Surpassing all expectations, a mouse born from two males has astonished scientists.

Scientists from China have successfully created a mouse without a biological mother, marking a breakthrough in genetic research based on years of advancements in stem cell engineering. A key aspect of this experiment was that, despite having only two fathers as its genetic sources, the animal managed to reach adulthood, highlighting an important milestone in this type of practice and demonstrating its viability to researchers, as reported by ScienceAlert.

In the study led by molecular biologist Zhikuan Li from the Chinese Academy of Sciences, the researchers employed cutting-edge genetic modifications to create viable mice with two fathers. While previous attempts to produce embryos from male stem cells resulted in severe developmental defects or non-viable offspring, this latest method yielded healthier mice, albeit with a lower survival rate—only about 13 percent of embryos survived to birth, and half of them did not reach adulthood.

In natural mammalian reproduction, sperm fertilizes an egg, creating an embryo with two sets of genes. However, when both genetic contributions come from sperm, a phenomenon known as imprinting anomalies can occur. This leads to a double silencing effect, where both copies of a gene are mistakenly turned off, resulting in developmental issues. To overcome this challenge, Li and his team modified 20 imprinting genes using precise genetic techniques, such as gene deletion and editing specific regions.

Their success reflects progress in understanding congenital disorders and may have implications for future reproductive technologies that could also benefit humans. This is not the first instance of two-father reproduction in mice. In 2023, Japanese researchers achieved a similar outcome, although their method yielded only 1.1 percent successful births. In contrast, the Chinese approach significantly improved survival rates, even though the resulting mice remained sterile.

In contrast, Japanese scientists managed to create mice with two mothers back in 2004—a process that is inherently simpler since, in some species, eggs can develop in the body without sperm. However, in mammals, the absence of an egg presents unique challenges due to its crucial role in early development.

To navigate these hurdles, the researchers derived egg-like cells from male embryonic stem cells and fertilized them with sperm from another male. Prior to fertilization, they meticulously modified the imprinting genes to prevent harmful silencing effects. Although the mice proved to be healthier than their predecessors, the researchers acknowledge that further refinements are needed to enhance viability and fertility.

"Further modifications of imprinting genes could potentially lead to the production of healthy biparental mice capable of generating viable gametes and result in new therapeutic strategies for treating imprinting-related diseases," says Zhikuan Li. His research, published in the journal Cell Stem Cell, provides valuable insights into reproductive biology and genetics; however, the application of such technologies in humans is still far from realization. The complexity of imprinting genes in humans and the ethical concerns surrounding genetic modifications pose significant challenges for such endeavors.

Nonetheless, an important takeaway from this study is the potential application of studying imprinting genes for treating imprinting-related disorders in humans, such as Prader-Willi and Angelman syndromes. Both conditions arise from improper genetic imprinting and lead to severe developmental disabilities and neurological disorders.