SP7 and osteosarcoma: Consistent with our published data in MEFs [18], primary cilia frequency in murine OS cell lines correlated to Hh responsiveness with non-responsive 45Ca cell lines exhibiting few or a complete absence of cilia, even after serum starvation, whilst all Osx p53Rb KO osteosarcoma cell lines were highly ciliated under serum free conditions and also displayed abundant cilia in normal serum conditions (Fig. 1d, e).