SIX1 and retinoblastoma: Co-electroporation of Six1 siRNAs with the mutated six1 mRNA reversed the knockdown effect of siRNAs (50.2 ± 3.6 cells, n = 22, p = 0.000001) (Figure 2N), confirming that the knockdown of Six1 itself causes a delay in the reduction of the number of RB cells.