Nobel Prize winner Shinya Yamanaka today joined a growing crowd of Japanese stem cell scientists who have held press conferences in recent weeks to apologize for mistakes in published papers. Yamanaka discovered in 2006 a way to reprogram adult cells into embryolike ones, called induced pluripotent stem (iPS) cells, a find that has revolutionized the stem cell field. He was honored in 2012 with the Nobel Prize in physiology or medicine and is one of Japan’s most famous researchers. The iPS cell research is not in question, but a frenzy of anonymous bloggers searching for flaws in prominent researchers’ papers did find fault with one of his older publications.

At a press conference today, he said that a paper published in 2000 contains an image that may be incorrect. Anonymous online posts first raised questions about the image, and Kyoto University has investigated the paper at Yamanaka’s request, The Wall Street Journal reports. The university found no problems with the paper’s conclusions, but Yamanaka says he no longer has the records needed to verify the image, because the experiment was done by collaborators. He said he will take it as a lesson on the importance of taking and preserving "proper notes that can be presented at any time."

Apparently fighting back tears (video in Japanese), Yamanaka told the press conference, "Under recent circumstances, when confidence in the trustworthiness of Japan's research has been shaken, this kind of announcement must be made. I apologize from the bottom of my heart."  He then stood and made a ritual bow of apology.

Yamanaka was referring to a recent string of public apologies by stem cell scientists in Japan, triggered by two high-profile papers published earlier this year that claim to have found an alternate way to reprogram adult cells into embryolike ones—called STAP (stimulus-triggered acquisition of pluripotency) cells. Other labs have not been able to replicate that work, and an investigating committee found evidence of misconduct by lead author Haruko Obokata. The leaders of the RIKEN institute where Obokata works, several of Obokata’s co-authors, and Obokata herself have all publicly apologized for the mistakes and the confusion they have caused. Last week, the saga took a new twist when the chair of the investigating committee, Shunsuke Ishii, resigned after evidence surfaced of problems in publications he had co-authored. (An investigation is ongoing.) He apologized as well.

Yamanaka was not involved in the STAP cell research. His reprogramming methods were quickly replicated by other scientists and are now widely used around the world.

With reporting by Dennis Normile.