A DLG1-ARHGAP31-CDC42 axis regulates the Wnt response in intestinal stem cells

A central factor in maintenance of tissue integrity is the response of stem cells to variations in the levels of niche signals. In the gut, intestinal stem cells (ISCs) depend on Wnt ligands for self-renewal and proliferation. Transient increases in Wnt signaling promote regeneration after injury or in inflammatory bowel diseases, whereas constitutive activation of this pathway leads to colorectal cancer. Here, we report that Discs large 1 (Dlg1) is dispensable for polarity and cellular turnover during intestinal homeostasis; however, Dlg1 is required for ISC survival in the context of increased Wnt signaling. RNA sequencing (RNAseq) and genetic mouse models demonstrated that DLG1 regulates the cellular response to increased canonical Wnt signaling. This occurs via transcriptional regulation of Arhgap31, a GTPase-activating protein that deactivates CDC42, an effector of the non-canonical Wnt pathway. These findings reveal a DLG1-ARHGAP31-CDC42 axis that is essential for the ISC response to fluctuating niche Wnt signaling. Overall design: Identification of differentially expressed genes in Dlg1 conditional knock out intestinal stem cells compared to wildtype controls at two days and 14 days after tamoxifen injection.