The PDGFRα(S)J conditional knockin allele has the endogenous PDGFRα sequences replaced with a loxP-flanked PGKneo (lox-stop-lox) cassette upstream of the constitutively active PDGFRαJ mutant isoform. This V561D mutation in the juxtamembrane domain disrupts inhibitory contacts between the juxtamembrane and kinase domains, which are important for full auto-inhibition, and results in constitutive PDGFRα activity. Prior to Cre recombinase exposure, no expression of the constitutively active αJ mutant isoform is observed, and the mutant allele functions as a knockout. Mice homozygous for the PDGFRα(S)J allele die during embryonic development. Heterozygous PDGFRα(S)J mice are viable and fertile with no reported abnormalities. Following Cre recombinase-mediated excision of the floxed-STOP cassette, high basal kinase activity without the addition of ligand is observed in the cre-expressing tissues.
Of note, pan-deletion of the floxed-STOP cassette during development can be achieved by breeding PDGFRα(S)J conditional knockin mice with Meox2Cre mice expressing Cre recombinase in the early embryo (Stock No. 003755). Alternatively, widespread deletion of the floxed-STOP cassette in adult mice can be achieved by breeding PDGFRα(S)J conditional knockin mice with ROSA26CreER mice ubiquitously expressing a tamoxifen-inducible Cre recombinase (Stock No. 004847). Following tamoxifen treatment in the double mutant embryos/animals, widespread expression of the constitutively active PDGFRαJ leads to connective tissue hyperplasia in embryos and widespread organ fibrosis in adult mice (resembling human autoimmune disease systemic sclerosis). Organs affected are intestine (w polyps), skin, heart, skeletal muscle, kidney glomeruli and renal insterstitium. Vascular smooth muscle is not affected. When comparing widespread Cre recombinase-activated phenotypes of PDGFRαJ to PDGFRαK (see Stock No. 018433), PDGFRαJ expression results in a more attenuated fibrotic disease than PDGFRαK.
