title: Overexpression of cyclin D1 moderately increases ploidy in megakaryocytes.
abstract: OBJECTIVE
  Megakaryocytes undergo a unique cell cycle by which they replicate their complete genome many times in the absence of cytokinesis. In the search for regulators of the endomitotic cell cycle, we previously produced mice transgenic for cyclin D3 to identify this cyclin as able to enhance ploidy and to increase the number of differentiated cells in the megakaryocytic lineage. Of the D-type cyclins, cyclin D3 and to a much lesser extent cyclin D1, are present in megakaryocytes undergoing endomitosis and these cyclins are, respectively, markedly and moderately upregulated following exposure to the ploidy-promoting factor, Mpl-ligand. Our objective was to explore whether cyclin D1 can mimic the effect of cyclin D3 on ploidy in megakaryocytes.
  
  
  METHODS
  We generated transgenic mice overexpressing cyclin D1 in megakaryocytes and analyzed megakaryocyte ploidy, number and platelet levels in these mice and control mice.
  
  
  RESULTS
  We show that transgenic mice in which cyclin D1 is overexpressed in megakaryocytes display higher ploidy level than the control mice, with no change in the number of differentiated cells of the megakaryocytic series, or in platelet level.
  
  
  CONCLUSIONS
  Our models support a key role for D-type cyclins in the endomitotic cell cycle, and also indicate that although cyclin D3, from among the D cyclins, is unique in its high levels of expression in megakaryocytes, it is not unique in its ability to promote polyploidization.
authors.affiliation: Department of Biochemistry, Boston University School of Medicine, Boston, MA 02118, USA.
authors.forename: S
authors.initials: S
authors.lastname: Sun
authors.forename: J M
authors.initials: JM
authors.lastname: Zimmet
authors.forename: P
authors.initials: P
authors.lastname: Toselli
authors.forename: A
authors.initials: A
authors.lastname: Thompson
authors.forename: C W
authors.initials: CW
authors.lastname: Jackson
authors.forename: K
authors.initials: K
authors.lastname: Ravid
mesh_terms: D000818:Animals; D002452:Cell Count; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D015870:Gene Expression; D008533:Megakaryocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D010976:Platelet Count; D011003:Ploidies
chemical_list: D019938:Cyclin D1