Rho GTPases in erythroid maturation.
OBJECTIVE
This review summarizes our current understanding of the roles of Rho GTPases in early erythropoiesis, downstream of cytokine signaling, and in terminal erythroblast maturation and enucleation, as master regulators of the cytoskeleton and cytokinesis.


RESULTS
Similarities of structural and signaling requirements of erythroblast enucleation with the cytokinesis process have been confirmed and expanded in the last year, suggesting that enucleation is a form of asymmetric cell division. Myosin, the classic actin partner in cytokinesis, was shown to play an essential role in enucleation. Studies with multispectral high-speed cell imaging in flow demonstrated a sequential process requiring establishment of polarity through a unipolar microtubule spindle in orthochromatic erythroblasts, followed by Rac-directed formation of a contractile actomyosin ring and coalescence of lipid rafts between reticulocyte and pyrenocyte, steps which reiterate the choreography of cytokinesis. mDia2, a Rho effector known to play a role in enucleation, was also found essential for erythroblast cytokinesis as its deficiency in mice caused failure of primitive erythropoiesis and embryonic death.


CONCLUSIONS
Further elucidation of the role of Rho GTPases in the erythroid lineage development may reveal potential targets for improving red blood cell production in vivo and in vitro.
Cancer and Blood Diseases Institute, Cincinnati Children's Hospital Medical Center, University of Cincinnati College of Medicine, Cincinnati, Ohio, USA.
Theodosia A
TA
Kalfa
Yi
Y
Zheng
D000818:Animals; D001692:Biological Transport; D016207:Cytokines / Q000502:physiology; D048749:Cytokinesis / Q000502:physiology; D003599:Cytoskeleton / Q000502:physiology*; D004900:Erythroblasts / Q000502:physiology*; D004920:Erythropoiesis / Q000502:physiology*; D006801:Humans; D015398:Signal Transduction / Q000502:physiology; D020741:rho GTP-Binding Proteins / Q000502:physiology*
D016207:Cytokines; D020741:rho GTP-Binding Proteins