Selection of MBF-F11 cells. Tgf-b1-/- mouse embryonic fibroblast clones that are stably transfected with SBE-SEAP (Clones 1 – 42) show induction of the reporter after treatment with 1 ng/ml TGF-β1 at passage 2 (A) and at passage 9–12 (B). Clone 43 is a control non-inducible clone. Assays were performed in 1 ml total volume and SEAP activity was measured in 10 μl supernatant after 24 h induction. The baseline measurement (no TGF-β) of each clone was used to calculate fold induction.