On 2016 Jul 21, Jacob H. Hanna commented:

In 2014, Theunissen et al. Cell Stem Cell 2014 Theunissen TW, 2014 reported absolute failure to detect human naïve PSC derived cell integration in chimeric mouse embryos obtained following micro-injection into mouse blastocysts, as was reported for the first time by our group (Gafni et al. Nature 2013). However, the authors failed to discuss that imaging and cell detection methods applied by Theunissen et al. Cell Stem Cell 2014 were (and still) not at par with those applied by Gafni et al. Nature 2013.

Regardless, we find it important to alert the readers that Theunissen and Jaenisch have now revised (de facto, retracted) their previous negative results, and are able to detect naïve human PSC derived cells in mouse embryos at more than 0.5-2% of embryos obtained (Theunissen et al. Cell Stem Cell 2016 - Figure 7) Theunissen TW, 2016 < http://www.cell.com/cell-stem-cell/fulltext/S1934-5909(16)30161-8 >. They now apply GFP and RFP flourescence detection and PCR based assays for Mitochondrial DNA, which were applied by the same group to elegantly claim contribution of human neural crest cells into mouse embryos (albeit also at low efficiency (Cohen et al. PNAS 2016 Cohen MA, 2016).

While the authors of the latter recent paper avoided conducting advanced imaging and/or histology sectioning on such obtained embryos, we also note that the 0.5-2% reported efficiency is remarkable considering that the 5i/LA (or 4i/LA) naïve human cells used lack epigenetic imprinting (due to aberrant near-complete loss of DNMT1 protein that is not seen in mouse naive ESCs!! http://imgur.com/M6FeaTs ) and are chromosomally abnormal. The latter features are well known inhibitors for chimera formation even when attempting to conduct same species chimera assay with mouse naïve PSCs.

Jacob (Yaqub) Hanna M.D. Ph.D.

Department of Molecular Genetics (Mayer Bldg. Rm.005)

Weizmann Institute of Science | 234 Herzl St, Rehovot 7610001, Israel

Email: jacob.hanna at weizmann.ac.il

Lab website: http://hannalabweb.weizmann.ac.il/

Twitter: @Jacob_Hanna

On 2016 Jul 21, Jacob H. Hanna commented:

In 2014, Theunissen et al. Cell Stem Cell 2014 Theunissen TW, 2014 reported absolute failure to detect human naïve PSC derived cell integration in chimeric mouse embryos obtained following micro-injection into mouse blastocysts, as was reported for the first time by our group (Gafni et al. Nature 2013). However, the authors failed to discuss that imaging and cell detection methods applied by Theunissen et al. Cell Stem Cell 2014 were (and still) not at par with those applied by Gafni et al. Nature 2013.

Regardless, we find it important to alert the readers that Theunissen and Jaenisch have now revised (de facto, retracted) their previous negative results, and are able to detect naïve human PSC derived cells in mouse embryos at more than 0.5-2% of embryos obtained (Theunissen et al. Cell Stem Cell 2016 - Figure 7) Theunissen TW, 2016 < http://www.cell.com/cell-stem-cell/fulltext/S1934-5909(16)30161-8 >. They now apply GFP and RFP flourescence detection and PCR based assays for Mitochondrial DNA, which were applied by the same group to elegantly claim contribution of human neural crest cells into mouse embryos (albeit also at low efficiency (Cohen et al. PNAS 2016 Cohen MA, 2016).

While the authors of the latter recent paper avoided conducting advanced imaging and/or histology sectioning on such obtained embryos, we also note that the 0.5-2% reported efficiency is remarkable considering that the 5i/LA (or 4i/LA) naïve human cells used lack epigenetic imprinting (due to aberrant near-complete loss of DNMT1 protein that is not seen in mouse naive ESCs!! http://imgur.com/M6FeaTs ) and are chromosomally abnormal. The latter features are well known inhibitors for chimera formation even when attempting to conduct same species chimera assay with mouse naïve PSCs.

Jacob (Yaqub) Hanna M.D. Ph.D.

Department of Molecular Genetics (Mayer Bldg. Rm.005)

Weizmann Institute of Science | 234 Herzl St, Rehovot 7610001, Israel

Email: jacob.hanna at weizmann.ac.il

Lab website: http://hannalabweb.weizmann.ac.il/

Twitter: @Jacob_Hanna