(Reference: a briefing narrated by H.Obokata in the international press conference held by Nature on 28th January, 2014)
Our main findings reported in STAP papers were as follows.
When ordinary somatic cells, such as lymphocytes from newborn mice, were shocked with a dose of sublethal stress, such as low pH or mechanical force, they were stripped of their differentiation memory, and reverted to a state of pluripotency that, in many ways, resembled what is seen in ES cells. We named this conversion process STAP, which stands for
and the cells resulting from this process, we called STAP cells. STAP cells showed all the hallmarks of pluripotency, and could contribute to chimeric mice and germline transmission when injected into early-stage embryos. It was really surprising to see that such a remarkable transformation could be triggered simply by stimuli from outside of the cell.
We also found the culture conditions in which STAP cells could be robustly expanded as stem cell lines. In fact, STAP cells showed an intriguing difference from ES cells and iPS cells. When injected into mouse blastocysts, both ES cells and iPS cells can differentiate into somatic cells of the fetus, but they cannot form placenta. In contrast, STAP cells could contribute to both the somatic cells and the placenta, suggesting that STAP cells might represent an even more immature state.
Two types of stem cell lines were established from STAP cells. One was called STAP stem cells which were subcultured in ES medium. The character of STAP stem cells was quite similar to both ES cells and iPS cells. When injected in to mouse blastocysts, STAP stem cells could contribute only to fetuses. Another was called FI (FGF4-Induced) stem cells. When cultured in TS (trophoblast stem) cell medium, STAP cells also obtained a strong proliferative potential. These cells took over the unique characters of STAP cells, and were able to contribute not only to fetuses but also placentas as well as STAP cells.
Role-sharing in STAP study
I, Haruko Obokata, was a first author of both of these papers. Although the idea of STAP was conceived of by Drs. Charles and Martin Vacanti, and born in Dr. Vacanti’s lab at Harvard University, where the preliminary studies were done, all practical experiments for STAP papers were performed in Dr. Wakayama’s lab at RIKEN CDB in Japan. Dr, Wakayama was my boss and mentor. I was a member of his lab for 2 years. He instructed me very closely when STAP cell research was progressing. I did all experiments for STAP papers under his supervision.
STAP research was proceeded within a division of roles. My part of STAP cell research was to create STAP cells that expressed pluripotent stem cell markers. Important pluripotency tests of STAP cells, chimeric mouse generation and STAP stem cell line establishment, were Dr. Wakayama’s part. Chimeric contribution of STAP cells to placentas was also discovered by Dr. Wakayama.
Investigation report of STAP in RIKEN
STAP (Stimulus Triggered Acquisition of Pluripotency), cell concept is one in which “mature adult cells are reprogrammed to pluripotent stem cells by external stresses” that was published as two papers in Nature at the end of January 2014. The first paper mainly reported “STAP phenomenon” showing that which mature cells were reprogrammed to pluripotent stem cells by external stresses. The second paper mainly reported the characteristics of cell lines established from STAP cells. Soon after their publication, these papers were retracted in July, 2014 because of multiple errors in the figures published in the manuscripts.
According to the final report of the STAP cell investigation at RIKEN, it was found that all chimeric mice, both of cell lines and a teratoma were derived from ES cells and not STAP cells. However, only teratoma formation from STAP like cells was already confirmed in 2010 in Dr. Vacanti’s lab at Harvard University.
STAP verification experiment in RIKEN CDB
The verification experiment of STAP was held in RIKEN CDB in 2014. The STAP verification experiment was conducted by two independent groups. One was Dr. Hitoshi Niwa’s STAP verification experiment team. The other was Obokata alone (but analyses of re-created cells were performed by other people). I joined in the STAP verification study alone, by myself, for four months.
My STAP verification experiment was performed under strict surveillance. I was required to wear clothes with no pockets, and furthermore surveillance agents tied an apron on to me every day. Even small nail holes in the wall of the experiment room were infilled. In addition to 24-hour video surveillance, I was monitored my every move and my every action was documented by surveillance agents. I could not even pick up reagent bottles freely. Also, I was not allowed to analyze re-created STAP cells on my own. Therefore, I could not even know whether my experiments went well or not. I was only allowed to perform the same task over and over every day in bad physical and mental condition.
Notwithstanding, my part of STAP study, and STAP phenomenon, was surely confirmed in the verification experiment. Indeed, Dr. Niwa’s STAP verification group also independently succeeded in re-creating STAP cells which expressed pluripotent stem cell markers such as Oct4. However, because Dr. Wakayama refused to join the verification experiment of STAP in RIKEN, his part of STAP study, the limits of STAP cell’s power, became unclear. In those chimeric mouse generation experiments, he employed a specialized technique whereby he cut STAP cell clusters into small pieces by using a micro-knife.
My PhD was forfeited by Waseda University in November 2015. I published a book in January, 2016 entitled “Anohi” (meaning ‘that day’ in English) describing the series of events regarding STAP. I opened “STAP HOPE PAGE” in March 2016 to assist future researchers investigating into the STAP phenomenon.
I am unable to further continue my own STAP research. All I can do is to leave my recipe to create STAP cells here. My fervent hope is that someone will open the next door to the secrets of life. STAP phenomenon may be the key to the door. I believe that STAP phenomenon will prove to be a great contribution to humanity in the future.