A group of stem cell researchers has successfully created a bi-paternal mouse—an adult mouse with two male parents—using embryonic stem cell technology. Their findings, published on January 28, 2025, in the journal Cell Stem Cell, detail how they addressed significant obstacles in producing unisexual offspring in mammals by focusing on specific genes linked to reproduction.
Previous attempts to produce bi-paternal mice were unsuccessful beyond a certain developmental stage, as the embryos ceased to grow. The research team, headed by Wei Li from the Chinese Academy of Sciences (CAS) in Beijing, concentrated on imprinting genes that manage gene activity in various ways. “This research will help tackle numerous challenges faced in stem cell and regenerative medicine,” states Li.
Co-author Qi Zhou, also from CAS, adds, “The distinct features of imprinting genes have led researchers to view them as a vital obstacle to unisexual reproduction in mammals. Even when bi-maternal or bi-paternal embryos are artificially created, they often fail to develop correctly because of these genes.”
Earlier efforts to produce a bi-paternal mouse involved using ovarian organoids to generate oocytes from male pluripotent stem cells, which were then fertilized by sperm from another male. However, this method resulted in imprinting errors when chromosomes from the same sex were involved, causing serious developmental issues.
In the current study, the researchers individually modified 20 essential imprinting genes using various approaches, such as frameshift mutations, deletions, and adjustments in regulatory regions. Remarkably, these modifications not only enabled the creation of bi-paternal mice that occasionally reached adulthood but also improved the stability of stem cells’ pluripotency.
“These results strongly indicate that imprinting abnormalities are the primary barrier to same-sex reproduction in mammals,” points out co-author Guan-Zheng Luo from Sun Yat-sen University in Guangzhou. “This strategy can greatly enhance the developmental success of embryonic stem cells and cloned animals, offering promising prospects for regenerative medicine.”
However, the team acknowledges some limitations in their research. Only 11.8% of viable embryos developed to birth, and not all surviving pups reached adulthood due to growth issues. Most that did live into adulthood showed altered growth patterns and had shorter lifespans. Additionally, the adult mice were sterile, although their cloning efficiency was notably higher.
“Further adjustments to the imprinting genes may help in generating healthy bi-paternal mice capable of producing viable gametes, potentially leading to innovative treatment strategies for diseases linked to imprinting,” says co-author Zhi-Kun Li from CAS.
The research team plans to explore how changes to imprinting genes can improve embryonic development potential. They also hope to apply the experimental techniques used in mice to larger species, such as monkeys. However, they recognize that this would take significant time and effort, as the imprinting gene combinations in monkeys differ substantially from those in mice. It remains uncertain if this technology will eventually be used to address human diseases. The International Society for Stem Cell Research prohibits heritable genome editing for reproductive reasons, as well as the use of gametes derived from human stem cells for reproduction due to safety concerns.
