RB1 and neoplasm: Since HELLS expression levels during the early stages of retinal development (E17.5 through P2) in Rb1/p107 DKO retinae are comparable with those observed in wild-type retinae, it is likely that the RB family is required for Hells repression during terminal differentiation of one or several retinal cell fates and failure to do so results in the aiding of tumor progression.