Wild-type embryos from Canton S flies were laid on apple-agar plates in two-hour or four-hour windows, left to age for the specified time window, then collected from the plates, cleaned and dechorionated. Embryos were dissociated in ice-cold hypotonic lysis buffer with a Dounce homogenizer, filtered through a cell strainer, and nuclei were cross-linked on ice for 30 minutes.
