The search for new ES cell markers is critical not only for identification, isolation and visualization of embryonic stem (ES) cells, but also for potential clinical treatment as a targeting agent. Here, by using phage display technology, 12-mer peptide ligands that bind specifically to mouse ES cells were isolated. After four rounds of negative-positive selection, nine sequences in 20 random samples from the chosen clones were selected. Enzyme-linked immunosorbent assay results suggested the Seq2 peptide (KHMHWHPPALNT) had high affinity and specificity to the mouse ES cells. The binding capability of the Seq2 phage could be matched with that of a chemically synthesized peptide with a sequence identical to that displayed by the phage, indicating that this ability was due to the peptide sequence itself. Immunofluorescence analysis confirmed that Seq2 phage selectively bound to the mouse ES cells but not to the differentiated mouse ES cells. Western blot analysis proved the Seq2 phage was bound to two mouse ES membrane proteins which were about 18/20KD, suggesting that the selected peptide targeted to a unique receptor expressed on the mouse ES cells with specificity. Peptides obtained from the study may provide a way to label, identify, and characterize ES cells.
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