Since the cell aggregates consist of ~10 cells, such expression level indicated possible existence of the cell(s) expressing pluripotency-associated genes at the equivalent level to that in ES cells.
In the present study, we investigated the properties of cell aggregates obtained by culture of liver cells transiently treated with low-pH stimulus, which was performed by the group directed by the author. We initially followed the protocol described in the original paper[1] with the detail description in protocol exchange where HCl was applied to achieve low-pH condition. However, we merely obtained the cell aggregates expressing the pluripotency makers as described in this report even when it was combined with the culture in medium containing Fgf2, which was not described in the original protocol but subsequently suggested by the authors. However, when we used ATP instead of HCl, also based on a suggestion by the authors, a few cells in a subset of cell aggregates expressed the pluripotency marker Oct3/4 at levels comparable to those in ES cells that were reproducibly detected by QPCR (Fig. 3c) and immunostaining (Fig. 4b). However, the frequency was very low; 5 × 10<to the power of 5> liver cells yielded only ~30 cell aggregates, in which about 20% of the cell aggregates contained 1–2 Oct3/4 positive cells, indicating a frequency per seeded liver cell of 0.0012–0.0024%. Moreover, the pluripotency of such cells was not confirmed by chimera formation assay, and they did not give rise to any stem cell lines. We thus conclude that such cell aggregates do not fulfill the definition for STAP cells proposed in the original studies.
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Since the cell aggregates consist of ~10 cells, such expression level indicated possible existence of the cell(s) expressing pluripotency-associated genes at the equivalent level to that in ES cells.
(英文)
We next performed qPCR on individual cell aggregates isolated from culture. Aggregates were selected and RNA samples were prepared separately. These RNAs were reverse-transcribed and qPCR was performed. We found that some aggregates expressed a comparable amount—more than 10% of the expression level in ES cells—of pluripotency-associated genes, including Oct3/4. Since the cell aggregates consist of ~10 cells, such expression level indicated possible existence of the cell(s) expressing pluripotency-associated genes at the equivalent level to that in ES cells. Klf4 expression was detected in all samples, which may reflect its expression in liver cells, and thus serves as a positive control in this assay. Of cell aggregates derived from liver cells treated with ATP, 19% expressed the amount of Oct3/4 comparable to ES cells (Fig. 3c). These data suggest that some proportion of cells in the aggregates express pluripotency-associated genes at comparable levels to those of ES cells.
