Hematopoietic-specific beta 1 tubulin participates in a pathway of platelet biogenesis dependent on the transcription factor NF-E2

The cellular and molecular bases of platelet release by terminally differen tiated megakaryocytes represent important questions in cell biology and hem atopoiesis. Mice lacking the transcription factor NF-E2 show profound throm bocytopenia, and their megakaryocytes fail to produce proplatelets, the mic rotubule-based precursors of blood platelets. Using mRNA subtraction betwee n normal and NF-E2-deficient megakaryocytes, cDNA was isolated encoding bet a 1 tubulin, the most divergent beta 1 tubulin isoform. In NF-E2-deficient megakaryocytes, beta 1 tubulin mRNA and protein are virtually absent. The e xpression of beta 1 tubulin Is exquisitely restricted to platelets and mega karyocytes, where it appears late in differentiation and localizes to micro tubule shafts and coils within proplatelets. Restoring NF-E2 activity in a megakaryoblastic cell line or in NF-E2-deficient primary megakaryocytes res cues the expression of beta 1 tubulin. Reexpressing beta 1 tubulin in isola tion does not, however, restore proplatelet formation in the defective mega karyocytes, indicating that other critical factors are required; indeed, ot her genes identified by mRNA subtraction also encode structural and regulat ory components of the cytoskeleton. These findings provide critical mechani stic links between NF-E2, platelet formation, and selected microtubule prot eins, and they also provide novel molecular insights into thrombopoiesis. ( Blood. 2000;96:1366-1373) (C) 2000 by The American Society of Hematology.