PCNA and retinoblastoma: In the SO-Rb50 retinoblastoma cell line, the mRNA levels of cdc25A, CDK2, PCNA and CDK1 were significantly higher in the PAX6 inhibition study group than in negative GFP-control group (cdc25A, 2.93±0.16 vs. 1.00±0.00; t=−21.47; P<0.01, n=3; CDK2, 1.75±0.11 vs. 1.00±0.00; t=−11.56; P<0.01, n=3; PCNA, 3.16±0.35 vs. 1.00±0.00; t=−10.86; P<0.01, n=3; CDK1, 2.11±0.21 vs. 1.00±0.00; t=−9.22; P<0.05, n=3) (Fig. 6A).