Mammalian erythroblast enucleation requires PI3K-dependent cell polarization

Abstract

SummaryEnucleation, 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)P 2 and PtdIns(3,4,5)P 3 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.

Muscleblind-like 1 (Mbnl1) regulates pre-mRNA alternative splicing during terminal erythropoiesis

“…By overlapping the regions of alternatively skipped exons and their flanking introns with published MBNL1 CLIP-seq binding clusters, 31 we observed a significant enrichment of MBNL1 binding clusters in erythropoiesis-associated SE events (P 5 1.8 3 10…”

“…30 Therefore, our observation of MBNL motif enrichment downstream of the regulated exons suggested that MBNL proteins binding to these sites regulate inclusion of the cassette exon. By overlapping the regions of alternatively skipped exons and their flanking introns with published MBNL1 CLIP-seq binding clusters, 31 we observed a significant enrichment of MBNL1 binding clusters in erythropoiesis-associated SE events (P 5 1.8 3 10…”

KLF1-null neonates display hydrops fetalis and a deranged erythroid transcriptome

“…These include genes involved in EpoR signaling, enucleation, 61,62 and stress erythropoiesis 63 (Table 2). PLEK2 (Pleckstrin-2) and DYRK3 both have proven roles in terminal erythroid differentiation, 63,64 and both are expressed at ,10% of wildtype levels in the proband.…”

Red cell island dances: switching hands

“…3 The most striking visual aspect of this erythropoietic maturation is the last step, when the orthochromatic erythroblast goes through remarkable undulations, like a pot coming to boil, with the bulk of its cytoplasm pulling away from the nucleus until it divides into 2 very different cells. 1,4 The enucleated reticulocyte continues to mature into the functional RBC. The other cell, a pyrenocyte containing the condensed nucleus surrounded by a thin layer of cytoplasm, signals the macrophage that it is the half to be eaten by exposing phosphatidylserine on its cellular membrane.…”

“…Because KIR receptors are inhibited by autologous HLA class C molecules, many clinical investigators have chosen to infuse allogeneic NK cells to ensure that they can kill recipient tumor cells. [2][3][4] Several clinical trials have revealed the potential of NK cells as an immunotherapy, but barriers to their wider efficacy have included both their tolerance to self-major histocompatibility complex molecules and their susceptibility to immunosuppressive elements that are present at the sites of many tumors. These elements include inhibitory cytokines, myeloid-derived suppresser cells, and Tregulatory cells (Tregs).…”