| Summary: | BACKGROUND: Recent studies have shown that embryonic stem (ES) cells globally express most genes in the genome at the mRNA level; however, it is unclear whether this global expression is propagated to the protein level. Cell surface proteins could perform critical functions in ES cells, so determining whether ES cells globally express cell surface proteins would have significant implications for ES cell biology. METHODS AND PRINCIPAL FINDINGS: The surface proteins of mouse ES cells were purified by biotin labeling and subjected to proteomics analysis. About 1000 transmembrane or secreted cell surface proteins were identified. These proteins covered a large variety if functional categories including signal transduction, adhesion and transporting. More over, mES cells promiscuously expressed a wide variety of tissue specific surface proteins. And many surface proteins were expressed heterogeneously on mES cells. We also find that human ES cells express a wide variety of tissue specific surface proteins. CONCLUSIONS/SIGNIFICANCE: Our results indicate that global gene expression is not simply a result of leaky gene expression, which could be attributed to the loose chromatin structure of ES cells; it is also propagated to the functional level. ES cells may use diverse surface proteins to receive signals from the diverse extracellular stimuli that initiate differentiation. Moreover, the promiscuous expression of tissue specific surface proteins illuminate new insights into the strategies of cell surface marker screening.
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