Interestingly, new subpopulations of fibroblasts within C1 (C0C1, C2C1, C3C1, and C4C1) emerged in the adult, including fibroblasts expressing the vitamin K-dependent matrix protein Mgp, which has been linked to mechanotransduction and fibrosis in breast cancer (Foster et al, 2022) (Fig. 1J,K). Here, MGP is linked to breast cancer.