This H794L point substitution in the C terminus domain of the RASA3 GTPas-activating protein causes leukopenia, splenomegaly due to a large increase in megakaryocytes in the red pulp, and thrombocytopenia due to faster platelet turnover, but the hematocrit and red blood cell counts are normal. This is a very mild phenotype compared with the prenatal and perinatal lethality that occurs in Rasa3 null homozygotes and a somewhat less severe phenotype than that caused by the Rasa3scat mutation. This mutant may provide a model for studying some aspects of aplastic anemia.Read More +
This hypomorphic mutation was initially identified in a phenotypic screen of third generation mice (G3) from ENU mutagenized males. A 6-week-old male maintained on standard chow was found to have a platelet count of 24 x 103 cells/ul, which is approximately 98% lower than controls. RASA3 is a RAS and RAP1 GTPase-activating protein that moves between the cytosol and the plasma membrane and when localized to the platelet plasma membrane it inhibits platelet activation in homeostatic balance against RASGRP2. This ENU-induced point mutation causes an H794L substitution in the C terminus domain which results in a reduction of RASA3 expression in homozygotes. Western blotting failed to detect RASA3 in red cell membranes or whole red blood cells of homozygotes and RASA3 is found in considerably reduced levels in platelets. Homozyogtes have severe thrombocytopenia and leukopenia, with increased platelet volume, but differ from Rasa3scat or null alleles of Rasa3 in viability and lack of severe anemia. Rasa3hlb381 heterozygous intercrosses generate the normal Mendelian ratio of mutants with no pallor or bruising, and the hematocrit and red blood cell counts are normal, although there is a comparatively mild compensated anemia with reticulocytosis and increased spleen weight, but normal splenic architecture. Heterozygotes were found to have normal platelet and leukocyte counts, but Rasa3hlb381/scat compound heterozygotes displayed severe thrombocytopenia. The half-life for circulating platelets in Rasa3hlb381 homozygotes was found to be only 14 hours compared with 55 hours in wildtype controls, these platelets have increased activated RAP1-GTP and activated alphaII/Beta3 integrin and the number of reticulated (immature) platelets was more than 3 times higher than normal, indicative of a high rate of both platelet destruction and production of new platelets. There is a significant increase in the number of megakaryocytes in the bone marrow and splenic red pulp. This is all consistent with reduced platelet survival/increased clearance and rate of platelet production to compensate for the continued loss. (Stephanini et al., 2015; Robledo et al., 2020.)
Following multidose ethylnitrosourea (ENU) treatments to induce mutations in male founder C57BL/6J mice (Stock No. 000664), a forward genetic screen was utilized to identify phenotypic deviants in complex heart, lung, blood, and sleep disorders, at the Mouse Heart, Lung, Blood, and Sleep Disorders (HLBS) Center at The Jackson Laboratory. hlb381 was mapped to Chromosome 8 and later determined to be a H794L mutation in Rasa3. This mutation was maintained coisogenic on C57BL/6J and sibling intercrossed to homozygosity. Embryos were generated from homozygous females crossed to homozygous males at generations N3F4 through N3F6.
|Allele Name||heart, lung and blood 381|
|Allele Type||Chemically induced (ENU) (Hypomorph)|
|Allele Synonym(s)||Rasa3H794L; Rasa3hlb|
|Gene Symbol and Name||Rasa3, RAS p21 protein activator 3|
|Strain of Origin||C57BL/6J|
|Molecular Note||ENU mutagenesis induced an A to T point mutation that results in the amino acid substitution of leucine for histidine at position 794 (H794L), reduced expression of the protein is found in platelets from homozygotes but not heterozygotes, and Western blots fail to detect this protein in reticulocytes or mature red blood cells.|
This strain can be maintained by intercrossing homozygotes.
When using the HLB381 mouse strain in a publication, please cite the originating article(s) and include JAX stock #005343 in your Materials and Methods section.