Tmod3-/- mouse fetal liver compared with wild type

Tropomodulins (Tmods) cap the pointed ends of actin filaments in erythroid and nonerythoid cell types. Targeted deletion of mouse Tmod3 leads to embryonic lethality at E14.5-E18.5, with anemia due to defects in definitive erythropoiesis in the fetal liver. BFU-E and CFU-E colony numbers are greatly reduced, indicating defects in progenitor populations. Flow-cytometry of fetal liver erythroblasts shows late stage populations are also decreased, including reduced percentages of enucleated cells. AnnexinV staining indicates increased apoptosis of Tmod3-/- erythroblasts, and cell cycle analysis reveals that there are more Ter119hi cells in S-phase in Tmod3-/- embryos. Notably, enucleating Tmod3-/- erythroblasts are still in the process of proliferation, suggesting impaired cell cycle exit during terminal differentiation. Tmod3-/- late erythroblasts often exhibit multi-lobular nuclear morphologies and aberrant F-actin assembly during enucleation. Furthermore, native erythroblastic island formation was impaired in Tmod3-/- fetal livers, with Tmod3 required in both erythroblasts and macrophages. In conclusion, disruption of Tmod3 leads to impaired definitive erythropoiesis, due to reduced progenitors, impaired erythroblastic island formation, and defective erythroblast cell cycle progression and enucleation. Tmod3-mediated actin remodeling may be required for erythroblast-macrophage adhesion, coordination of cell cycle with differentiation, and F-actin assembly and remodeling during erythroblast enucleation.

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Sui Z, Nowak RB, Bacconi A, Kim NE, Liu H, Li J, Wickrema A, An XL, Fowler VM