title: Direct visualization of the endomitotic cell cycle in living megakaryocytes: differential patterns in low and high ploidy cells.
abstract: Endomitosis in megakaryocytes (MKs) involves repeated DNA replication in the absence of cytokinesis and is a crucial part of MK development. However, chromosomal dynamics have never been observed in living MKs. We developed a new transgenic mouse model in which the expression of human histone H2B fused in-frame to green fluorescent protein is targeted to MKs. Ex vivo time-lapse microscopy analysis indicated that chromosomal condensation occurs at early mitosis in all MKs. In high ploidy MKs (>or=8N), late anaphase was marked by a ring-type alignment of chromosomes with multiple territories formed between them. By contrast, in low ploidy MKs mitotic chromosomes segregated to form two groups separated by a clear space before re-joining to one cluster. This is the first study to document chromosomal segregation patterns during endomitosis ex vivo and to indicate their potential differential regulation in low and high ploidy cells.
authors.affiliation: Department of Biochemistry, Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, Massachusetts 02118, USA.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Papadantonakis
authors.forename: Maria
authors.initials: M
authors.lastname: Makitalo
authors.forename: Donald J
authors.initials: DJ
authors.lastname: McCrann
authors.forename: Kenian
authors.initials: K
authors.lastname: Liu
authors.forename: Hao G
authors.initials: HG
authors.lastname: Nguyen
authors.forename: Greg
authors.initials: G
authors.lastname: Martin
authors.forename: Sunita
authors.initials: S
authors.lastname: Patel-Hett
authors.forename: Joseph E
authors.initials: JE
authors.lastname: Italiano
authors.forename: Katya
authors.initials: K
authors.lastname: Ravid
mesh_terms: D000818:Animals; D002453:Cell Cycle / Q000502:physiology*; D020090:Chromosome Segregation / Q000502:physiology; D049452:Green Fluorescent Proteins / Q000235:genetics; D006657:Histones / Q000235:genetics; D008533:Megakaryocytes / Q000166:cytology* / Q000378:metabolism* / Q000502:physiology; D051379:Mice; D008822:Mice, Transgenic; D008938:Mitosis / Q000502:physiology*; D010978:Platelet Factor 4 / Q000235:genetics; D011003:Ploidies; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D006657:Histones; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D010978:Platelet Factor 4