Generation of a conditional Flpo/FRT mouse model expressing constitutively active TGFβ in fibroblasts

Transforming growth factor (TGF beta) is a secreted factor, which accumulates in tissues during many physio- and pathological processes such as embryonic development, wound healing, fibrosis and cancer. In order to analyze the effects of increased microenvironmental TGF beta concentration in vivo, we developed a conditional transgenic mouse model (Flpo/Frt system) expressing bioactive TGF beta in fibroblasts, a cell population present in the microenvironment of almost all tissues. To achieve this, we created the genetically-engineered [Fsp1-Flpo; (FSF)TGF beta(CA)] mouse model. The Fsp1-Flpo allele consists in the Flpo recombinase under the control of the Fsp1 (fibroblast-specific promoter 1) promoter. The (FSF)TGF beta(CA) allele consists in a transgene encoding a constitutively active mutant form of TGF beta (TGF beta(CA)) under the control of a Frt-STOP-Frt (FSF) cassette. The (FSF)TGF beta(CA) allele was created to generate this model, and functionally validated by in vitro, ex vivo and in vivo techniques. [Fsp1-Flpo; (FSF)TGF beta(CA)] animals do not present any obvious phenotype despite the correct expression of TGF beta(CA) transgene in fibroblasts. This [Fsp1-Flpo; (FSF)TGF beta(CA)] model is highly pertinent for future studies on the effect of increased microenvironmental bioactive TGF beta concentrations in mice bearing Cre-dependent genetic alterations in other compartments (epithelial or immune compartments for instance). These dual recombinase system (DRS) approaches will enable scientists to study uncoupled spatiotemporal regulation of different genetic alterations within the same mouse, thus better replicating the complexity of human diseases.