Protocols: Cell Sorting: tdRFP-positive mouse mammary epithelial cells (MMECs) were flow-sorted from 9-week-old female mice of the B-cat+/WT, B-cat+/R1KO, and B-cat+/DKO cohorts that had been crossed with a tdRFP reporter line. Flow-sorted cells from 3-6 individual mice of the same genotype were pooled together.  RNA extraction was performed using the RNAqueous™-Micro Total RNA Isolation Kit [Invitrogen], and the protocol provided by the manufacturer was followed. The protocol included a step to remove any residual genomic DNA using the DNA-free™ system. RNA-seq libraries were prepared using the SMARTer Stranded Total RNA-Seq Kit v2 - Pico Input Mammalian [Takara Bio]. Following preparation, the quality of the libraries was assessed using the Agilent 2200 TapeStation System with a High Sensitivity D1000 ScreenTape Analysis, and the quantity was measured using a Qubit Fluorometer.