Physiological P95H expression causes impaired hematopoietic stem cell functions and aberrant RNA splicing in mice.

Splicing factor mutations are characteristic of myelodysplastic syndromes (MDS) and related myeloid neoplasms and implicated in their pathogenesis, but their roles in the development of MDS have not been fully elucidated. In the present study, we investigated the consequence of mutant expression using newly generated -mediated conditional knockin mice. Mice carrying a heterozygous P95H mutation showed significantly reduced numbers of hematopoietic stem and progenitor cells (HSPCs) and differentiation defects both in the steady-state condition and transplantation settings. -mutated hematopoietic stem cells (HSCs) showed impaired long-term reconstitution compared with control mice in competitive repopulation assays. Although the mutant mice did not develop MDS under the steady-state condition, when their stem cells were transplanted into lethally irradiated mice, the recipients developed anemia, leukopenia, and erythroid dysplasia, which suggests the role of replicative stress in the development of an MDS-like phenotype in -mutated mice. RNA sequencing of the -mutated HSPCs revealed a number of abnormal splicing events and differentially expressed genes, including several potential targets implicated in the pathogenesis of hematopoietic malignancies, such as , , , , , and Among the mutant -associated splicing events, most commonly observed were the enhanced inclusion and/or exclusion of cassette exons, which were caused by the altered consensus motifs for the recognition of exonic splicing enhancers. Our findings suggest that the mutant leads to a compromised HSC function by causing abnormal RNA splicing and expression, contributing to the deregulated hematopoiesis that recapitulates the MDS phenotypes, possibly as a result of additional genetic and/or environmental insults.