Yoshiki Sasai, co-author of the high-profile research that had
seemed to offer hope for replacing damaged cells or even growing new
human organs, was found early on Tuesday at the Riken institute
where he worked in Kobe, western Japan, police and the institute
"It is confirmed as a suicide," said a police spokesman. "It was a
Sasai, 52, had been hospitalized in March for stress and become less
receptive to media inquiries during the controversy over the team's
research, said Riken spokesman Satoru Kagaya.
The scientist "had seemed completely exhausted" in their last phone
conversation around May or June, Kagaya told a televised news
As deputy director of Riken's Center for Developmental Biology,
Sasai supervised the work of lead author Haruko Obokata, which took
the world of molecular biology by storm when it was published in the
British journal Nature in January.
It was retracted after months of controversy that made front-page
news in Japan and tarnished the country's reputation for scientific
"It is very unfortunate that this happened," said the government's
top spokesman, Chief Cabinet Secretary Yoshihide Suga. "Mr Sasai
contributed greatly in the field of developmental biology and was an
internationally renowned researcher."
Riken president Ryoji Noyori expressed "deep regret over the loss of
an irreplaceable scientist."
In what looked like game-changing discovery, Obokata, Sasai and the
other authors described simple ways to reprogram mature animal cells
back to an embryonic-like state, allowing them to generate many
different types of cells.
But questions soon arose about the research, as other scientists
could not replicate the startling claims. Riken said its
investigation found Obokata had plagiarized and fabricated parts of
the papers, raising doubts about the credibility of Japanese
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After defending her work for months against Riken's claims, Obokata
agreed in June to retract the papers, which Nature did in early
Despite the retractions of the research papers, Sasai never wavered
in his belief that Stimulus-Triggered Acquisition of Pluripotency,
or STAP, cells could exist, Japanese media said.
Obokata was "very shocked" at Sasai's suicide and was being assisted
by two Riken staffers, Kagaya said.
Sasai left five suicide notes, including two addressed to senior
Riken officials, he said. He would not disclose the contents or to
whom the other letters were addressed.
Sasai started receiving counseling in April and recently had trouble
communicating due to side-effects of medical treatments he was
undergoing, media reported.
(Reporting by Megumi Lim; Additional reporting by Kaori Kaneko;
Editing by William Mallard and Robert Birsel)
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