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edited the manuscript. Reprints and permissions information is available online athttp://npg.nature.com/reprintsandpermissions/ == Recommendations == == Associated Data == This section collects any data citations, data availability statements, or supplementary materials included in this article. == Supplementary Materials ==. reduction in ectopic ossification and functional impairment. In contrast to localized induction of caALK2 by Ad.Cre (which entails inflammation), global postnatal expression of caALK2 (induced without the use of Ad.Cre and thus without inflammation) does not lead to ectopic ossification. However, if in this context an inflammatory stimulus was provided with a control adenovirus, ectopic bone formation was induced. Like LDN-193189, corticosteroid treatment inhibits ossification in Ad.Cre-injected mutant mice, suggesting caALK2 expression and an inflammatory milieu are both required for the development of ectopic ossification in this model. These results support the role of dysregulated ALK2 kinase activity in the pathogenesis of FOP and suggest that small molecule inhibition of BMP OC 000459 type I receptor activity may be useful in treating FOP and heterotopic ossification syndromes associated with excessive BMP signaling. Individuals with FOP typically present within the first decade of life with progressive ectopic calcification of muscles and connective tissues after physical trauma, surgery, viral illness or myositis14. FOP results in severe debilitation and reduced life expectancy due to joint fusion and restrictive lung disease with thoracic involvement. A recent linkage and sequencing analysis identified heterozygous mutations inACVR1, the gene encoding the BMP type I receptor ALK2, in all affected members from seven families5,7. BMP ligands facilitate the phosphorylation and activation of BMP type I receptors (ALK2, ALK3 and ALK6) by BMP type II receptors (BMPRII, ActRIIA and ActRIIB). Activated BMP type I receptors phosphorylate BMP-responsive SMAD1, SMAD5 and SMAD8, which translocate to the nucleus to regulate the transcription of genes, including the Inhibitor of DNA binding (ID) gene family, with broad effects on growth and differentiation8. The classic FOP-associated ALK2 mutation, R206H, is usually predicted to disrupt an -helix in the glycine-serine OC 000459 regulatory domain name and alter local electrostatic potential to perturb intra- or intermolecular interactions required for kinase regulation5,9, rendering ALK2 constitutively active. Heterozygous mutations affecting the adjacent residue, Q207E, have been identified in phenotypic variant FOP10. The Q207E mutation and a well described man-made ALK2 mutation affecting the same residue, Q207D11, may exert similarly disruptive effects around the glycine-serine domain name structure and to cause constitutive activation of ALK2.In vivo, transfer of the gene encoding ALK2Q207Dbut not wild-type ALK2 induces chondrogenic differentiation in chick embryos and promotes endochondral bone growth in cortical allografts12,13, consistent with potent osteogenic effects of constitutively activating ALK2 mutations. To further explore the ability of constitutively active ALK2 to induce ectopic calcification, we took advantage of the availability of transgenic mice expressing an inducible ALK2Q207D(CAG-Z-EGFP-caALK2, or conditional caALK2). When the transgene is usually globally expressed during embryogenesis, mice are arrested at mid-gestation14, in contrast to individuals with FOP, who appear essentially normal at birth except for shortened great toes2. To circumvent the embryonic lethality of this transgene, we induced postnatal over-expression of ALK2Q207Din the left hindlimbs of mice with retro-popliteal injection of Ad.Cre (1 108plaque-forming models (PFU)) on postnatal day 7 (P7). High-frequency, Cre-mediated recombination was evident by P11, with loss of nuclear -galactosidase staining and gain of cytoplasmic GFP expression OC 000459 in myocytes, ligaments and vasculature only in the injected area (Fig. 1a). Mononuclear infiltrates and myofiber edema were apparent in the left gastrocnemius, soleus and hamstring muscles, consistent with myositis induced by intramuscular adenovirus injection15, whereas muscles of uninjected Nog limbs appeared normal (Fig. 1a). == Physique 1. == Mouse model of FOP. (a) Staining of muscle sections from Ad.Cre-injected conditional caALK2expressing (ALKQ207D) mice. The injection done at P7 induced recombination in myocytes of the left (L) gastrocnemius and soleus muscles at P11, as evidenced by loss of nuclear -galactosidase (-gal) staining and gain of GFP expression. Squares indicate areas of low magnification examined at higher magnification to the OC 000459 right. H&E staining discloses mononuclear cell infiltrates and myocyte edema in tissues undergoing recombination, but not in uninjected right (R) hindlimb muscles. (b) Left hindlimb postural abnormalities were observed grossly (left) at P30 in the Ad.Cre-injected left hindlimbs of conditional caALK2 mice, but not in Ad.Cre-injected wild-type mice. The X-ray image (right) shows Ad.Cre-induced ectopic calcifications involving the left gastrocnemius, soleus and hamstring muscles of conditional caALK2 mice at P30. (c) Three-dimensional reconstructed images from CT cross-sections of an Ad.Cre-injected, conditional caALK2expressing mouse on P30 showing intramuscular ectopic bone within the left gastrocnemius, soleus, tibialis and hamstring muscles (rendered in.