Survivin: a new player during erythroblast maturation.

Enucleation of erythroblasts is a phenomenon unique to mammals. During their terminal stage of differentiation, mammalian erythroblasts exit the cell cycle and enucleate. They complete their terminal differentiation and enucleation in “erythroid niches” composed of erythroblastic islands nested in extracellular matrix proteins. It has been recently reported that, in the very last stage of enucleation, not only proteins but also specialized regions of the lipid bilayer, known as lipid rafts, as well as organelles participate in the extrusion of the nucleus. Approximately 120 million reticulocytes are generated each minute in our body. Macrophages phagocyte and recycle a similar number of extruded nuclei and other organelles, such as mitochondria. In addition, wastes in the reticulocyte are digested through autophagy and extruded via exosomes. Keerthivasan and colleagues shed new light on the functional relationship between enucleation and vesicle trafficking by identifying a novel role for the apoptosis inhibitor, survivin.