title: c-Myc is essential for hematopoietic stem cell differentiation and regulates Lin(-)Sca-1(+)c-Kit(-) cell generation through p21.
abstract: OBJECTIVE
  The c-Myc protein is a member of the basic region/helix-loop-helix/leucine zipper (bHLHZip) transcription factor family, which is implicated in regulation of proliferation, differentiation, and apoptosis in multiple cell types. The aim of this study was to characterize the role of the proto-oncogene c-myc in hematopoietic stem cells (HSC) during postnatal development.
  
  
  METHODS
  We have generated a conditional mouse model that allows us to inactivate c-myc in bone marrow (BM) in an inducible fashion.
  
  
  RESULTS
  We show that conditional inactivation of c-Myc in BM severely impairs HSC differentiation, leading to a striking decrease in the number of lymphoid and myeloid cells. c-Myc deletion in BM causes substantial accumulation of a Lin(-)Sca-1(+)c-Kit(-) cell population expressing high levels of the cell-cycle inhibitor p21, whose origin and function are otherwise poorly characterized. In vivo inactivation of p21 and c-Myc normalizes Lin(-)Sca-1(+)c-Kit(-) cell numbers and restores normal proliferation. The potential origin and function of these cells are discussed.
  
  
  CONCLUSIONS
  c-Myc plays a role in HSC maintenance and differentiation and might be regulating generation of Lin(-)Sca-1(+)c-Kit(-) through the cell-cycle regulator p21.
authors.affiliation: Department of Immunology and Oncology, Centro Nacional de Biotecnología/CSIC, Universidad Autónoma de Madrid, Madrid, Spain.
authors.forename: Esther
authors.initials: E
authors.lastname: Baena
authors.forename: Maitane
authors.initials: M
authors.lastname: Ortiz
authors.forename: Carlos
authors.initials: C
authors.lastname: Martínez-A
authors.forename: Ignacio Moreno
authors.initials: IM
authors.lastname: de Alborán
mesh_terms: D000818:Animals; D000943:Antigens, Differentiation / Q000096:biosynthesis*; D017209:Apoptosis; D002454:Cell Differentiation / Q000502:physiology*; D049109:Cell Proliferation; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism*; D017353:Gene Deletion; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000187:drug effects; D006801:Humans; D008214:Lymphocytes / Q000166:cytology; D051379:Mice; D023421:Models, Animal; D022423:Myeloid Cells / Q000166:cytology; D000090063:Proto-Oncogene Mas; D019009:Proto-Oncogene Proteins c-kit / Q000032:analysis; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000502:physiology*
chemical_list: D000943:Antigens, Differentiation; D050759:Cyclin-Dependent Kinase Inhibitor p21; C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D016271:Proto-Oncogene Proteins c-myc; D019009:Proto-Oncogene Proteins c-kit