A mentor of embattled scientist Haruko Obokata, now at the center of a research controversy, took responsibility on April 16 for inadequately supervising her on their research project on stem cells that was once hailed internationally as groundbreaking.
However, Yoshiki Sasai, deputy director of the Riken Center for Developmental Biology (CDB) in Kobe, said at a news conference in Tokyo that he believes in the existence of the "stimulus-triggered acquisition of pluripotency" (STAP) phenomenon.
"(The existence of STAP cells) cannot be explained without the precondition of the STAP phenomenon," he said.
Sasai apologized for the controversy surrounding the research, which led to two highly touted articles that appeared in the prestigious British science journal Nature in late January. Sasai was one of the co-authors.
Obokata, 30, heads a research unit at the CDB, and Sasai, 52, was asked to join the project in the final writing stage. However, doubts arose about the veracity of the research and questions were raised about the images she used.
The Riken national research institute conducted an investigation into the STAP research and concluded Obokata had doctored and fabricated images used in the Nature articles. The other co-authors were absolved of wrongdoing, but Sasai was among those at Riken who were criticized for inadequate supervision of Obokata during the research project.
"I sincerely apologize for causing major confusion, misunderstanding-induced concerns and doubts over the articles," Sasai said at the news conference.
At the same time, Sasai explained that he only became involved in the articles in the final rewriting stage. That meant that he did not have access to the raw data generated during the experiment phase.
He said the division of labor in the structure that led to the writing of the Nature articles was unusual because different individuals were in charge of the four main stages of the research process. He also pointed out that Charles Vacanti, a Harvard University professor who was one of the co-authors, was in the United States during the research and writing stage.
He reiterated his past comment that the articles should be retracted because the reliability of the research had been called into question.
Sasai is one of three co-authors who have proposed retracting the Nature articles. Obokata has refused to go along, saying the STAP mechanism is a reality and there was no fabrication of images, but only a "mix-up."
Sasai became a professor at Kyoto University at age 36 and he is considered a leading expert on research into pluripotent cells. He has authored a number of articles related to his research. At the news conference, Sasai said that his experience in submitting articles to Nature was a major reason he was asked to join the rewriting of the articles, which had initially been rejected by the science journal.
However, the Riken investigation pointed to a number of shortcomings on Sasai's part in the STAP research. The investigative report said he bore major responsibility for failing to confirm the validity of the research data before submitting the articles to Nature. Questions have also been raised about why he failed to detect the doctoring of the images used in the articles and whether he looked over the research notes kept by Obokata.
At the news conference, Sasai explained that although he was senior to Obokata, she was in charge of her own research unit and was not his direct subordinate, so he could not simply summon her to his office as if she were a graduate student and ask to see her research notes and other data.
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