X-ray-induced cell cycle arrest at G2/M-checkpoint in embryonic chick retina is abrogated at about 3 hours post-irradiation throughout development.

<p>(A-F) Staining against the mitotic marker pH3 (red) in control (A-C) and 2 Gy (D-F) irradiated E3 retinae at 1, 3 and 6 hrs after irradiation. Nuclei were counterstained with DAPI (blue). Note absence of mitotic cells up to 3 hrs after irradiation. (G) Mitotic index in retinae of E3 embryos after irradiation with various doses at different time points. (H) Absolute numbers of mitotic events in retinal slices of E5 after irradiation with various doses at different time points. (I) Absolute numbers of mitotic events in retinal slices of E7 after irradiation with various doses at different time points. Note that at all stages, cells are released from G2-arrest around 3 hrs after irradiation. Data are presented as means (n = 3, with at least 100 cell analyzed for E3 and at least three different retinal slices analyzed for E5 and E7) ± SEM. (*P<0.05 **P< 0.01 *** P<0.001). Scale bar = 25 μm. RPE, retinal pigmented epithelium; pONL, presumptive outer nuclear layer.