As expected, we observed that mouse Ppp2r1a−/− intestine tumours displayed high mutation burden (Fig. 2a), MMR-deficient signatures (Fig. 2b), COSMIC signatures associated with defective MMR (Fig. 2c), positive MSI assay results (Fig. 2d), downregulated MMR-associated genes (Fig. 2e), and reduced MLH1 protein levels in Ppp2r1a−/− intestine tumour organoid cultures (Fig. 2f, g) and primary tumour tissues (Fig. 2h). Here, MRC1 is linked to neoplasm.