UNDERSTANDING THE BASIS OF CO-OPERATIVITY BETWEEN SRSF2P95H MUTATION AND TET2 DELETION IN A MOUSE MODEL OF MYELOPROLIFERATIVE/MYELODYSPLASTIC SYNDROMES

Abstract

Myelodysplastic syndromes (MDS) are a collection of heterogeneous clonal stem cell disorders that lead to ineffective haematopoiesis and multi-lineage cytopenia. Mutations of SRSF2, a spliceosome component, are found in high-risk MDS (12-15%) and chronic myelomonocytic leukaemia (CMML; 40-50%)- an aggressive myeloproliferative neoplasm (MPN). In patients, SRSF2P95H mutation frequently co-occurs with mutations in other pathways, such as DNA methylation, chromatin modification and transcription. In CMML, co-occurrence of SRSF2 and TET2 mutation is highly prevalent (50-60%) and confers a worse overall survival (OS). TET2 is a demethylating enzyme that promotes myeloid leukaemia when inactivated. Here, we describe the generation and characterisation of a conditional Srsf2P95H knock-in and Tet2 knock-out double mutant mouse model. Using hSclCre-mediated activation and a Rosa26eYFP reporter, we established Srsf2P95H with either Tet2 heterozygous (Srsf2P95H/+ Tet2-/+) or Tet2 homozygous deletion (Srsf2P95H/+ Tet2-/-). Twenty weeks post activation, Srsf2P95H/+ Tet2-/- mice have exacerbated peripheral granulocytosis and monocytosis but a normal B cell number, compared to Srsf2P95H/+ single mutant mice. In the eYFP+ bone marrow fraction, Srsf2P95H/+ Tet2-/- mice exhibit a decreased number of long-term haematopoietic stem cells (LT-HSC) similar to Srsf2P95H/+ single mutant mice. However, there is an increased number of short-term haematopoietic stem cells (ST-HSC) and multipotent progenitors (MPP) in the Srsf2P95H/+ Tet2-/- mice compared to Srsf2P95H/+ mice. Srsf2P95H/+ Tet2-/+ heterozygous mice exhibit a similar, although milder phenotype. Overall, characterisation of Srsf2P95H/+ Tet2-/- double mutant mice indicated that having Tet2 deletion in addition to Srsf2P95H/+ exacerbates the myeloid bias but also preserves the lymphoid lineages and early progenitor cells.