library_construction_protocol: Brains from 5-day post-fertilization zebrafish larvae were dissected in cold Ringer's solution. Following washes in DPBS, tissue was dissociated using Accumax Cell Dissociation Solution at 37°C with periodic trituration using a fire-polished glass pipette. The resulting single-cell suspension was filtered through a 40 µm cell strainer and centrifuged. Viable cells were resuspended in 1x PBS + 0.04% BSA for library preparation. Single-cell suspensions with >70% viability were processed using the 10X Genomics Chromium Single Cell 3' v3 protocol to generate Gel Bead-in-Emulsion (GEM) libraries. Approximately 10,000 cells were targeted per sample. Reverse transcription and cDNA amplification were performed in GEMs, followed by library construction according to the manufacturer's instructions. Libraries were sequenced on the Illumina NextSeq 500 platform with a target of 50,000 reads per cell.