Tmod3 participates in platelet formation and sizing in mouse fetal liver (278.9)

Tropomodulins (Tmod) bind tropomyosin and cap the pointed ends of actin filaments. Tmod3 is the only Tmod isoform detected in human and mouse platelets. To study its function in platelets we have examined platelets from Tmod3-/- embryos, which are embryonic lethal (Sui Z et al. 2013. Blood in press), and occasionally display hemorrhage. The platelets in the peripheral blood from E14.5 Tmod3-/- embryos are larger than normal, indicating that platelet formation and sizing might be impaired without Tmod3. Both X-gal staining and immunostaining with β-gal antibodies show that Tmod3 is expressed at relatively high levels in megakaryocytes (MKs) of fetal livers. However, MK numbers are not significantly reduced in Tmod3-/- fetal livers, and ploidy analysis of Tmod3-/- MKs shows only a slight increase in the 8N MK population, suggesting that MK differentiation is not affected without Tmod3. Immunostaining of Tmod3 shows that Tmod3 is highly expressed in MK pseudopods and is partially co-localized with F-actin in...