library_construction_protocol: Tissue was dissected into sterile PBS. Cells were dissociated by incubation in TrypLE Express (Gibco 12605010) for 15 minutes at 37˚ C, gently pipetting with a siliconized wide bore pipette every 5 minutes. All steps after dissociation were performed on ice. Dissociated cells were filtered through a FlowMi Cell Strainer (Sigma BAH136800040), and centrifuged at 184 RCF for 2 minutes at 4˚ C.  Cells were resuspended in DMEM/20% FBS,  preparations from 3 littermates were then pooled at each timepoint, cells were centrifuged again as above and resuspended in DMEM/20% FBS. Cells were encapsulated and libraries produced using the using 10x Genomics Chromium method with the Chromium Single Cell 3' Reagent Kit (version 3.1).