RUNX1a overexpression induced by splicing factor mutations. (A-B) RUNX1a expression levels in CD34⁺ cells from MDS (A) or MDS/MPN (B) patients with or without splicing factor (SF) mutations. **P < .01. (C) RUNX1 expression levels of 13 SRSF2 mutant (MT)–transduced clones were compared with those of 3 mock-transduced cells. Average transcript expression and standard deviation from triplicate experiments is shown. (D) RUNX1 protein expression in TF-1 cells was verified by immunoblot, and the relative protein level was quantified. RUNX1a-transfected Plat-GP cells were used as a positive control for RUNX1a protein. (E) Representative flow cytometry analysis of mock-transduced cells and SRSF2 mutant (MT)–transduced cells. (F) Phenotypic changes by RUNX1a knockdown in SRSF2 mutant–transduced cells. RUNX1a knockdown was verified by relative RUNX1a expression to GAPDH expression. BM, bone marrow.