Author of disputed stem cell paper found dead

A Japanese scientist who co-authored a discredited study purporting to describe a revolutionary method of creating stem cells was found dead on Tuesday, after apparently hanging himself at the laboratory complex where he worked.

Yoshiki Sasai was deputy director of the prestigious Riken Center for Developmental Biology in Kobe and the direct supervisor of the stem-cell study's disgraced lead researcher, Haruko Obokata.

Their work, published in two papers in the journal Nature in January, stunned biologists around the world with its claim that embryo-like stem cells could be created cheaply and simply by bathing adult blood cells in a mild acid solution. But the assertion was quickly challenged and by April, Riken was accusing Ms Obokata of falsifying data.

The Nature papers have since been retracted, and Mr Sasai had said in interviews that he was "ashamed" of his failure to prevent the alleged misconduct. In June, an outside review commissioned by Riken called for strict penalties against Ms Obokata, Mr Sasai and other Riken personnel and said the developmental biology centre should be disbanded.

The saga has drawn intense public attention in Japan, a reflection both of Ms Obokata's status as a high-profile young female scientist - she was just 30 when the Nature papers were published - and hopes that stem-cell medicine might become a major national industry. The cells have enormous potential in treating diseases because of their ability to grow into any sort of tissue.

Last month NHK, Japan's normally staid public broadcaster, apologised to Ms Obokata after reporters seeking an interview chased her through the streets of Kobe on a motorbike, then pursued her into a hotel toilet. She said she sustained a sprained elbow in the fracas.

Ms Obokata has stood by the claims made in the Nature papers, but neither she nor other researchers have managed to replicate the experiments that she says created stem cells using the acid-bath method, called stimulus-triggered acquisition of pluripotency, or STAP. She has generally avoided appearing in public during the controversy, but a Riken spokesman said she was "shocked" by news of Mr Sasai's death.

Ichita Yamamoto, sciences minister, also said on Tuesday he was "extremely shocked". "In the world of regenerative medicine, Mr Sasai was a researcher who represented Japan," he told reporters.

According to police reports and comments by Riken, Mr Sasai's body was discovered on Tuesday morning hanging from a rope from a staircase railing in one of the centre's buildings. Suicide notes were discovered nearby.

The Riken spokesman, Satoru Kagaya, said Mr Sasai had appeared "mentally and physically tired" in recent days. Masatoshi Takeichi, director of the Center for Developmental Biology and Mr Sasai's boss, said Mr Sasai had expressed a wish to resign in March.

"He changed his mind, probably because the investigation into the STAP controversy was still ongoing, but he felt a strong sense of responsibility," Mr Takeichi said.

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