Cytoskeletal organization during terminal differentiation and enucleation of mammalian erythroblasts (538.3)

Abstract

Terminal differentiation of red blood cells is a complex morphogenetic process involving chromatin condensation, cell polarization and nuclear expulsion. Microtubules are important for cell polarization, while F‐actin assembly and myosin activity are important for nuclear expulsion. In this study, we used confocal microscopy to examine erythroblasts from mouse fetal liver, adult bone marrow and phlebotomized mouse spleen. In non‐polarized erythroblasts, the F‐actin cytoskeleton is organized into a cage‐like structure surrounding the nucleus. In polarized erythroblasts from fetal liver or spleen, the F‐actin reorganizes to a bright spot at the side of the nucleus. Mitochondria are relocated from the periphery of the cell to this actin spot. This bright spot of F‐actin and the mitochondria travels with the rear of the nucleus as it is ejected. Additional foci of F‐actin are located at the neck separating the expelled nucleus from the reticulocyte. Linear cables of F‐actin are also observed in the nuclear ‘bud’ which are sometimes associated with nuclear pores. Notably, adult mouse bone marrow lacks the bright spot of F‐actin near the nucleus during nuclear expulsion. Arp2/3 and mDia2 are not associated with the bright F‐actin while myosinIIB is associated with these foci. We conclude that the actin cytoskeletal organization of enucleating erythroblasts is not conserved among different erythropoietic tissues.