The experiments were done primarily to answer ethical criticism in the ongoing debate over stem cell research, which holds promise for developing treatments for diseases but has generated opposition because the embryo is destroyed when stem cells are retrieved.
One team, working at the Worcester, Mass.-based biotech company Advanced Cell Technology, created embryonic stem cells by removing a cell from a growing embryo without seeming to harm the embryo, reported the Boston Globe.
Another team, based at the Whitehead Institute for Biomedical Research in Cambridge, Mass., used another approach that involved genetic manipulations.
The teams worked separately, but the findings from both studies were published Sunday in the journal Nature.
Some specialists said neither alternative, in its current form, likely would be widely accepted because of the technical and ethical questions that remained, according to the Boston Globe.
The first new method still subjects a human embryo to a small risk, and the second involves deliberately creating an embryo with a disabled version of a gene that is crucial to normal development, reported the Washington Post.
The team disabled a gene, called Cdx2, in a skin cell taken from a mouse. That gene, normally not active in skin, governs the creation of the placenta during early embryo development, allowing the fetus to survive in the womb.
The team then fused the cell with a mouse egg whose own genetic material had been removed — a now commonplace cloning procedure that leads to the growth of an embryo in a lab dish, according to the Post.
Scientists are interested in embryonic stem cells because they have the ability to form any cell in the body, which helps research and could result in disease cures, but ethical questions arise over the creation of embryos for medical purposes.