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Updated: Jul 3, 2026
In Situ Exploration of Murine Megakaryopoiesis using Transmission Electron Microscopy
Published on: September 8, 2021
Direct visualization of the endomitotic cell cycle in living megakaryocytes: differential patterns in low and high
Nicholas Papadantonakis1, Maria Makitalo, Donald J McCrann
1Department of Biochemistry, Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, Massachusetts 02118, USA.
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.
Insights
This study visualizes chromosomal dynamics during megakaryocyte endomitosis using a novel mouse model. It reveals distinct chromosome segregation patterns in high versus low ploidy cells, offering new insights into cell development.
Area of Science:
- Cell Biology
- Developmental Biology
- Genetics
Background:
- Endomitosis is essential for megakaryocyte (MK) development, involving DNA replication without cell division.
- Chromosomal dynamics during MK endomitosis have not been previously visualized in live cells.
Purpose of the Study:
- To develop a method for observing chromosomal dynamics in living MKs during endomitosis.
- To characterize and compare chromosome segregation patterns in MKs of varying ploidy levels.
Main Methods:
- Developed a transgenic mouse model expressing histone H2B-GFP in MKs.
- Utilized ex vivo time-lapse microscopy to observe mitosis in MKs.
Main Results:
- Observed chromosomal condensation in all MKs during early mitosis.
- Documented unique ring-type chromosome alignment and territory formation in high ploidy MKs (>or=8N) during late anaphase.
- Identified distinct segregation patterns in low ploidy MKs, with chromosomes forming two groups before re-joining.
Conclusions:
- This is the first study to visualize chromosomal segregation patterns during endomitosis in live MKs.
- Demonstrated differential regulation of chromosome segregation based on ploidy level in MKs.
