The Washington Post reports that a leading University of Pittsburgh researcher on embryonic stem cells will leave a joint stem cell research team launched in collaboration with world-renowned cloning researcher Hwang Woosuk.

The American scientist, Gerald Schatten, who has worked with Hwang for more than a year, has reportedly raised ethical questions as to how the Korean cloning pioneer collected human eggs for the research.

The U.S. daily said that rumors spread that the eggs Hwang used had been taken from a junior scientist in his lab.

The post reported that, if true, it would be in violation of research ethics that forbid people in positions of authority from accepting egg donations from their subordinates.