title: The beauty of asymmetry: asymmetric divisions and self-renewal in the haematopoietic system.
abstract: OBJECTIVE
  The hallmark of stem cells is their dual abilities to self-renew and to differentiate into multiple lineages. To fulfill these functions they must undergo asymmetric division. A central question in developmental biology is how can a single cell divide to produce two progeny cells that adopt different fates? We provided evidence of the significance of asymmetric division in human haematopoietic stem cells.
  
  
  RESULTS
  By monitoring the symmetry of divisions of haematopoietic stem cells and following their subsequent developmental potentials at the single cell level, we established a relationship between divisional kinetics and self-renewal capacity. Direct cell-cell contact with cellular determinants in the niche has been shown to play an essential role in maintaining stemness. The creation of in-vitro models for the niche, such as human mesenchymal stromal cells, has provided a controlled laboratory environment in which the relative significance of chemokines and adhesion molecules can be studied.
  
  
  CONCLUSIONS
  Identification of the molecular interactions between stem cells and their niche has led to an understanding of the mechanisms that control the self-renewal of stem cells. Ultimately, molecular signals triggered by adhesion and junction complexes are responsible for the adoption of specific cell fate.
authors.affiliation: Department of Medicine V, University of Heidelberg, Heidelberg, Germany. Anthony_dick.ho@urz.uni-heidelberg.de
authors.forename: Anthony D
authors.initials: AD
authors.lastname: Ho
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Wagner
mesh_terms: D000818:Animals; D002450:Cell Communication; D002455:Cell Division / Q000502:physiology*; D006412:Hematopoietic Stem Cells / Q000166:cytology*; D006801:Humans; D016023:Integrins
chemical_list: D016023:Integrins