asxl1 C-terminal truncation and SRSF2 mutation drive leukemogenesis via immune reprogramming

Acute myeloid leukemia (AML) carrying mutations pertinent to chromatin-modification and spliceosome represents an aggressive subtype with poor prognosis.Specifically, mutations of genes encoding additional sex combs-like 1 (ASXL1), a member of the polycomb protein family [1, 2], and serine/arginine-rich splicing factor 2 (SRSF2), a member of RNA splicing machinery [3,4], are frequently found in myeloid neoplasms [5][6][7].The cooccurrence of ASXL1 and SRSF2 P95H mutations leads to a significantly worse prognosis than having either mutation alone, indicating a synergistic effect in leukemogenesis [1].Mice engineered with the Asxl1 C-terminal truncation and the Srsf2 P95H mutation developed leukemia characterized by a myeloid-biased hematopoietic stem cell (HSC) pool and a malignant transcriptomic signature [1].These findings correlate mutation combinations to leukemia progression, but the mechanisms driving leukemogenesis remain unclear, hindering targeted therapy development.Herein, we developed a zebrafish model carrying both mutations to gain new insights into the mechanisms underpinning the pathogenic synergism between asxl1 and SRSF2 P95H .By crossing zebrafish with a C-terminal truncation mutation in asxl1 [8] (referred to as "A") with Tg(Runx1: SRSF2 P95H ) (referred to as "S") transgenic zebrafish, which expresses the SRSF2 P95H mutation under the Runx1 promoter in the HSPC population [9] (Supplementary Fig. 1), we have generated a double mutant zebrafish model (referred to as "SA").At the embryonic stage, SA embryos showed a significant increase in myeloid progenitors, as shown by pu.1 expression, which was higher than asxl1 deletion or transgenic SRSF2 P95H alone (Fig. 1A,E).At 9-12 months, these double mutants exhibited an expanded monocytic compartment in their kidney marrow (KM), compared with the single mutants, as indicated by increased fluoride-sensitive NSE expression (Fig. 1B,F).Additionally, they exhibited higher KM blast