title: Regulation of spindle orientation and neural stem cell fate in the Drosophila optic lobe.
abstract: BACKGROUND
  The choice of a stem cell to divide symmetrically or asymmetrically has profound consequences for development and disease. Unregulated symmetric division promotes tumor formation, whereas inappropriate asymmetric division affects organ morphogenesis. Despite its importance, little is known about how spindle positioning is regulated. In some tissues cell fate appears to dictate the type of cell division, whereas in other tissues it is thought that stochastic variation in spindle position dictates subsequent sibling cell fate.
  
  
  RESULTS
  Here we investigate the relationship between neural progenitor identity and spindle positioning in the Drosophila optic lobe. We use molecular markers and live imaging to show that there are two populations of progenitors in the optic lobe: symmetrically dividing neuroepithelial cells and asymmetrically dividing neuroblasts. We use genetically marked single cell clones to show that neuroepithelial cells give rise to neuroblasts. To determine if a change in spindle orientation can trigger a neuroepithelial to neuroblast transition, we force neuroepithelial cells to divide along their apical/basal axis by misexpressing Inscuteable. We find that this does not induce neuroblasts, nor does it promote premature neuronal differentiation.
  
  
  CONCLUSIONS
  We show that symmetrically dividing neuroepithelial cells give rise to asymmetrically dividing neuroblasts in the optic lobe, and that regulation of spindle orientation and division symmetry is a consequence of cell type specification, rather than a mechanism for generating cell type diversity.
authors.affiliation: The Wellcome Trust/Cancer Research UK Gurdon Institute and Department of Physiology, Development and Neuroscience, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK. b.egger@gurdon.cam.ac.uk
authors.forename: Boris
authors.initials: B
authors.lastname: Egger
authors.forename: Jason Q
authors.initials: JQ
authors.lastname: Boone
authors.forename: Naomi R
authors.initials: NR
authors.lastname: Stevens
authors.forename: Andrea H
authors.initials: AH
authors.lastname: Brand
authors.forename: Chris Q
authors.initials: CQ
authors.lastname: Doe
mesh_terms: D000818:Animals; D019521:Body Patterning / Q000502:physiology; D002455:Cell Division / Q000502:physiology*; D019070:Cell Lineage / Q000502:physiology; D016764:Cell Polarity / Q000502:physiology; D049109:Cell Proliferation; D048749:Cytokinesis / Q000502:physiology; D004331:Drosophila melanogaster / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism; D007814:Larva; D046569:Neuroepithelial Cells / Q000166:cytology; D009474:Neurons / Q000166:cytology*; D009899:Optic Lobe, Nonmammalian / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism; D038081:Organogenesis / Q000502:physiology; D008941:Spindle Apparatus / Q000502:physiology* / Q000648:ultrastructure; D013234:Stem Cells / Q000145:classification / Q000166:cytology*