Using stem cell technologies, researchers generated human cells and human tissues in the embryos of pigs and cattle. Then they inserted rat stem cells that contained a gene for the pancreas into these mutant embryos. "This suggests that rats lack a gallbladder not because of an inherent genetic deficiency of rat cells," Wu said. Though the experiment with human stem cells was interrupted at 28 days, it remains the first reported case in which human stem cells have begun to grow within another species. This subset consists of scientists introducing human cells into animal embryos at a very early stage.

Source: CNN January 27, 2017 00:11 UTC