I have been corresponding now and then with Dr. Teru Wakayama about the ongoing STAP situation. He asked me to pass along the following message from him for clarification on the STAP Nature paper retraction and the origin of the STAP stem cells (STAP-SC).
I would like to take this opportunity to explain the reason for certain differences between the retraction statement in the published paper version of Nature Magazine and the online version of the STAP paper retraction, specifically related to reason No. (5) which was slightly different between the two.
Last month, I reported to the media about the apparent strain difference between mice used in our lab and the STAP cells. Our mouse line uniformly carries identical cag-gfp insertions in chromosome 18, however, STAP-SC appeared to have a different GFP insertion site in chromosome 15. After learning this, I asked for a further analysis to obtain more hints as to the original mouse strain corresponding to STAP-SC. My collaborator found that perhaps the GFP insertion site of STAP-SC was in fact not chromosome 15. However, importantly, the GFP insertion site is absolutely different between our mouse line and STAP-SC. We know this to be the case because we demonstrated that one primer (part of chromosome 18 and cag) only gave a PCR band in our mouse line, but not in the STAP-SC. Thus, the retraction reason of no. (5) is absolutely right. Meanwhile, we are now trying to find the true insertion site of GFP in STAP-SC. Unfortunately, for the paper version of Nature, I could not clarify this point because the deadline had passed. Only the online version could be corrected.
We apologize for any confusion, but in the best interests of science and complete transparency, we wish all of this information to be freely available.
Notes from Paul: I did some minor editing of this text for clarity.
Below is the online retraction statement reason no. (5):
“(5) In the Article, one group of STAP stem cells (STAP-SCs) was reported as being derived from STAP cells induced from spleens of F1 hybrids from the cross of mouse lines carrying identical cag-gfp insertions in chromosome 18 in the background of 129/Sv and B6, respectively, and that they were maintained in the Wakayama laboratory. However, further analysis of the eight STAP-SC lines indicates that, while sharing the same 129×B6 F1 genetic background, they have a different GFP insertion site. Furthermore, while the mice used for STAP cell induction are homozygous for the GFP transgene, the STAP-SCs are heterozygous. The GFP transgene insertion site matches that of the mice and ES cells kept in the Wakayama laboratory. Thus, there are inexplicable discrepancies in genetic background and transgene insertion sites between the donor mice and the reported STAP-SCs.”