Rif1 prolongs the embryonic S phase at the Drosophila mid-blastula transition
(A) Cell cycle–regulated recruitment of Cdc7 to the nucleus during early interphase shown by time-lapse microscopy of Cdc7-GFP, His2Av-RFP during nuclear cycle 12 using a 100× objective. (B) Live imaging of Cdc7-GFP embryos during cycles 10–14 reveals dilution of nuclear Cdc7 over the pre-MBT divisions (S9 Movie). (C) Fixed Cdc7-depleted embryos stained for DNA and tubulin. Yellow arrow indicates a centrosome not associated with a DNA mass. Adjacent enlarged images display magnified views of abnormal mitotic structures. (D) Fixed rif1 mutant embryo after maternal RNAi against cdc7 stained for DNA and tubulin. Deletion of rif1 restores cell cycles and early development to Cdc7-depleted embryos. (E) Hatch rate of embryos laid from mothers either heterozygous or homozygous for a deletion of rif1 and expressing maternal RNAi against cdc7. The total number of embryos counted is indicated in parentheses. The temperature at which both the flies were reared and the hatch rate performed is indicated. Cdc7, cell division cycle 7; EGFP, enhanced green fluorescent protein; GFP, green fluorescent protein; His2Av, histone 2A variant; MBT, mid-blastula transition; mRFP, monomeric red fluorescent protein; RFP, red fluorescent protein; Rif1, Rap1 interacting protein 1; RNAi, RNA interference; shRNA, short hairpin RNA; UAS, upstream activating sequence.