Rif1 prolongs the embryonic S phase at the Drosophila mid-blastula transition
(A) Stills from time-lapse imaging of mCherry-PCNA during S phase 14 in WT (top) or rif1 mutant (bottom) embryos. Yellow arrows indicate late replication foci. The plot on the right displays the total duration of S phase 14 in WT and rif1 embryos (S1 Data). Each data point represents a distinct embryo. The duration of S phase was scored from real-time records of PCNA dynamics. (B) Stills from time-lapse imaging following the TALE-light probe for the 1.686 satellite (upper) and mCherry-PCNA to follow replication during S phase 14 in WT and rif1 embryos. Yellow arrows indicate the decompacted signal from the 1.686 TALE-light during the replication of the 1.686 repeat. (C) WT (top) or rif1 (bottom) embryos were injected with GFP-HP1a to visualize nuclei and filmed during cycle 14. Of the rif1 embryos, 6 out of 82 underwent an early mitosis 14 (S8 Movie). (D) Still frames from movies following mCherry-PCNA during S phase 13 in WT and rif1 embryos after either control or triple cyclin RNAi injection. Mitotic-cyclin knockdown arrests the cell cycle but extends S phase in WT but not rif1 embryos. GFP, green fluorescent protein; HP1a, heterochromatin protein 1a; MBT, mid-blastula transition; PCNA, proliferating cell nuclear antigen; Rif1, Rap1 interacting factor 1; RNAi, RNA interference; TALE, transcription activator-like effector; WT, wild-type.