title: The different shades of mammalian pluripotent stem cells.
abstract: BACKGROUND
  Pluripotent stem cells have been derived from a variety of sources such as from the inner cell mass of preimplantation embryos, from primordial germ cells, from teratocarcinomas and from male germ cells. The recent development of induced pluripotent stem cells demonstrates that somatic cells can be reprogrammed to a pluripotent state in vitro.
  
  
  METHODS
  This review summarizes our current understanding of the origins of mouse and human pluripotent cells. We pay specific attention to transcriptional and epigenetic regulation in pluripotent cells and germ cells. Furthermore, we discuss developmental aspects in the germline that seem to be of importance for the transition of germ cells towards pluripotency. This review is based on literature from the Pubmed database, using Boolean search statements with relevant keywords on the subject.
  
  
  RESULTS
  There are distinct molecular mechanisms involved in the generation and maintenance of the various pluripotent cell types. Furthermore, there are important similarities and differences between the different categories of pluripotent cells in terms of phenotype and epigenetic modifications. Pluripotent cell lines from various origins differ in growth characteristics, developmental potential, transcriptional activity and epigenetic regulation. Upon derivation, pluripotent stem cells generally acquire new properties, but they often also retain a 'footprint' of their tissue of origin.
  
  
  CONCLUSIONS
  In order to further our knowledge of the mechanisms underlying self-renewal and pluripotency, a thorough comparison between different pluripotent stem cell types is required. This will progress the use of stem cells in basic biology, drug discovery and future clinical applications.
authors: Department of Reproductive Medicine and Gynaecology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors: Ewart W
authors: EW
authors: Kuijk
authors: Susana M
authors: SM
authors: Chuva de Sousa Lopes
authors: Niels
authors: N
authors: Geijsen
authors: Nick
authors: N
authors: Macklon
authors: Bernard A J
authors: BA
authors: Roelen
mesh_terms: D000818:Animals; D053624:Blastocyst Inner Cell Mass / Q000166:cytology; D002454:Cell Differentiation; D002460:Cell Line; D019070:Cell Lineage; D042002:Chromatin Assembly and Disassembly; D047108:Embryonic Development; D053595:Embryonic Stem Cells / Q000166:cytology; D044127:Epigenesis, Genetic; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D008297:Male; D051379:Mice; D010641:Phenotype; D039904:Pluripotent Stem Cells / Q000166:cytology / Q000502:physiology*; D051381:Rats