Aberrant alternative splicing in u2af1/tet2 double mutant mice contributes to major hematological phenotypes

Abstract

Mutations in splicing factors are recurrent somatic alterations identified in myelodysplas-tic syndromes (MDS) and they frequently coincide with mutations in epigenetic factors. About 25% of patients present concurrent mutations in such pathways, suggesting a cooperative role in the pathogenesis of MDS. We focused on the splicing factor U2AF1 involved in the recognition of the 3′ splice site during pre‐mRNA splicing. Using a CRISPR/Cas9 system, we created heterozygous mice with a carboxy‐terminal truncated U2af1 allele (U2af1mut/+), studied the U2af1mut/+ hematopoi-etic system, and did not observe any gross differences in both young (12‐13 weeks) and old (23 months) U2af1mut/+ mice, except for a reduction in size of approximately 20%. However, hematopoi-etic stem/progenitor cells lacked reconstitution capacity in transplantation assays and displayed an aberrant RNA splicing by RNA sequencing. We also evaluated U2af1mut/+ in conjunction with Tet2‐deficiency. Novel double mutant U2af1mut/+ Tet2−/− mice showed increased monogranulocytic precur-sors. Hematopoietic stem/progenitor cells were also enhanced and presented functional and tran-scriptomic alterations. Nonetheless, U2af1mut/+ Tet2−/− mice did not succumb to MDS disease over a 6‐month observation period. Collectively, our data suggest that cooperation between mutant U2af1 and Tet2 loss is not sufficient for MDS initiation in mice.