a, b HELLS protein level in mouse (a) P21 retinae and (b) retinoblastoma tumor samples were compared with littermates’ controls (wt). Tubulin was used as a loading control. c Chromatin immunoprecipitation (ChIP) assay in P0 and P21 Rb1/p107 DKO mouse retinae and Weri retinoblastoma human cell line reveals enrichment of E2F1 within the HELLS promoter. IgG pull-down was used as negative control. d, e Western blot analysis of HELLS protein level at different retinal development stages in Rb1 cKO mice and Rb1/p107 DKO. Tubulin was used as a loading control. f Quantification of HELLS protein expression in Rb1/p107 DKO (black line) compared to wt (gray) retinae. g RT-qPCR analysis of Hells mRNA level in Rb1/p107 DKO retinae relative to E17.5 wild-type (wt) retinae. h Representative sequencing tracks for the Hells locus show increased peaks at the promoter in P21 Rb1/p107 DKO mouse retinal cells (EGFP+) compared with control retinal cells (EGFP−). The ATAC-Seq data have been normalized to take sequencing depth into account. All measurements are mean ± SD (n = 3).