Differential Effects of RASA3 Mutations on Hematopoiesis are Profoundly Influenced by Genetic Background and Molecular Variant

Abstract

Studies of the severely pancytopenic scat mouse model first demonstrated the crucial role of RASA3, a dual RAS and RAP GTPase activating protein (GAP), in hematopoiesis. RASA3 is required for survival in utero; germline deletion is lethal at E12.5-13.5 due to severe hemorrhage and decreased fetal liver erythropoiesis. Conditional deletion in hematopoietic stem and progenitor cells (HSPCs) using Vav-Cre recapitulates the null phenotype demonstrating that RASA3 is required at the stem and progenitor level to maintain blood vessel development and integrity and effective blood production. In adults, bone marrow blood cell production and spleen stress erythropoiesis are suppressed significantly upon induction of RASA3 deficiency, leading to pancytopenia and death within two weeks. Notably, RASA3 missense mutations in mouse models scat (G125V) and hlb381 (H794L) show dramatically different hematopoietic consequences specific to both genetic background and molecular variant. Global transcriptomic studies in scat suggest potential targets to ameliorate disease progression. Author SummaryHematopoiesis is the process by which blood cells are formed. The individual must have a normal complement of red blood cells to prevent anemia, platelets to control bleeding, and white blood cells to maintain immune functions. All blood cells are derived from hematopoietic stem cells that differentiate into progenitor cells that then develop into mature circulating cells. We studied several mouse strains carrying different mutations in RASA3. We show that RASA3 is required at the earliest stages of blood formation, the stem and progenitor cells, and that the complement of genes other than RASA3, or the genetic background of the mutant strain, profoundly alters the overall effect on blood formation. Further, the molecular nature of the mutation in RASA3 also has a profound and independent effect on overall blood formation. One strain, designated scat, suffers cyclic anemia characterized by severe anemic crisis episodes interspersed with remissions where the anemia significantly improves. Comparison of scat crisis and remission hematopoietic stem and progenitor cells reveals striking differences in gene expression. Analyses of these expression differences provide clues to processes that potentially drive improvement of anemia in scat and provide new avenues to pursue in future studies to identify novel therapeutics for anemia.