ZRSR2-loss causes aberrant splicing in a JAK2V617F-driven myeloproliferative neoplasm but is not sufficient to drive disease progression I.

Myeloproliferative neoplasms (MPN), including polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF), are clonal disorders driven by mutations in hematopoietic stem cells (HSCs). JAK2V617F is the most recurrent driver mutation in MPN and results in the constitutive activation of the JAK-STAT pathway. ZRSR2-loss is reported to cause mis-splicing of U12-type introns in myelodysplastic syndromes (MDS). Loss of function mutations in ZRSR2 have been found in a JAK2V617F-driven MPNs and are associated with disease progression and poor prognosis. However, the functional contribution of ZRSR2-loss to the pathogenesis and disease progression of MPN remains unknown. Using CRISPR-Cas9, we generated concomitant ZRSR2-loss in a JAK2V617F-driven human cell line and mouse model of MPN. RNA-Seq data demonstrates that ZRSR2-loss causes aberrant splicing in both human and murine cells, with the affect being more subtle in the murine context. Gene expression analysis in murine HSCs indicates that Zrsr2-loss biases lineage differentiation priming to megakaryocytes. However, Zrsr2-loss did not alter the severity or phenotype of the MPN in Jak2V617F mice. These results indicate that Zrsr2 mutations have limited impact on disease progression of Jak2V617F -driven MPN in vivo. Consistent with this, we find that ZRSR2 mutations are more frequently identified in genetically complex MPN patients carrying other high molecular risk mutations. In total, our findings demonstrate that ZRSR2-loss causes subtle mis-splicing in JAK2V617F-driven MPN that is not sufficient to drive disease progression in the absence of other high-risk mutations.