Fate of senescent megakaryocytes in the bone marrow

Publisher Website
Google Scholar
Abstract
Degenerating senescent megakaryocytes were identified in mouse bone marrow by light microscopy and EM. The ultrastructural changes which occur as degeneration proceeds are characteristic of death by apoptosis, although most cells appear to round up rather than undergo fragmentation. A hitherto unreported finding in degenerating cells was the presence of bundles of .apprx. 7 nm diameter parallel filaments in nuclei and membrane-bound nuclear fragments. Structurally, they resembled bundles of filaments induced in nuclei with dimethyl sulfoxide and identified as actin. Often a bundle appeared to terminate at the inner membrane. In the cytoplasm the presence of microtubules and centrioles indicates that not all the latter organelles are lost by the megakaryocyte during platelet release. Degenerating senescent megakaryocytes are rare in the marrow of normal mice but increase in frequency during 5-fluorouracil stimulated thrombocytosis. The dying cells are eventually phagocytosed by macrophages, a process that can occur extravascularly, showing that entry of senescent megakaryocytes into the circulation is not necessary for their disposal.