Fig. 3

Semiquantitative comparison of Raman images by cluster analysis. KCA performed on the PCA results for Raman assignment of different cellular regions. Top row reports results for three typical hESCs, while second row reports results for three typical hiPSCs (scale bar = 5 μm). For the KCA calculation, six clusters were imposed within the cells (see text for further details), and the red cluster is only evident in hiPSCs (upper panel). Lower graph shows average Raman spectra of each cluster, where the curves have the same color as the corresponding cluster. The red curve exhibits all of the major peaks ascribed to DNA/RNA bases, and consequently the red regions inside the cells are assigned to DNA/RNA compartments. The absence of red clusters inside hESCs does not mean that DNA/RNA bases are missing therein, only that their expression is much lower than the DNA/RNA abundance in the red regions of hiPSCs