p15 overexpression decreases RPC proliferation rate. (A) Representative images showing G1 RPCs (magenta) and S/G2/M RPCs (green) in the 24-hpf retina of Tg(zFucci). Areas within white dashed contour lines are the retinae. (B) The proportions of G1 cells (magenta) in total cells in the 24-hpf retinae of Tg(zFucci) with or without p15 overexpression. (C) Schematic procedure of time-lapse imaging to measure cell-cycle length of 12-hpf RPCs. (D) Representative cases showing the time-lapse tracing of single WT RPC (upper row) and single p15⁺ RPC (bottom row) from 12 hpf. The yellow arrowheads indicate the RPCs undergoing mitosis. The area of dashed white circles is the optic vesicle, and the area between two dashed white lines is the retina. (E) Frequency distribution of the cell-cycle length of individual 12-hpf WT RPCs (n = 25). (F) The proportion of 12-hpf p15⁺ RPCs with a cell-cycle length >12 h (n = 28). Scale bars, 10 µm.