library_construction_protocol: Five mice were sacrificed by cervical vertebra dislocation and bladder was removed. The bladder was incubated in dispase II solution (04942078001, Sigma) at 37°C for 1.5 hours. The bladder was then enlarged to achieve a maximum stretch (Supplement Figure 1E). After dispase II solution was discarded, 10-15ml PBS-EDTA (10mmol/L, CZ0026, Leagene) was added to Sylgard-coated plate and shaking for 1.5 hours. The PBS-EDTA was collected and centrifuge at 300g for 5 minutes. The supernatant was aspirated and the cells were then digested in 1ml TrypLE™ Express Enzyme (12604-013, Thermo Fisher Scientific) for 1min. 10ml 0.04% BSA D-PBS solution (D1040, Solarbio) was added to stop the digestion and then centrifuge at 300g for 5 minutes. Cells were then resuspended in 10ml 0.04% BSA D-PBS solution and were sequentially filtered through 70 and 40 μm filters. Single-cell RNA-seq libraries were prepared with Chromium Single cell 3' Reagent v3) Kits according to the manufacturer's protocol. Single-cell suspensions were loaded on the Chromium Single Cell Controller Instrument (10×Genomics) to generate single cell gel beads in emulsions (GEMs).