KOBE – Yoshiki Sasai, a co-author of controversial research papers on so-called STAP cells, committed suicide at an institute of the government-affiliated Riken in Kobe, police said Tuesday.
Sasai, 52, deputy director of the Riken Center for Developmental Biology in Kobe and an adviser to scandal-hit Riken scientist Haruko Obokata, 30, was confirmed dead after being found hanged from a stairway handrail at the center, the police said.
He was wearing a short-sleeve shirt and a pair of slacks. His shoes were off, placed together on the landing of the staircase.
Satoru Kagaya, head of public relations at Riken, said at a news conference that at least one apparent suicide note was found on the desk used by Sasai’s secretary, as well as three other notes left near the body.
One of the notes, addressed to Obokata, read, “Be sure to reproduce STAP cells,” sources revealed later in the day.
Kagaya said earlier he could not disclose to whom the suicide notes were addressed, “considering the deep sorrow that Sasai’s family must be feeling at this point.”
Kagaya noted that when he talked to Sasai over the phone several times in May and June, he seemed to have been “tired both mentally and physically.” Kagaya said he felt something was wrong in the way Sasai talked, and that he seemed to have less energy than before.
Sasai’s colleagues at Riken said he had been receiving mental counseling since the scandal surrounding papers on STAP, or stimulus-triggered acquisition of pluripotency, cells, which was lead-authored by Obokata, came to light earlier this year.
Kagaya added that Sasai was hospitalized for nearly a month in March due to psychological stress related to the scandal, but that he “recovered and had not been hospitalized since.”
A series of allegations surfaced over the credibility of two papers on STAP cells that were published in British science journal Nature in January but then were retracted in July.
Sasai supervised Obokata’s writing. A Riken investigative committee has said Sasai bore heavy responsibility for not confirming data for the STAP study and for Obokata’s misconduct.
Obokata is now engaged in experiments at Riken to verify the findings of the research.
Sasai’s team retracted the research papers from Nature over Obokata’s alleged malpractice, which she has contested.
Retractions of papers in major scientific journals are rare, and the scandal was a major embarrassment to Japan’s scientific research.
In two papers published earlier this year in the journal Nature, the researchers reported that they successfully transformed ordinary mouse cells into versatile stem cells by exposing them to a mildly acidic environment. Scientists hope to harness stem cells to grow replacement tissue for treating a variety of diseases.
Riken later held Obokata responsible for falsifying data. The investigation also focused on Sasai and two other employees, though the three were not accused of research misconduct.
Sasai had said he was “deeply ashamed” over the problems in the papers.