Illuminating DNA replication during Drosophila development using TALE-lights

SummaryNew discoveries allow systematic engineering of DNA sequence recognition using the modular recognition units of the transcription activator-like effectors (TALEs) or the guide RNA of the CRISPRs. The engineered specificity offers the potential to guide a wide range of activities to particular sequences [1–3], and targeted nucleases cause directed mutagenesis [4–6]. Here we have tagged sequences using fluorescent fusions that we call TALE-lights, and have used these to follow replication of particular satellite sequences during a major embryonic transition in Drosophila. We show that replication-timing of individual sequences can be measured. As embryos develop, the cell cycle extends and the timing of replication of satellite sequences shifts to later times within the more prolonged S phase. Here we show that the compact foci of satellite sequences expand in conjunction with their replication and that a satellite sequence, 359-bp, shows a particularly marked shift to later replication in the cell cycle after the midblastula transition (MBT). This replication behavior suggests that developmental signals can separately influence the timing of different satellite sequences