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Abstract
A previous investigation detailed the pathology of platelets in a family with the X-linked GATA-1 G208S mutation causing dyserythropoiesis and megathrombocytopenia. The present study has used ultrastructural immunocytochemistry, cytochemistry, and tannic acid staining to answer questions raised in the original investigation. Earlier studies, as well as ours, had shown that GATA-1 megathrombocytes are hypogranular, but did not definitively determine which organelles are decreased. Cytochemical localization of aryl sulfatase revealed that lysosomes were present in normal numbers, and the whole mount technique showed a normal frequency of dense bodies rich in arlenine nucleotides and serotonin. Thus α granules were the only organelles deficient in GATA-1 platelets. Tannic acid staining confirmed that the membranes wrapped around each other to form tubular inclusions come from elements of the dense tubular system. The unique tubular membrane inclusions in GATA-1 megathrombocytes, thought originally to derive from endoplasmic reticulum in the parent cell, were shown to be in direct continuity with elements of the surface connected open canalicular system (OCS), and to drive from the demarcation membrane system (DMS) of the megakaryocyte. Platelets in platelets and platelets in platelets in platelets were independent cells, and not derived by cytoplasmic sequestration in the enclosing macrothrombocytes. Fully spread GATA-1 platelets incubated with fibrinogen coated gold (Fgn/Au) particles before or after fixation bound as many Fgn/Au particles as normal spread platelets and moved the Fgn/Au- GPIIb/IIIa complexes from peripheral margins to cell centers and into channels of the OCS as efficiently. Exposure of spread normal platelets to bovine vWF resulted in coverage of the surface from edge to edge with multimers detected by anti-vWF antibody and protein A gold. Spread GATA-1 platelets bound very few vWF multimers, which were much smaller in size than those on normal spread cells, but were able to move then to cell centers. These findings support the concept that GATA-1 platelets are macrothrombocytes because they are not able to detach normally from each other during separation from megakaryocyte proplatelets. The marked decrease in the number and abnormal distribution of GPIb/IX receptors may play a role in GATA-1 megathrombocyte formation.