Beijing, China - Chinese researchers have successfully used complex embryonic stem cell engineering to create mice that have two fathers and successfully reached adulthood, according to research published on Tuesday.

Scientists had previously achieved the feat with bi-maternal mice, but attempts to create a healthy bi-paternal mouse with that reached adulthood had failed.

The new study, published in the journal Cell Stem Cell, describes how researchers led by Wei Li of the Chinese Academy of Sciences (CAS) in Beijing modified 20 key imprinting genes in "a strategy that effectively addresses the most severe developmental defects in bi-paternal embryos."

They also found that these edits led to stem cells with more stable pluripotency - a cell's ability to differentiate into other cell types.

"These findings provide strong evidence that imprinting abnormalities are the main barrier to mammalian unisexual reproduction," said Guan-Zheng Luo of Sun Yat-sen University in Guangzhou, in southern China.

"This approach can significantly improve the developmental outcomes of embryonic stem cells and cloned animals, paving a promising path for the advancement of regenerative medicine."

Researchers said that the approach still had limitations, with less than 12% of viable embryos reaching birth, and not all born reaching adulthood. Most of the mice that made it to adulthood had altered growth and a shortened lifespan and all were sterile, though they did exhibit increased cloning efficiency, according to researchers.

"Further modifications to the imprinting genes could potentially facilitate the generation of healthy bi-paternal mice capable of producing viable gametes and lead to new therapeutic strategies for imprinting-related diseases," said CAS's Zhi-Kun Li.

The scientists said that, despite the limitations, the achievement remains a big step forward, adding that next they aim to apply these approaches to larger animals, including monkeys.