Genetic analysis of novel models of thrombocytopenia and leucopenia

Three ENU-induced mutant mouse strains were obtained from the Heart, Lung, Blood and Sleep Disorders Center at The Jackson Laboratory; thrombocytopenic strains HLB381 and HLB219 and lymphopenic strain HLB156. The goal of this project was to map and characterize these strains in hopes of identifying novel mechanisms of blood dysfunction in order to better understand overall blood development.;A mutation in HLB219 was identified in the Mpl gene. This gene codes for the thrombopoietin (TPO) receptor, which along with its ligand TPO, are major regulators of platelet development. The disruption of known downstream pathways JAK-STAT and MAPK-ERK support the causative nature of the mutation while a constitutively active AKT pathway may explain the overdominance observed in mice that are heterozygous for the mutation.;In the HLB381 mouse strain a mutation in the Rasa3 gene has been identified. We have examined several stages throughout platelet development and demonstrate that the defect is not in early thrombopoiesis. Early thrombopoiesis does not seem to be affected as megakaryocytes are normal in number and hematopoietic progenitors from HLB381 are capable of competitively reconstituting irradiated mice. Platelets from HLB381 have a higher turnover rate however, the cause of the platelet loss has not been identified. Characterization of HLB381 will hopefully aid in discovering the mechanism of Rasa3's involvement.;HLB156 is a novel model of lymphopenia. These mice have a skewed CD4/CD8 ratio due to a loss of CD4+ T-cells. The B-cell population is also significantly decreased. Mapping of the mutation has been narrowed down to the centromeric region of mouse chromosome 17. Interestingly, this interval includes the mouse MHC locus. However there are no known genes in this region in which a point mutation is capable of causing MHC class I restriction. This makes HLB156 a unique model for this phenotype.;These three mouse strains demonstrate the power of ENU mutagenesis screens in generating novel models of diseases. Even in cases in which the involvement of the gene is already known, careful characterization of these strain may reveal subtle phenotypes which are unique.