Working model of the erythroblast enucleation process. Microtubules assist in the establishment of polarity in orthochromatic erythroblasts. Actin, under the control of Rac GTPases, assembles with myosin to form an actomyosin ring in the “cleavage furrow” between nucleus and incipient reticulocyte. The phosphorylation of MRLC allows the actomyosin complex to contract. Lipid rafts, containing and coordinated by Rac GTPases, coalesce in the cleavage furrow serving possibly to position the actomyosin ring properly and to target secretory vesicles toward creation of new membrane and separation of the nucleus.