The Asahi Shimbun via Getty Images

The investigative committee that said a RIKEN scientist had committed misconduct, presenting its findings on 1 April in Tokyo. From left to right: Shunsuke Ishii, Atsushi Iwama, Haruhiko Koseki, Yoichi Shinkai, Tetsuya Taga and Jun Watanabe

Four of the six members of a Japanese committee that found misconduct in studies claiming to demonstrate a simple technique to produce stem cells are now facing allegations of irregularities in their own published work.

The allegations complicate an already murky controversy over the technology, known as stimulus-triggered acquisition of pluripotency (STAP). Stem-cell biologist Haruko Obokata of the RIKEN Center for Developmental Biology in Kobe, Japan, described in two Nature papers published on 30 January1, 2 how she and her colleagues had reprogrammed mouse cells into stem cells by soaking them in acid or applying physical pressure.

Within weeks, numerous problems with the papers surfaced, including manipulated and duplicated images. On 1 April Obokata was charged with misconduct by a RIKEN investigative committee comprising five scientists and a lawyer. Obokata appealed the judgement on 8 April, and the committee was given 50 days to consider that appeal. On 6 May, the Japanese media reported that the investigative committee decided to deny Obokata's request for a re-examination. Obokata can no longer appeal the finding through the organization's appeal system. RIKEN will now begin the process of deciding penalties to Obokata and her co-authors.

On 25 April, the head of the investigation committee, Shunsuke Ishii, resigned from the committee after manipulated images from two of his earlier papers were posted on the Internet. Ishii maintains that neither of the problems amount to fraud, and he posted photos from the original laboratory notebooks to support that point. RIKEN launched a preliminary inquiry into his papers.

More trouble arose for RIKEN on 30 April, when a whistle-blower alleged problems in the images of papers co-authored by two other RIKEN researchers on the committee, Haruhiko Koseki and Yoichi Shinkai. RIKEN launched a preliminary investigation into the allegations that same day. Satoru Kagaya, a RIKEN spokesman, says that the whistle-blower, whose name RIKEN will not reveal, alleges that four papers from Koseki, published between 2003 and 2011, and one paper by Shinkai, published in 2005, contain data that were manipulated in one or two spots.

Meanwhile, also on 30 April, a journalist from the daily newspaper Asahi Shimbun notified Tokyo Medical and Dental University of allegations regarding Tetsuya Taga, the university's president and another one of the RIKEN panel investigators. Two papers on neural stem cells co-authored by Taga, from 2004 and 2005, each had two illustrations that, the journalist said, appeared to be manipulations.

The next day, the university launched a preliminary enquiry headed by four university administrators. After one day of deliberation, which included a discussion with Taga and two co-authors and an examination of laboratory notebooks, the university concluded that Taga was not guilty of misconduct. A university spokesperson declined to say whether the university found no manipulations at all or whether they found manipulations but deemed them not to be misconduct. The spokesperson said a clarification of that issue will be posted online tomorrow.

Obokatas lawyer has stated that the problems in the committee members' papers are akin to those found in Obokatas errors, but not fraud.

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Accusations pile up amid Japans stem-cell controversy