Generation of stable HC11 cell lines expressing β-galactosidase and Δ Nβ-catenin in a tetracycline dependent manner. (a) HC11-lacZ cells – β-galactosidase activity of cell lysates following incubation for three days at the indicated tetracycline concentrations. β-galactosidase expression is effectively repressed at 20 ng/ml tetracycline. The assay was carried out in triplicate and results are presented as the mean β-galactosidase activity (normalised to the protein concentration of the samples) ± standard error. (b) Western blot of total cell lysates from HC11-ΔNβ-catenin cells cultured ± tetracycline. The N-terminal deletion mutant of β-catenin is detected by both its myc-epitope tag and the anti-β-catenin antibody. tTA was detected only in the absence of tetracycline, confirming the autoregulatory nature of the induction system.