CALR frameshift mutations in MPN patient-derived iPSCs accelerate maturation of megakaryocytes

Stem Cell Reports. 2021 Nov 9;16(11):2768-2783. doi: 10.1016/j.stemcr.2021.09.019. Epub 2021 Oct 21.


Calreticulin (CALR) mutations are driver mutations in myeloproliferative neoplasms (MPNs), leading to activation of the thrombopoietin receptor and causing abnormal megakaryopoiesis. Here, we generated patient-derived CALRins5- or CALRdel52-positive induced pluripotent stem cells (iPSCs) to establish an MPN disease model for molecular and mechanistic studies. We demonstrated myeloperoxidase deficiency in granulocytic cells derived from homozygous CALR mutant iPSCs, rescued by repairing the mutation using CRISPR/Cas9. iPSC-derived megakaryocytes showed characteristics of primary megakaryocytes such as formation of demarcation membrane system and cytoplasmic pro-platelet protrusions. Importantly, CALR mutations led to enhanced megakaryopoiesis and accelerated megakaryocytic development in a thrombopoietin-independent manner. Mechanistically, our study identified differentially regulated pathways in mutated versus unmutated megakaryocytes, such as hypoxia signaling, which represents a potential target for therapeutic intervention. Altogether, we demonstrate key aspects of mutated CALR-driven pathogenesis dependent on its zygosity, and found novel therapeutic targets, making our model a valuable tool for clinical drug screening in MPNs.

Keywords: MPN; RNA sequencing; calreticulin mutation; essential thrombocythemia; iPSCs; induced pluripotent stem cells; megakaryocytes; myelofibrosis; myeloproliferative neoplasm; transcriptional profiling.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Calreticulin / genetics*
  • Calreticulin / metabolism
  • Cell Differentiation / genetics
  • Cell Proliferation / genetics
  • Cells, Cultured
  • Flow Cytometry
  • Frameshift Mutation*
  • Gene Expression Profiling / methods
  • Humans
  • Induced Pluripotent Stem Cells / metabolism*
  • Megakaryocytes / metabolism*
  • Megakaryocytes / ultrastructure
  • Microscopy, Electron, Transmission
  • Myeloproliferative Disorders / genetics*
  • Myeloproliferative Disorders / metabolism
  • Myeloproliferative Disorders / pathology
  • Reverse Transcriptase Polymerase Chain Reaction
  • Thrombopoiesis / genetics


  • CALR protein, human
  • Calreticulin