As doubts have been raised over research papers published in the scientific journal Nature about stimulus-triggered acquisition of pluripotency (STAP) cells, there is a strong possibility papers on the subject will be withdrawn, a situation that would shake confidence in Japanese scientific research.

Even if the papers are withdrawn, the possibility remains that STAP cells were actually created. However, withdrawal of the papers would not only send STAP cell research back to square one, but could also damage the credibility of Japan's scientific studies.

In January, an international research team led by RIKEN researcher Haruko Obokata announced the creation of STAP cells, which are described as a third kind of pluripotent cells, following two similar types — embryonic stem (ES) cells and induced pluripotent stem (iPS) cells.

"I think senior officials at RIKEN regard the mistakes as almost fatal," Teruhiko Wakayama, a professor at the University of Yamanashi and one of the coauthors of the papers, told reporters Tuesday morning at the university.

Wakayama said he received emails from two senior officials at RIKEN's Center for Developmental Biology (CDB) on Monday, when it was discovered that images used in the STAP cell papers looked almost identical to those used in Obokata's doctoral thesis. In the emails, they said, "Under the circumstances, there is no choice but to withdraw the papers."

Obokata also belongs to the Kobe-based CDB as the research unit leader of the Laboratory for Cellular Programming.

Furthermore, another senior official at the CDB advised Wakayama on the phone, "You should call for the withdrawal of the papers," which made him decide to do so.

Nature is a prestigious scientific journal in which researchers around the world hope to have their theses published. The selection process is highly competitive, with the acceptance rate for articles at about 8 percent.

"If a research paper is published in the journal, it gives the author an advantage in acquiring research funds, including those from the government, and enhances his or her prestige as a researcher," one researcher said.

According to Shigeaki Yamazaki, a professor at Aichi Shukutoku University who is familiar with issues concerning research fraud, an international database storing academic papers published in the last 15 years shows that about 3,000 papers in the field of life science research have been withdrawn.

In the past, a South Korean researcher published a paper in which he claimed to have created human embryonic stem cells through cloning. However, it was later discovered that the paper had been based on falsified evidence, dealing a serious blow to the ES cell research field.

In regard to the two articles on STAP cells carried in the Jan. 30 issue of Nature, problems such as the use of two identical images surfaced in mid-February. While RIKEN has not provided any detailed explanations, maintaining that "the fundamentals of the research will not be affected," many researchers have pointed out that pictures and quotations in the papers are "unnatural" or "questionable."

In response to inquiries from researchers who said they were unable to reproduce STAP cells in experiments using the method outlined in the papers, RIKEN provided details for producing STAP cells and other technical tips on its website on March 5.

However, doubts about the papers have continued to be raised, and it was discovered Tuesday that Obokata's doctoral thesis contained a large number of descriptions suspected to be quotations used without permission.

On the creation of STAP cells, "the facts have not been shaken," a RIKEN public relations official said during a press conference held at the Education, Culture, Sports, Science and Technology Ministry on Tuesday.

"But there are suspicions about the process."

The administration of Prime Minister Shinzo Abe had high expectations for STAP cells, positioning the nurturing of the medical industry as one of the pillars of its growth strategy. The government even made an immediate decision to assist STAP cell studies.

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Yomiuri Shimbun staff writer Takashi Hagihara contributed to this report.