Frameshift mutations in CALR (calreticulin) are associated with essential thrombocythemia (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 hematopoietic stem/progenitor cell landscape in a mouse model of mutant CALR-driven ET. We identify a trajectory linking hematopoietic stem cells (HSCs) with megakaryocytes and prospectively identify a previously unknown 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. Last, relative to wild-type HSCs, mutant CALR HSCs show increases in JAK-STAT signaling, the unfolded protein response, cell cycle, and a previously undescribed up-regulation 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.

CALR （钙网蛋白）中的移码突变与原发性血小板增多症（ET）相关，但突变 CALR 驱动转化的阶段和机制仍未完全确定。在这里，我们使用单细胞方法来检查突变 CALR 驱动的 ET 小鼠模型中的造血干/祖细胞景观。我们确定了连接造血干细胞（HSC）与巨核细胞的轨迹，并前瞻性地确定了在疾病状态下比例过高的先前未知的中间群体。我们还表明，突变的 CALR 主要驱动最早的干细胞区室的转化，其中一些来自巨核细胞祖细胞的贡献。最后，相对于野生型 HSC，突变型 CALR HSC 表现出 JAK-STAT 信号传导、未折叠蛋白反应、细胞周期以及先前未描述的胆固醇生物合成上调的增加。总体而言，我们发现了一种新的偏向巨核细胞的细胞群，该细胞群在 ET 小鼠模型中增加，并描述了将CALR突变与 HSC 增殖和巨核细胞生成增加联系起来的转录组变化。