A leading Japanese research institute has opened an investigation into a groundbreaking stem cell study after concerns were raised about its credibility. 

The RIKEN centre in Kobe announced on Friday that it is looking into alleged irregularities in the work of biologist Haruko Obokata, who works at the institution. She shot to fame last month as the lead author on two papers^{1, 2} published in Nature that demonstrated a simple way to reprogram mature mice cells into an embryonic state by simply applying stress, such as exposure to acid or physical pressure on cell membranes. The RIKEN investigation follows allegations on blog sites about the use of duplicated images in Obokata’s papers, and numerous failed attempts to replicate her results.    

Cells in an embryonic state can turn into the various types of cells that make up the body, and are therefore an ideal source of patient-specific cells. They can be used to study the development of disease or the effectiveness of drugs and could also be transplanted to regenerate failing organs. A consistent and straightforward path to reprogramming mature cells was first demonstrated in 2006, when a study showed that the introduction of four genes could switch the cells into an embryonic form known as induced pluripotent stem (iPS) cells³. The introduction of genes, however, introduces uncertainties about the fidelity of the cells, and Obokata’s reports that the feat could be done so simply were met with awe, and a degree of scepticism (see 'Acid bath offers easy path to stem cells').

That scepticism deepened last week when blogs such as PubPeer started noting what seem to be problems in the two Nature papers and in an earlier paper from 2011⁴, which relates to the potential of stem cells in adult tissues. In the 2011 paper, on which Obokata is first author, a figure showing bars meant to prove the presence of a certain stem-cell marker appears to have been inverted and then used to show the presence of a different stem-cell marker. A part of that same image appears in a different figure indicating yet another stem-cell marker. The paper contains another apparent unrelated duplication.

The corresponding author of that study, Charles Vacanti, an anaesthesiologist at Harvard Medical School in Boston, told Nature that he learned only last week of a “mix up of some panels”. He has already contacted the journal to request a correction. “It certainly appears to have been an honest mistake [that] did not affect any of the data, the conclusions or any other component of the paper,” says Vacanti.

The problems in the two recent Nature papers, on both of which Obokata is a corresponding author (Vacanti is a co-author on both, and corresponding author on one), also relate to images. In one paper¹, one of the sections in a genomic analysis in the first figure appears to be spliced in. In the other paper², images of two placentas meant to be from different experiments look strikingly similar.

Teruhiko Wakayama, a cloning specialist at Yamanashi University in Yamanashi prefecture, is a co-author on both of the papers and took most of the placental images. He admits that the two look similar but says it may be a case of simple confusion. Wakayama, who left RIKEN during the preparation of the manuscript, says he sent more than a hundred images to Obokata and suggests that there was confusion over which to use. He says he is now looking into the problem.

The skepticism has been inflamed by reports of difficulty in reproducing Obakata’s latest results. None of ten prominent stem cell scientists who responded to a questionnaire from Nature has had success. A blog soliciting reports from scientists in the field reports eight failures. But most of those attempts did not use the same types of cells that Obokata used.

Some researchers do not see a problem yet. Qi Zhou, a cloning expert at the Institute of Zoology in Beijing, who says most of his mouse cells died after treatment with acid, says that “setting up the system is tricky”. “As an easy experiment in an experienced lab can be extremely difficult to others, I won’t comment on the authenticity of the work only based on the reproducibility of the technique in my lab,” says Zhou.

Jacob Hanna, a stem cell biologist at the Weizmann Institute of Science in Rehovot, Israel, however, says “we should all be cautious not to persecute novel findings” but that he is “extremely concerned and sceptical”. He plans to try for about two months before giving up.

The protocol might just be complicated — even Wakayama has been having trouble reproducing the results. He and a student in his laboratory did replicate the experiment independently before publication, after being well coached by Obokata. But since he moved to Yamanashi, he has had no luck. “It looks like an easy technique — just add acid — but it’s not that easy,” he says.

Wakayama says that his independent success in reproducing Obokata’s results is enough to convince him that the technique works. He also notes that the cells produced by Obokata are the only ones known — aside from those in newly fertilized embryos — to be able to produce, for example, placenta, so could not have been substituted cells. “I did it and found it myself,” he says. “I know the results are absolutely true.”

Several scientists have contacted one or some of the authors for more details on the protocol without getting a response. Hongkui Deng, a stem cell biologist at Peking University in Beijing, was told that “the authors will publish a detailed protocol soon”. Vacanti says he has had no problem repeating the experiment and says he will let Obokata supply the protocol “to avoid any potential for variation that could lead to confusion”.

Obokata did not respond to enquiries from Nature's news team.

A spokesperson for Nature Publishing Group, which publishes Nature, said: “The matter has been brought to Nature’s attention and we are investigating.”