Fig. 4. Apoptotic cells identified by Acridine Orange staining and TUNEL assay. Embryonic cells were injected with control-MO or PSR-MO (40 ng per embryo) at the one-cell stage to block translation of psr mRNA. (A-C,E) Acridine Orange staining of 17 hpf control-MO (A), 17 hpf PSR-MO (B), 14 hpf PSR-MO (C) and 17 hpf PSR-MO (E) embryos. (D) Phase-contrast image of the PSR-MO group at 17 hpf. (F-I) TUNEL assay at 12 hpf stage. (F,H) Phase-contrast images of control-MO (F) and PSR-MO (H) groups. (G,I) Observation of the embryos under a fluorescent microscope allows the identification of positive apoptotic cells in the PSR-MO group (I), when compared with the control-MO group (G). (D,E) Corpse cells released (see B) accumulate predominantly in the furrow between somites. AC, apoptotic cells; S, clear somites. Scale bars: 100 µM.