library_construction_protocol: E16.5 dataset. Twenty-four hours following electroporation, pregnant female was anaesthetized and sacrificed. Embryos from the pregnant mouse were harvested. Embryos were first separated based on electroporated plasmids, decapitated and the cortex was dissected out in 1X HBSS. JUNB: The GFP+ cortices were separated, and the electroporated region was dissected and frozen straight away in 2 ml Eppendorf tubes. Four cortices were collected per condition. On the day of the snRNA-seq, samples were first gently thawed on ice and resuspended in 100 ul of lysis buffer composed of: 10 mM Tris-HCl (pH 7.4), 10 mM NaCl, 3 mM MgCl2, 0.01% NP-40, 1% BSA and 1 mM DTT. After 5 minutes of lysis on ice, 1 mL of HBSS was added. The samples were then centrifuged at 500 g for 5 minutes. After removing supernatant, the pellet was resuspended in 1 mL washing buffer composed of: 10 mM Tris-HCl (pH 7.4), 10 mM NaCl, 3 mM MgCl2, 1% BSA, 1 mM DTT and 0.5 U/μl RNAase inhibitor. Then, using the P1000 pipette, the samples were pipetted up and down 10 times. The samples were then centrifuged again for 5 minutes at 500 g. Supernatant was removed, 1 mL of additional washing buffer was added, and the pellet was resuspended. At this point, no clumps were seen, and the samples were passed through a 30-μm filter before FANS. Hoechst was used as a positive nuclei marker and 25'000 events representing Hoechst+GFP+ nuclei were sorted directly into empty 1.5 mL Eppendorf-tubes using Beckman Coulter MoFlo Astrios. Exactly 42.8 μL of the sorted nuclei were loaded on the first step of the 10x Next GEM v3.1 reagent kit on the Chromium controller. IRF1/EGR1: The TagBFP2-NLS+ cortices were separated, and the electroporated region was dissected and processed for cell dissociation using the Miltenyi Neural dissociation kit as described previously 87. Single cell suspensions were then passed through a 70-μm filter before FACS. Only 20,000 BFP+ cells were sorted into separate tubes for either Control, IRF1, EGR1, or IRF1+EGR1. The FAC-sorted cells were centrifuged for 5 min at 300 g and all but 42.8 μL was removed from the tube before resuspending once more and loading on the Chip G for 10x capture with Next GEM v3.1 reagent kit on the 10x Chromium X controller. P0 dataset. Four days after electroporations and after birth of pups, four litter-mates per condition were sacrificed by decapitation and the cortex was dissected out of the head in cold 1x HBSS in less than 5 mins. The electroporated region was microdissected in a fresh petri dish containing 1x HBSS and transferred into an eppendorf tube. Dissociations were performed using the Neural Dissociation kit (130-092-628; Miltenyi) by treating the microdissected tissue with Enzyme mix 1 for 7mins and then Enzyme mix 2 for 3mins. Cells were washed in sorting buffer (1x PBS, 1% BSA and 0.5 U/μl SUPERase-In RNase inhibitor (AM2694; ThermoFisher Scientific)) twice at 4 C with 300 g. 16,000 for Control and 50,000 JUNB electroporated RFP+ cells were sorted into separate tubes containing sorting buffer. Sorted cell suspension was centrifuged again for 5 min at 4 C with 300 g and all but around 43.2 μL was removed. The cell suspension was resuspended gently and processed with 10X Genomics Chromium Single Cell 3' v3 reagent kit on the Chromium X controller. Gene expression libraries were constructed according to the manufacturer's guidelines (10x Genomics NextGEM v3.1 reagent kit). TrackerSeq libraries were constructed as previously described (Bandler et al. 2022).