Thrombocytogenesis by megakaryocyte; Interpretation by protoplatelet hypothesis.

Serial transmission electron microscopy of human megakaryocytes (MKs) revealed their polyploidization and gradual maturation through consecutive transition in characteristics of various organelles and others. At the beginning of differentiation, MK with ploidy 32N, e.g.

Platelet production by megakaryocytes: protoplatelet theory justifies cytoplasmic fragmentation model.

The maturation of megakaryocytes (MKs) leading to platelet production is carefully reviewed. For instance, when MK with ploidy 16N enters the maturation stage, eight centrosomes are clustered in the cell center surrounded by 16N nucleus. Each bundle of microtubules (MTs) emanated from the respective centrosome supports and organize eight equally volumed cytoplasmic compartments which together compose one single 16N MK.

In vivo platelet production from mature megakaryocytes: does platelet release occur via proplatelets?

Although platelets are universally accepted to be born from megakaryocytes (MKs), the mechanism by which platelets are formed and released from MKs in vivo remains controversial. One theory, known as the proplatelet theory, postulates that platelets are released from proplatelet processes protruding from MKs into sinusoids located in the bone marrow hematopoietic compartment. Proplatelet formation (PPF) has been observed in in vitro experiments involving detailed analyses of related molecular events.