Retinal progenitor cells are sensitive to deregulated proliferation after acute inactivation of Rb and p107. (A) To determine if retinal progenitor cells are sensitive to deregulated proliferation after acute Rb inactivation in a p107-deficient genetic background, we labeled Rb
-/- P0 or P3 retinas for 24 h with [3H]thy and then electroporated them with a Cre-venus-YFP plasmid. After 3 days in culture, the retinas were labeled for 1 h with BrdU and dissociated, and the YFP+ and YFP- cells were purified by FACS. (B-F) The cells were then analyzed by immunostaining, single-cell scoring and real-time PCR. (B, C) Colocalization of BrdU and [3H]thy demonstrated that most cells that continued to proliferate after Rb inactivation were retinal progenitor cells. (D) Real-time RT-PCR analysis confirmed that the proliferating cells expressed retinal progenitor cell markers. (E, F) Immunostaining and colocalization with [3H]thy further confirmed the retinal progenitor cell characteristics of these cells. Scale bars: B and E, 10 μm.