MKI67 and myelofibrosis: Normal megakaryocytes have a low proliferation index, and healthy donor MkPs showed low expression of the proliferation marker MKI67. By contrast, MKI67 was strongly expressed in the majority of myelofibrosis MkPs and the MkP cluster showed the highest expression of MKI67 among all myelofibrosis HSPC clusters (Figure S5C) as well as an enrichment of a G2M checkpoint gene signature (Figure S5B; Table S5), suggesting that increased proliferation of MkPs may contribute to the pathological accumulation of megakaryocytes in myelofibrosis, in addition to megakaryocyte-biased hematopoiesis.