Panels A to F show the MS/MS spectra of peptides from undifferentiated embryonic cell transcription factor 1 (UTF1) and DNA cytosine-5 methyltransferase 3 beta isoform 1 (DNMT3B), heat shock 27kDa protein 1 (HSPB1), CD99 antigen (CD99), podocalyxin-like isoform 1 (PODXL) and LIN28 homolog (LIN28), respectively. The reporter ions in the inset show the examples of high, low and equal expression of proteins in ESCs and ECCs.