We used the α-Cre transgene to delete floxed Rb exon 19 at embryonic day (E) 10 in peripheral retina [2]. RbloxP/loxP;α-Cre mice were bred with strains lacking E2f1 or E2f2 in the germ line, or a strain carrying a floxed E2f3 allele [5]. RbloxP/loxP;E2f1+/− and RbloxP/loxP;E2f1+/−;α-Cre mice were bred to produce RbloxP/loxP;E2f1−/−;α-Cre mice at a frequency of 1/8 and littermate controls at the same or higher (1/4) frequency. For simplicity we will refer to the RbloxP/loxP;E2f1−/−;α-Cre peripheral retina as the Rb/E2f1 double knockout (DKO) retina. Similar strategies were employed in the case of E2f2 or E2f3. Cre-mediated excision of Rb and E2f3 alleles in the retina was confirmed by PCR as described previously [2,5].