Somatic mutations in the endoplasmic reticulum chaperone calreticulin (CALR) are detected in approximately 40% of patients with essential thrombocythemia (ET) and primary myelofibrosis (PMF). Multiple different mutations have been reported, but all result in a +1-bp frameshift and generate a novel protein C terminus. In this study, we generated a conditional mouse knockin model of the most common CALR mutation, a 52-bp deletion. The mutant novel human C-terminal sequence is integrated into the otherwise intact mouse CALR gene and results in mutant CALR expression under the control of the endogenous mouse locus. CALR mice develop a transplantable ET-like disease with marked thrombocytosis, which is associated with increased and morphologically abnormal megakaryocytes and increased numbers of phenotypically defined hematopoietic stem cells (HSCs). Homozygous CALR mice developed extreme thrombocytosis accompanied by features of MF, including leukocytosis, reduced hematocrit, splenomegaly, and increased bone marrow reticulin. CALR HSCs were more proliferative in vitro, but neither CALR nor CALR displayed a competitive transplantation advantage in primary or secondary recipient mice. These results demonstrate the consequences of heterozygous and homozygous CALR mutations and provide a powerful model for dissecting the pathogenesis of CALR-mutant ET and PMF.

Ten genes (ANK1, bR10D1, CA3, EPOR, HMGA2, MYPN, NME1, PDGFRA, ERC1, TTN), whose candidacy for meat-quality and carcass traits arises from their differential expression in prenatal muscle development, were examined for association in 1700 performance-tested fattening pigs of commercial purebred and crossbred herds of Duroc, Pietrain, Pietrain x (Landrace x Large White), Duroc x (Landrace x Large White) as well as in an experimental F(2) population based on a reciprocal cross of Duroc and Pietrain. Comparative sequencing revealed polymorphic sites segregating across commercial breeds. Genetic mapping results corresponded to pre-existing assignments to porcine chromosomes or current human-porcine comparative maps. Nine of these genes showed association with meat-quality and carcass traits at a nominal P-value of < or = 0.05; PDGFRA revealed no association reaching the P < or = 0.05 threshold. In particular, HMGA2, CA3, EPOR, NME1 and TTN were associated with meat colour, pH and conductivity of loin 24 h postmortem; CA3 and MYPN exhibited association with ham weight and lean content (FOM) respectively at P-values of < 0.003 that correspond to false discovery rates of < 0.05. However, none of the genes showed significant associations for a particular trait across all populations. The study revealed statistical-genetic evidence for association of the functional candidate genes with traits related to meat quality and muscle deposition. The polymorphisms detected are not likely causal, but markers were identified that are in linkage disequilibrium with causal genetic variation within particular populations.