Origin of the Early Megakaryopoietic Progenitor Cell and Further Polyploidization in the Thrombopoietic Cell Series. Phase-Contrast Observations of Human Bone Marrow

Abstract

Continuous observation of living cells by phase-contrast time lapse microcinematography revealed different origins of multinuclear cells and cells with lobed nuclei in the hematopoietic progenitor cell series, which must be classified as megakaryoblasts, the determinated progenitor cells of the megakaryopoietic series. Hematopoietic progenitor cells with single nuclei of nuclear diameter 5–13 μm, the promegakaryoblasts, may become polyploid by various means: by postmitotic cytoplasmic fusion, by consecutive nuclear fusion, by endomitosis, or by nuclear amitosis or lobe formation presumably after endoreduplication and nuclear growth. Including amitotic nuclear division in the mitotic rate of normal progenitor cells nearly the half of all these cells in G₂ phase (0.4) produce in vitro octoploid megakaryoblasts, respectively osteoclasts. Thrombopoietin-rich sera in the medium enhance the mitotic index of the hematopoietic progenitor cell line from 0.1 to 0.25, but do not change the proportion of polyploid mitoses.

Documentation of Normal and Leukemic Myelopoietic Progenitor Cells with High-Resolution Phase-Contrast Time-Lapse Cinematography

“…In these cases the cells are called BFU E instead of myeloblasts [33]. As already mentioned, a number of disturbances during the course of mitosis in the progenitor cell line leads to the formation of polyploid cells (megakaryocytic cell line) although in aITP and thrombocytosis mitotic cell doubling preponderates [16,34]. The polyploidization-inducing lymphocytes show their close affiliation with the progenitor cell line.…”

Human Megakaryoblastic Proliferation and Differentiation Events Observed by Phase-Contrast Cinematography

“…In 9 cells, the de formed nucleus was rotating and partitioned in 3-6 lobes without fission of the nucleus, while in 16 cells, indenta tions were followed by division of the nucleus and the nucleolus into two parts (nuclear amitosis), as described previously [2], Prolonged observation showed a normal motility and never a subsequent partition of the cell. This form of nuclear polyploidization was particularly ob served in normal bone marrow specimens (table 2).…”

“…The formation of polyploid 4 and more N cells may be achieved by several mechanisms, all of which appear to be realized in the megakaryocytic cell lineage [2]. The small megakaryoblasts ( fig.…”

“…Our observations suggest KARGER. that polyploidization during megakaryocytogenesis re sults from a number of different mechanisms [2]. Cell multiplication by usual mitoses and maturation from promegakaryoblasts to megakaryoblasts and to promega karyocytes was documented, as well.…”

“…This form of nuclear polyploidization was particularly ob served in normal bone marrow specimens (table 2). [2], In 2 cells of CML blood cell cultures, chromosomal structures ap peared in a bright, rapidly enlarging nucleus with an 6 . A A binucleated cell is contacted (below) by a moving lymphocyte.…”