PRRX1 and osteoporosis: To test the hypothesis that Slc7a7 deficiency in mature osteoblasts or mesenchymal cells of the osteo-chondroprogenitor lineage hinders growth and skeletal development and leads to osteoporosis in vivo, we generated a conditional Slc7a7 mouse model and deleted Slc7a7 in the mature osteoblasts using the Ocn-Cre and in the osteo-chondroprogenitor cells using Prx1-Cre (Figs S8-S15).