title: Phospholipase D is a central regulator of collagen I-induced cytoskeletal rearrangement and podosome formation in megakaryocytes.
abstract: BACKGROUND
  Blood platelets are small anucleated cell fragments generated from bone marrow megakaryocytes (MKs) by a cytoskeleton-driven process. Thereby, mature MKs form long cytoplasmic protrusions (pro-platelets), which extend into the sinusoids within the bone marrow and finally release platelets. Podosomes are F-actin rich matrix contacts that have been suggested to play an important role in cell migration, but also in pro-platelet formation by MKs. Phospholipase D (PLD) has been proposed to contribute to the regulation of actin dynamics through the local generation of phosphatidic acid but its role in platelet formation is unknown.
  
  
  OBJECTIVE
  We sought to investigate the significance of PLD in MK podosome formation and thrombocytopoiesis.
  
  
  METHODS
  Podosome formation, spreading and ultra-structure of PLD single- and double-deficient MKs were analyzed using confocal and transmission electron microscopy.
  
  
  RESULTS
  Phospholipase D-deficient MKs displayed a highly altered ultra-structure in vivo and abnormal actin rearrangement, with almost abolished formation of podosomes upon spreading on collagen I in vitro. However, MK endomitosis and platelet production were not altered by PLD deficiency.
  
  
  CONCLUSIONS
  Together, our findings point to a specific function of PLD in actin dynamics as well as podosome formation and size determination in MKs on a collagen I matrix. The normal platelet number in PLD-deficient mice, however, suggests the existence of compensatory mechanisms in vivo that overcome the defective podosome formation observed in vitro.
authors.affiliation: Department of Experimental Biomedicine, University Hospital and Rudolf Virchow Center, University of Würzburg, Würzburg, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Stritt
authors.forename: I
authors.initials: I
authors.lastname: Thielmann
authors.forename: S
authors.initials: S
authors.lastname: Dütting
authors.forename: D
authors.initials: D
authors.lastname: Stegner
authors.forename: B
authors.initials: B
authors.lastname: Nieswandt
mesh_terms: D000818:Animals; D024042:Collagen Type I / Q000502:physiology*; D003599:Cytoskeleton / Q000378:metabolism*; D008533:Megakaryocytes / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D046529:Microscopy, Electron, Transmission; D010739:Phospholipase D / Q000235:genetics / Q000378:metabolism*
chemical_list: D024042:Collagen Type I; D010739:Phospholipase D
keywords: actins; collagen; cytoskeleton; megakaryocytes; phospholipase D