A novel aspect of the maturational step of megakaryocytes in thrombopoiesis: bundle formation of microtubules in megakaryocytes.
We demonstrated bundle formation of microtubules both in the cytoplasmic processes and in the cytoplasm near the nucleus of cultured megakaryocytes by means of electron and immunofluorescent microscopy. To determine whether this bundle formation was related to megakaryocyte maturation, we studied the effects of recombinant human interleukin-6 (rhIL-6) in vitro and in vivo on this event. About 75% of the megakaryocytes in the bone marrow had no fibrous microtubule structures in the cytoplasm (type I), and about 25% had bundles of microtubules (type II). The formation of these bundles was promoted by rhIL-6 both in vitro and in vivo. Considerably more megakaryocytes cultured with recombinant murine (rm) IL-3 and rhIL-6 became type II than those cultured with rmIL-3 alone. Megakaryocytes from mice given rhIL-6 (10 microg/animal/d) subcutaneously also began to form bundles in proportion to an increase in platelet counts. After the administration of rhIL-6, about half of the megakaryocytes contained microtubule bundles in their cytoplasm. These results indicate that microtubule-bundle formation is one maturational event in megakaryocyte development and that rhIL-6 could accelerate this event.
Tajika
K
K
The Department of Hematology/Oncology, Institute of Medical Science, University of Tokyo, Japan.
Ikebuchi
K
K
Suzuki
E
E
Okano
A
A
Hirashima
K
K
Hirosawa
K
K
Nakahata
T
T
Asano
S
S
D000818:Animals; D001792:Blood Platelets / Q000648:ultrastructure; D001854:Bone Marrow Cells; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D003593:Cytoplasm / Q000648:ultrastructure; D005260:Female; D006801:Humans; D007377:Interleukin-3 / Q000494:pharmacology; D015850:Interleukin-6 / Q000494:pharmacology; D008533:Megakaryocytes / Q000166:cytology* / Q000187:drug effects / Q000648:ultrastructure; D051379:Mice; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D008870:Microtubules / Q000648:ultrastructure*; D011994:Recombinant Proteins / Q000494:pharmacology; D014404:Tubulin / Q000032:analysis
D007377:Interleukin-3; D015850:Interleukin-6; D011994:Recombinant Proteins; D014404:Tubulin