To determine if SYK might contribute to retinoblastoma initiation, dissociated fetal retinal cells were transduced with an RB1-directed shRNA (shRB1-733) known to induce cone precursor proliferation (Xu et al., 2014), treated with the selective SYK inhibitor GS-9876 (Blomgren et al., 2020) for 12 days, and examined for cone precursor cell cycle entry by co-staining for RXRγ and Ki67. Here, MKI67 is linked to retinoblastoma.