The stem/progenitor landscape is reshaped in a mouse model of essential thrombocythaemia and causes excess megakaryocyte production

Frameshift mutations in CALR (calreticulin) are associated with essential thrombocythaemia (ET), but the stages at and mechanisms by which mutant CALR drives transformation remain incompletely defined. Here, we use single-cell approaches to examine the haematopoietic stem/progenitor cell (HSPC) landscape in a mouse model of mutant CALR-driven ET. We identify a trajectory linking HSCs with megakaryocytes and prospectively identify a novel intermediate population that is overrepresented in the disease state. We also show that mutant CALR drives transformation primarily from the earliest stem cell compartment, with some contribution from megakaryocyte progenitors. Finally, relative to wild-type HSCs, mutant CALR HSCs show increases in JAK-STAT signalling, the unfolded protein response, cell cycle, and a previously undescribed upregulation of cholesterol biosynthesis. Overall, we have identified a novel megakaryocyte-biased cell population that is increased in a mouse model of ET and described transcriptomic changes linking CALR mutations to increased HSC proliferation and megakaryopoiesis.
Work in the Göttgens lab is supported by the Medical Research Council (MR/M008975/1), Wellcome (206328/Z/17/Z), Blood Cancer UK (18002), and Cancer Research UK (RG83389, jointly with A.R.G). Work in the Green lab is supported by Wellcome (RG74909), WBH Foundation (RG91681), and Cancer Research UK (RG83389, jointly with B.G.).