Endomitosen

Endomitosen, also called endomitosis, is a mode of cell cycle progression in which DNA replication occurs without complete cell division, resulting in polyploid cells with enlarged nuclei. In endomitosis, the cell may enter mitosis and chromosomes condense, but cytokinesis fails or proceeds incompletely, so multiple genome copies accumulate within a single nucleus or a cell that does not fully divide. This distinguishes endomitosis from endoreduplication, where DNA replication occurs without any mitotic events.

Occurrence and examples include a variety of tissues and organisms. In mammals, megakaryocytes—the precursor cells of platelets in the bone marrow—undergo endomitosis to become polyploid, a state that supports increased cytoplasmic volume and platelet production. Some placental trophoblasts and certain plant tissues also exhibit endomitosis or endomitosis-like polyploidization as part of normal development or growth. The phenomenon is thus a tissue- and species-specific strategy to increase cell size and biosynthetic capacity.

Mechanisms underlying endomitosis involve alterations in cell cycle regulation that permit DNA replication and, in some contexts, entry into a mitotic program, while suppressing successful cytokinesis. Regulation engages cyclin-dependent kinases, components of the mitotic machinery, and the cytokinetic apparatus, with variations among different cell types. In megakaryocytes, for example, the terminal steps of cytokinesis are selectively inhibited to yield high-ploidy nuclei.

Biological significance and implications include enhanced biosynthetic capacity and cell size, supporting functions such as platelet production. While endomitosis is a normal developmental or physiological process in certain tissues, its dysregulation can contribute to genomic instability and disease in others.