these advancements could revolutionize the conservation of endangered species by enabling reproduction from a single male genome. However, the ethical implications of artificially manipulating the process of reproduction remain a concern, highlighting the need for further research and careful consideration of the potential consequences.