Lionel Blanc

Publications (13) View all

• Article: The scat mouse model highlights RASA3, a GTPase activating protein, as a key regulator of vertebrate erythropoiesis and megakaryopoiesis.

  Luanne L Peters, Barry H Paw, Lionel Blanc
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  ABSTRACT: Although significant progress has been made in the past decades in our understanding of bone marrow failure syndromes and anemia, many pathological conditions of unknown origin remain. Mouse models have significantly contributed to our understanding of normal erythropoiesis and the pathogenesis of erythroid disorders. Recently, we identified in the scat (severe combined anemia and thrombocytopenia) mouse model a missense mutation (G125V) in the Rasa3 gene, encoding a Ras GTPase activating protein (GAP). RASA3 is lost during reticulocyte maturation through the exosomal pathway and is therefore absent in mature erythrocytes. In wild type reticulocytes, RASA3 is bound to the plasma membrane, a prerequisite for its GAP activity, but is mislocalized to the cytosol in scat. This mislocalization leads to RASA3 loss of function and higher levels of Ras-GTP, the active form of Ras, are consistently found in scat mature red cells. Finally, RASA3 function is conserved among vertebrates, since erythropoiesis and thrombopoiesis are impaired in zebrafish in which rasa3 is knocked-down by morpholinos, and RASA3 is expressed in human erythroleukemia cells as well as in primary cells. In this commentary, we highlight the critical, conserved and non-redundant function of RASA3 in the context of vertebrate erythropoiesis and megakaryopoiesis. We notably discuss the mechanism of RASA3 downregulation and speculate on the most intriguing part of the phenotype observed in scat; the transient remission period.
  Small GTPases 12/2012; 4(1).
• Source

  Available from: Luanne L Peters

  Article: Critical function for the Ras-GTPase activating protein RASA3 in vertebrate erythropoiesis and megakaryopoiesis

  Lionel Blanc, Steven L. Ciciotte, Babette Gwynn, Gordon J. Hildick-Smith, Eric L. Pierce, Kathleen A. Soltis, Jeffrey D. Cooney, Barry H. Paw, Luanne L. Peters
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  ABSTRACT: Phenotype-driven approaches to gene discovery using inbred mice have been instrumental in identifying genetic determinants of inherited blood dyscrasias. The recessive mutant scat (severe combined anemia and thrombocytopenia) alternates between crisis and remission episodes, indicating an aberrant regulatory feedback mechanism common to erythrocyte and platelet formation. Here, we identify a missense mutation (G125V) in the scat Rasa3 gene, encoding a Ras GTPase activating protein (RasGAP), and elucidate the mechanism producing crisis episodes. The mutation causes mislocalization of RASA3 to the cytosol in scat red cells where it is inactive, leading to increased GTP-bound Ras. Erythropoiesis is severely blocked in scat crisis mice, and ∼94% succumb during the second crisis (∼30 d of age) from catastrophic hematopoietic failure in the spleen and bone marrow. Megakaryopoiesis is also defective during crisis. Notably, the scat phenotype is recapitulated in zebrafish when rasa3 is silenced. These results highlight a critical, conserved, and nonredundant role for RASA3 in vertebrate hematopoiesis.
  Proceedings of the National Academy of Sciences 07/2012; 109(30):12099-12104. · 9.68 Impact Factor
• Article: Control of erythrocyte membrane-skeletal cohesion by the spectrin-membrane linkage.

  Lionel Blanc, Marcela Salomao, Xinhua Guo, Xiuli An, Walter Gratzer, Narla Mohandas
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  ABSTRACT: Spectrin tetramer is the major structural member of the membrane-associated skeletal network of red cells. We show here that disruption of the spectrin-ankyrin-band 3 link to the membrane leads to dissociation of a large proportion of the tetramers into dimers. Noncovalent perturbation of the linkage was induced by a peptide containing the ankyrin-binding site of the spectrin beta-chain, and covalent perturbation by treatment with the thiol reagent, N-ethylmaleimide (NEM). This reagent left the intrinsic self-association capacity of the spectrin dimers unaffected and disturbed only the ankyrin-band 3 interaction. The dissociation of spectrin tetramers on the membrane into functional dimers was confirmed by the binding of a spectrin peptide directed against the self-association sites. Dissociation of the tetramers resulted, we infer, from detachment of the proximal ends of the constituent dimers from the membrane, thereby reducing their proximity to one another and thus weakening their association. The measured affinity of the interaction of the peptides with the free dimer ends on the membrane permits an estimate of the equilibrium between intact and dissociated tetramers on the native membrane. This indicates that in the physiological state the equilibrium proportion of the dissociated tetramers may be as high as 5-10%. These findings enabled us to identify an additional important functional role for the spectrin-ankyrin-band 3 link in regulating spectrin self-association in the red cell membrane.
  Biochemistry 06/2010; 49(21):4516-23. · 3.42 Impact Factor
• Article: Reticulocyte membrane remodeling: contribution of the exosome pathway.

  Lionel Blanc, Michel Vidal
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  ABSTRACT: In addition to the loss of all the internal compartments, reticulocyte maturation is characterized by an extensive membrane remodeling. Exosomal secretion contributes to this process by eliminating specific proteins. Regulation in the exosomal sorting of the water channel aquaporin-1 represents a newly described mechanism by which reticulocytes could adapt to environmental modifications. The extracellular osmotic conditions found in the peripheral circulation vs. the bone marrow could dictate a lower level of expression of aquaporin-1 on the mature red cell surface. In addition, a new mechanism for protein sorting to exosomes, involving an endogenous lectin, has been pinpointed in rat reticulocytes. Galectin-5 is secreted by a so-called alternative pathway, and could be involved in the sorting of galactoside-bearing glycoconjugates, since it was found associated with the surface of released exosomes. Secretion of exosomes during reticulocyte maturation is an integral part of the red cell differentiation program and illustrates specific mechanisms in terms of biogenesis, protein sorting and fate, which are far from completely understood and open new paths for research in the red cell physiology field.
  Current opinion in hematology 02/2010; 17(3):177-83. · 5.19 Impact Factor
• Article: Galectin-5 is bound onto the surface of rat reticulocyte exosomes and modulates vesicle uptake by macrophages.

  Céline Barrès, Lionel Blanc, Pascale Bette-Bobillo, Sabine André, Robert Mamoun, Hans-Joachim Gabius, Michel Vidal
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  ABSTRACT: Reticulocytes release small membrane vesicles termed exosomes during their maturation into erythrocytes. Exosomes are intraluminal vesicles of multivesicular endosomes released into the extracellular medium by fusion of these endosomal compartments with the plasma membrane. This secretion pathway contributes to reticulocyte plasma membrane remodeling by eliminating certain membrane glycoproteins. We show in this study that galectin-5, although mainly cytosolic, is also present on the cell surface of rat reticulocytes and erythrocytes. In addition, in reticulocytes, it resides in the endosomal compartment. We document galectin-5 translocation from the cytosol into the endosome lumen, leading to its secretion in association with exosomes. Galectin-5 bound onto the vesicle surface may function in sorting galactose-bearing glycoconjugates. Fittingly, we found that Lamp2, a major cellular glycoprotein presenting galectin-reactive poly-N-acetylactosamine chains, is lost during reticulocyte maturation. It is associated with released exosomes, suggestive of binding to galectin-5. Finally, we reveal that the uptake of rat reticulocyte exosomes by macrophages is dependent on temperature and the mechanoenzyme dynamin and that exosome uptake is decreased by adding galectin-5. These data imply galectin-5 functionality in the exosomal sorting pathway during rat reticulocyte maturation.
  Blood 11/2009; 115(3):696-705. · 9.90 Impact Factor