title: Mammalian erythroblast enucleation requires PI3K-dependent cell polarization.
abstract: Enucleation, the final step in terminal differentiation of mammalian red blood cells, is an essential process in which the nucleus surrounded by the plasma membrane is budded off from the erythroblast to form a reticulocyte. Most molecular events in enucleation remain unclear. Here we show that enucleation requires establishment of cell polarization that is regulated by the microtubule-dependent local activation of phosphoinositide 3-kinase (PI3K). When the nucleus becomes displaced to one side of the cell, actin becomes restricted to the other side, where dynamic cytoplasmic contractions generate pressure that pushes the viscoelastic nucleus through a narrow constriction in the cell surface, forming a bud. The PI3K products PtdIns(3,4)P₂ and PtdIns(3,4,5)P₃ are highly localized at the cytoplasmic side of the plasma membrane. PI3K inhibition caused impaired cell polarization, leading to a severe delay in enucleation. Depolymerization of microtubules reduced PI3K activity, resulting in impaired cell polarization and enucleation. We propose that enucleation is regulated by microtubules and PI3K signaling in a manner mechanistically similar to directed cell locomotion.
authors.affiliation: Temasek Life Sciences Laboratory, 1 Research Link, National University of Singapore, 117604 Singapore.
authors.forename: Junxia
authors.initials: J
authors.lastname: Wang
authors.forename: Tzutzuy
authors.initials: T
authors.lastname: Ramirez
authors.forename: Peng
authors.initials: P
authors.lastname: Ji
authors.forename: Senthil Raja
authors.initials: SR
authors.lastname: Jayapal
authors.forename: Harvey F
authors.initials: HF
authors.lastname: Lodish
authors.forename: Maki
authors.initials: M
authors.lastname: Murata-Hori
mesh_terms: D000818:Animals; D001692:Biological Transport; D002467:Cell Nucleus / Q000502:physiology*; D016764:Cell Polarity; D002478:Cells, Cultured; D003593:Cytoplasm / Q000502:physiology; D004900:Erythroblasts / Q000166:cytology* / Q000201:enzymology* / Q000502:physiology; D004920:Erythropoiesis; D051379:Mice; D008810:Mice, Inbred C57BL; D022101:Microtubule-Organizing Center / Q000502:physiology; D008870:Microtubules / Q000502:physiology; D058539:Phosphatidylinositol 3-Kinase / Q000378:metabolism*
chemical_list: D058539:Phosphatidylinositol 3-Kinase