Less than 40 days after a team led by Haruko Obokata of the RIKEN Center for Developmental Biology in Kobe, Japan, presented two stunning papers claiming a method of using a simple acid-bath method to reprogramme mature mammalian cells back to an embryonic state — so called STAP cells — researchers in Japan, including one of the papers’ co-authors, are calling for them to be retracted.

Within weeks of their 30 January publication, the paper was criticized for irregularities and apparent duplicated images. Numerous scientists also had difficulty reproducing the supposedly simple method. The team responded with the promise of corrections and a list of tips to help other scientists to reproduce the results.

Over the weekend, however, two more serious problems surfaced. The Nature paper was found to contain two images apparently duplicated from Obokata’s doctoral dissertation. Her thesis also reported experiments dealing with cells that were supposedly in an embryonic state, but the cells reported in the Nature paper were said to be derived from a different process in an altogether different experiment.

The revelation has led to a flurry of calls — including some from senior scientists in Japan — for the paper to be retracted.

Perhaps the most damning comes from Teruhiko Wakayama, a cloning expert at Yamanashi University and a corresponding author on one of the papers. Interviewed by NHK news, Wakayama said: “I have lost faith in the paper. Overall there are now just too many uncertainties about it. I think we have to wait for some confirmation.” Wakayama calls for an investigation of all the laboratory notebooks and data. He continues: “To check the legitimacy of the paper, we should retract it, prepare proper data and images, and then use those to demonstrate, with confidence, that the paper is correct.” Wakayama reportedly contacted all of the authors requesting that they agree to retract the paper. RIKEN says it is still investigating the case.