The ratio of RANKL to OPG is considered the main regulator of the bone remodelling process, and its imbalance can lead to the loss (osteoporosis) or gain (osteopetrosis) of bone density.14 Therefore, we quantitatively analysed the expression of RANKL and OPG in the sagittal suture and found that RANKL expression was significantly decreased in Gli1-CreERT2;Bmpr1afl/fl mice, although OPG expression appeared unaffected (Fig. 4f). Here, GLI1 is linked to osteopetrosis.