library_construction_protocol: Larval brains were dissected in PBS, and processed for DamID-seq as previously described (Marshall et al., 2016; Marshall and Brand, 2017) with the following modifications. Briefly, DNA was extracted using a Quick-DNA Miniprep plus kit (Zymo), digested with DpnI (NEB) overnight and cleaned-up with a PCR purification kit (Machery-Nagel), DamID adaptors were ligated, digested with DpnII (NEB) for 2 hours, and amplified via PCR using MyTaq DNA polymerase (Bioline). 2 µg DNA was sonicated in a Bioruptor Plus (Diagenode). DamID adaptors were removed by AlwI digestion, and 500 ng of the resulting fragments end-repaired with a mix of enzymes (T4 DNA ligase (NEB) + Klenow Fragment (NEB) + T4 polynucleotide kinase (NEB)), A-tailed with Klenow 3' to 5' exo- (NEB), ligated to Illumina Truseq LT adaptors using Quick Ligase enzyme (NEB) and amplified via PCR with NEBNext Hi-fidelity enzyme (NEB).