title: Understanding the first steps in embryonic stem cell exit from the pluripotent state.
abstract: BACKGROUND
  We are interested in understanding how a given cell type, in response to external cues from its environment, makes the decision to differentiate. In the case of mouse embryonic stem cells (mESCs), the key external factor that maintains their undifferentiated state is the cytokine leukemia inhibitory factor (LIF). LIF removal causes mESCs to exit their pluripotent state and differentiate into more restricted precursors. Although LIF is known to activate multiple different phosphorylation cascades, the mechanisms by which its removal leads to mESC differentiation are not well understood.
  
  
  METHODS
  In order to identify the molecular events that occur upon LIF removal, we developed a set of novel experimental approaches that allowed identification and quantification of global phosphorylation changes that occur when mESCs are deprived of LIF. These included growth of mESCs on permeable membranes and development of a robust and sensitive phospho-proteomics platform to quantify early signaling events.
  
  
  RESULTS
  In addition to the well-characterized tyrosine 705 phosphorylation of STAT3, LIF removal results in the rapid phosphorylation of multiple other proteins known to regulate the mESC self-renewal on both tyrosine, serine, and threonine residues. We hypothesize that these unique posttranslational modifications help drive the exit of mESCs from the pluripotent state.
  
  
  CONCLUSIONS
  Our data set the stage for future studies investigating the functional role of these phosphorylation events in mESCs. These studies were greatly facilitated by the National Blood Foundation, whose support in the crucial initiation phase of these studies was invaluable.
authors.affiliation: Department of Pathology, Brigham and Women's Hospital, Joint Program in Transfusion Medicine, Department of Cancer Biology, Dana-Farber Cancer Institute, and Harvard Medical School, Boston, Massachusetts 02115, USA. cluckey@partners.org
authors.forename: C John
authors.initials: CJ
authors.lastname: Luckey
authors.forename: Yu
authors.initials: Y
authors.lastname: Lu
authors.forename: Jarrod A
authors.initials: JA
authors.lastname: Marto
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000502:physiology; D002460:Cell Line; D002678:Chimera; D019976:Cloning, Organism; D018920:Coculture Techniques / Q000295:instrumentation; D053595:Embryonic Stem Cells / Q000166:cytology*; D053605:Leukemia Inhibitory Factor / Q000037:antagonists & inhibitors / Q000502:physiology*; D051379:Mice; D010766:Phosphorylation; D039904:Pluripotent Stem Cells / Q000166:cytology*; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D040901:Proteomics; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D053605:Leukemia Inhibitory Factor; C507838:Lif protein, mouse; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases
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