Fig. 6. Loss of INK4b expression in immortalised chicken cells. (A) Polyadenylated RNA from the DT40 and DF1 cell lines, and from primary CEFs at 43 PDs, were hybridised with probes specific for INK4b and ARF as in Fig. 2. (B) DF1 cells were treated with 1 µM 5'-aza 2'-deoxycytidine (5'-aza C) for 4 days and assayed for expression of INK4b and ARF by semi-quantitative RT-PCR. Control CEF cells (PD 49) were exposed to solvent alone. GAPDH was used as loading control. The respective product sizes are 799 bp (INK4b), 592 bp (ARF) and 709 bp (GAPDH).