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Megakaryocytes assemble podosomes that degrade matrix and protrude through basement membrane

Hannah Schachtner, Simon D.J. Calaminus, Amy Sinclair, James Monypenny, Michael P. Blundell, Catherine Leon, Tessa L. Holyoake, Adrian J. Thrasher, Alison M. Michie, Milica Vukovic, Christian Gachet, Gareth E. Jones, Steven G. Thomas, Steve P. Watson and Laura M. Machesky

Key points

  • Murine and human megakaryocytes assemble podosomes

  • Megakaryocyte podosomes remodel matrix

Abstract

Megakaryocytes give rise to platelets via extension of proplatelet arms, which are released through the vascular sinusoids into the bloodstream. Megakaryocytes and their precursors undergo varying interactions with the extracellular environment in the bone marrow during their maturation and positioning in the vascular niche. We demonstrate that podosomes are abundant in primary murine megakaryocytes adherent on multiple extracellular matrix substrates, including native basement membrane. Megakaryocyte podosome lifetime and density, but not podosome size are dependent on the type of matrix, with podosome lifetime dramatically increased on collagen fibres compared with fibrinogen. Podosome stability and dynamics depend on actin cytoskeletal dynamics but not matrix metalloproteases. However, podosomes degrade matrix and appear to be important for megakaryocytes to extend protrusions across a native basement membrane. We thus demonstrate for the first time a fundamental requirement for podosomes in megakaryocyte process extension across a basement membrane and our results suggest that podosomes may have a role in proplatelet arm extension or penetration of basement membrane.

  • Submitted July 25, 2012.
  • Accepted December 21, 2012.