Imbalanced p15 expression results in RPC competition. (A) Schematic of clonal analysis of single 12-hpf RPCs by combining cell transplantation and photoconversion. (B and C) Representative images (B) and quantification of clone size (C) of 72-hpf clones in different retinal environments. WT → WT (n = 34) and WT → p15⁺ (n = 33) represent WT RPCs in WT and p15⁺ retinae, respectively. p15⁺ → WT (n = 35) and p15⁺ → p15⁺ (n = 32) represent p15⁺ RPCs in WT and p15⁺ retinae, respectively. Schematic inserts in B show the mosaicism of traced RPCs (magenta) surrounded by environmental RPCs (gray). OPL, the outer plexiform layer; IPL, the inner plexiform layer. (D) Proportions of each retinal cell type of 72-hpf clones in WT → WT, p15⁺ → p15⁺, and WT → p15⁺ groups. (E) Proportions of major clone types derived from single 12-hpf p15⁺ RPCs in WT retinae. (F and G) Representative images (F) and quantification of clone size (G) of clones derived from single 12-hpf WT (n = 29, 17, 21, 16, 12) and p15⁺ (n = 24, 21, 21, 20, 16) RPCs at 24, 36, 48, 60, and 72 hpf. In F, the area of dashed white circles represents the optic vesicle (12 hpf); the dashed white lines represent the apical (up) and basal (down) surfaces of the retinae (24, 36, 48, and 60 hpf), the OPL (up) and the IPL (down) of the retinae (72 hpf). Data in C and G represent mean ± SEM. Scale bars, 10 µm.