A versatile chondrogenic rat calvaria cell line R-tTA-24 that permits tetracycline-regulated gene expression.

The clonal rat calvaria cell line RCJ3.1C5.18 (RCJ) undergoes chondrogenic differentiation after long-term culture post confluence. To allow flexible genetic manipulation, a tetracycline-regulated gene expression system was established in this cell line. Treatment with tetracycline in operational doses does not affect the differentiation of RCJ cells with respect to the markers tested. After stable transfection with pUHD15.1 containing the tetracycline transactivator (tTA) in the presence of pTK-hyg for hygromycin selection, 28 clones were isolated and characterized for alcian blue staining of cartilage-specific proteoglycans and for collagen type II expression. Clone R-tTA-24 was selected on the basis of phenotype and displayed tetracycline-dependent down-regulation of luciferase activity (tet-OFF system) by two orders of magnitude (57-149-fold) after stable transfection with the reporter gene pBI-EGFP/luc. The novel, chondrogenic cell line R-tTA-24 may be stably transfected with various genes of interest for tetracycline-regulated gene expression using neomycin selection and may be a valuable tool to study the process of chondrogenic differentiation in vitro.