Abstract
Somatic mutations in the calreticulin (CALR) gene are associated with approximately 30% of essential thrombocythemia (ET) and primary myelofibrosis (PMF). CALR mutations, including the two most frequent 52 bp deletion (del52) and 5 bp insertion (ins5), induce a frameshift to the same alternative reading frame generating new C-terminal tails. In patients, del52 and ins5 induce two phenotypically distinct myeloproliferative neoplasms (MPNs). They are equally found in ET, but del52 is more frequent in PMF. We generated heterozygous and homozygous conditional inducible knock-in (KI) mice expressing a chimeric murine CALR del52 or ins5 with the human mutated C-terminal tail to investigate their pathogenic effects on hematopoiesis. Del52 induces greater phenotypic changes than ins5 including thrombocytosis, leukocytosis, splenomegaly, bone marrow hypocellularity, megakaryocytic lineage amplification, expansion and competitive advantage of the hematopoietic stem cell compartment. Homozygosity amplifies these features, suggesting a distinct contribution of homozygous clones to human MPNs. Moreover, homozygous del52 KI mice display features of a penetrant myelofibrosis-like disorder with extramedullary hematopoiesis linked to splenomegaly, megakaryocyte hyperplasia and the presence of reticulin fibers. Overall, modeling del52 and ins5 mutations in mice successfully recapitulates the differences in phenotypes observed in patients.
Highlights
Somatic mutations in the calreticulin (CALR) gene are associated with approximately 30% of essential thrombocythemia (ET) and primary myelofibrosis (PMF)
Essential thrombocythemia (ET) and primary myelofibrosis (PMF) are two disorders of the megakaryocytic lineage defined by an increased level of circulating platelets in ET and by megakaryocytic hyperplasia/ dysplasia accompanied by the development of fibrosis in the bone marrow (BM) in PMF
Using an Ab directed against the mutated Cterminal tail (CALR-Cter) that does not detect endogenous CALR wt, there seems to be less CALR del[52] than CALR ins[5] in the homozygous cells, in accordance with the difference of protein levels revealed with the CALR-tot Ab
Summary
Somatic mutations in the calreticulin (CALR) gene are associated with approximately 30% of essential thrombocythemia (ET) and primary myelofibrosis (PMF). Del[52] induces greater phenotypic changes than ins[5] including thrombocytosis, leukocytosis, splenomegaly, bone marrow hypocellularity, megakaryocytic lineage amplification, expansion and competitive advantage of the hematopoietic stem cell compartment Homozygosity amplifies these features, suggesting a distinct contribution of homozygous clones to human MPNs. homozygous del[52] KI mice display features of a penetrant myelofibrosis-like disorder with extramedullary hematopoiesis linked to splenomegaly, megakaryocyte hyperplasia and the presence of reticulin fibers. Several other models have been published including a human del[52] transgenic (TG) mouse[10], CRISPR-Cas9-mediated both murine del[19] and murine del5211, and murine del[61] knock-in (KI) mice[12] as well as an inducible conditional KI expressing murine CALR with the human del52-mutated end tail[13] None of these studies directly compare the effects of in vivo physiopathological expression of the two most frequent types of CALR mutations on hematopoiesis, nor do they address the disease outcomes of ins[5] or type 2-like mutant expression in mice. Our KI mice recapitulate the human MPNs and provide powerful preclinical models to decipher the molecular bases of the differences between del[52] and ins[5] diseases
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
