SMAD3 Reporter Mouse for Assessing TGF-ß/Activin Pathway Activation

The Transforming Growth Factor Beta (TGF-ß) ligands (i.e., TGF-ß1, -ß2, -ß3) are key regulatory proteins in animal physiology. Disruption of normal TGF-ß signaling is associated with many diseases from cancer to fibrosis. In mice and humans, TGF-ß activates TGF-ß receptors (e.g., TGFBR1), which activates SMAD proteins that alter gene expression and contribute to tumorigenesis.  Reliable animal models are essential for the study of TGF-ß signaling. A previously developed animal model for TGF-ß signaling utilizes a luciferase expression system under the control of SMAD protein responsive promoter elements (Lin et al., 2005, J. Immunol). The luciferase-based reporter mouse requires administering luciferin for bioluminescence detection. Another previously developed model is a SMAD protein-responsive, green fluorescent protein (GFP)-based reporter mouse (Neptune et al., 2003, Nat. Genet.); however, the model is no longer available. Thus, there remains a need for novel reporter animal models to study TGF-ß signaling.

NCI investigators designed an enhanced GFP (eGFP)-based reporter construct that is more sensitive to SMAD3 activation than other existing reporter constructs. Expression of eGFP is driven by an artificial enhancer element consisting of six repeats of a strong SMAD3 binding element. This reporter was greater than ten times more sensitive in vitro than the CAGA12-based reporter, another commonly used construct to detect TGF-ß signaling.  Using CRISPR/Cas9 technology, the inventors knocked this reporter construct into the Rosa26 locus, a ubiquitously expressed gene in most cells of the mouse. This strategy allows identification of tissues and cells in which signaling of TGF-βs are endogenously active during normal development, tissue homeostasis, and disease.

The mouse model is currently undergoing further validation using genetic and pharmacological approaches. It is available for licensing.