The fine structure of the megakaryocyte in the mouse spleen

Abstract

Sectioned megakaryocytes in the mouse spleen fixed by perfusion with PaladiSs buffered osmium tctroxidc solution have been studied with the electron microscope. Karly manifestations of platelet formation are characterized by the appearance of sheets of vesicles about 400 A in diameter, the “platelet demarcation vesicles”. These coalesce and elongate into an anastomosing system of the "platelet demarcation tubules". These, in turn, expand to form pairs of sheets constituting walls, incomplete at first, which partition the cytoplasm into many small fractions, each of which develops into a platelet. The walls formed by the fusion of vesicles and tubules are called “platelet demarcation mcmbranea”. Each member of the membrane pair is destined to serve as part of the cell membrane of the platelet. Within the cytoplasmic zones thus segregated, the cytoplasm displays components similar to those found in the mature platelets. Mitochondria, Golgi bodies, endoplasmic reticulum aud large platelet granules are described in the megakaryocyte and platelet. Centrioles are recognized in the interkinetic megakaryocytes and their fine structure is described. The classical descriptions of the megakaryocyte by Heidcnhain and by Wright ore confirmed in many respects. © 1957 S. Karger AG, Basel.