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Blood Cancer J. 2016 Oct 7;6(10):e481. doi: 10.1038/bcj.2016.83.

Expression of CALR mutants causes mpl-dependent thrombocytosis in zebrafish.

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Graduate Institute of Oncology, National Taiwan University College of Medicine, Taipei, Taiwan.
Division of Hematology and Oncology, Department of Internal Medicine, MacKay Memorial Hospital, Taipei, Taiwan.
Laboratory of Good Clinical Research Center, Department of Medical Research, MacKay Memorial Hospital, Tamsui District, New Taipei City, Taiwan.
Department of Medicine, MacKay Medical College, New Taipei City, Taiwan.
Institute of Molecular and Cellular Biology, National Tsing-Hua University, Hsinchu, Taiwan.
Division of Hematology, Department of Internal Medicine, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei, Taiwan.
Department of Laboratory Medicine, National Taiwan University Hospital, Taipei, Taiwan.


CALR mutations are identified in about 30% of JAK2/MPL-unmutated myeloproliferative neoplasms (MPNs) including essential thrombocythemia (ET) and primary myelofibrosis. Although the molecular pathogenesis of CALR mutations leading to MPNs has been studied using in vitro cell lines models, how mutant CALR may affect developmental hematopoiesis remains unknown. Here we took advantage of the zebrafish model to examine the effects of mutant CALR on early hematopoiesis and model human CALR-mutated MPNs. We identified three zebrafish genes orthologous to human CALR, referred to as calr, calr3a and calr3b. The expression of CALR-del52 and CALR-ins5 mutants caused an increase in the hematopoietic stem/progenitor cells followed by thrombocytosis without affecting normal angiogenesis. The expression of CALR mutants also perturbed early developmental hematopoiesis in zebrafish. Importantly, morpholino knockdown of mpl but not epor or csf3r could significantly attenuate the effects of mutant CALR. Furthermore, the expression of mutant CALR caused jak-stat signaling activation in zebrafish that could be blocked by JAK inhibitors (ruxolitinib and fedratinib). These findings showed that mutant CALR activates jak-stat signaling through an mpl-dependent mechanism to mediate pathogenic thrombopoiesis in zebrafish, and illustrated that the signaling machinery related to mutant CALR tumorigenesis are conserved between human and zebrafish.

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