FN1 and cyst: Given our ex vivo duct culture showed BEC-derived fibronectin promotes cyst expansion via SMAD3, we administered 6-month cyst-bearing Wdr35-/- animals the SMAD3 inhibitor SIS3 or vehicle alone for 3 weeks (Fig. 2F) to determine whether in vivo inhibition of SMAD3 signalling impacts the production of fibronectin and progression of cystogenesis.