An ENU-induced mouse mutant of SHIP1 reveals a critical role of the stem cell isoform for suppression of macrophage activation

ArticleinBlood 117(20):5362-71 · March 2011with4 Reads
DOI: 10.1182/blood-2011-01-331041 · Source: PubMed
Abstract
In a recessive ENU mutagenesis screen for embryonic lethality, we identified a mouse pedigree with a missense mutation of SHIP1 (SHIP1(el20)) leading to an amino acid substitution I641T in the inositol-5'-phosphatase domain that represses phosphatidylinositol-3-kinase signaling. Despite detectable expression of functional SHIP1 protein, the phenotype of homozygous SHIP1(el20/el20) mice was more severe than gene-targeted SHIP1-null (SHIP1(-/-)) mice. Compared with age-matched SHIP1(-/-) mice, 5-week-old SHIP1(el20/el20) mice had increased myeloid cells, serum IL-6 levels, marked reductions in lymphoid cells, and died by 7 weeks of age with infiltration of the lungs by activated macrophages. Bone marrow transplantation demonstrated that these defects were hematopoietic-cell-autonomous. We show that the el20 mutation reduces expression in SHIP1(el20/el20) macrophages of both SHIP1 and s-SHIP, an isoform of SHIP1 generated by an internal promoter. In contrast, SHIP1(-/-) macrophages express normal levels of s-SHIP. Compound heterozygous mice (SHIP1(-/el20)) had the same phenotype as SHIP1(-/-) mice, thus providing genetic proof that the more severe phenotype of SHIP1(el20/el20) mice is probably the result of concomitant loss of SHIP1 and s-SHIP. Our results suggest that s-SHIP synergizes with SHIP1 for suppression of macrophage activation, thus providing the first evidence for a role of s-SHIP in adult hematopoiesis.
    • "There is a growing evidence that missense, nonsense and silent mutations affect the consensus sequence of exonic cis-elements such as exonic splice enhancers (ESE) and exonic splice silencers (ESS) that are important for correct splice-site identification (Cartegni et al., 2002; Gorlov et al., 2003; Gorlov et al., 2004; Bashyam et al., 2010; Jin et al., 2012). A missense mutation in hematopoietic-restricted Src homology 2-containing inositol-5?-phos- phatase (SHIP1) resulted in markedly reduced SHIP1 protein and thus reduced RNA levels as this presumably affected the RNA stability (Nguyen et al., 2011 ). Thus it is important to evaluate the exonic single nucleotide substitutions for assessing their possible consequences on pre-mRNA processing (Cartegni et al., 2002). "
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