The concomitant expression of Dmp1 and full-length RANKL induced by RA in vitro is in agreement with our present and previous [19]in vivo observations of increased periosteal Dmp1 staining and the number of cathepsin K-positive osteoclasts in hypervitaminosis A. Although we have not been able to stain for full-length RANKL in these bone sections, it is tempting to speculate that vitamin A concomitantly induces Dmp1 and RANKL also in vivo, and that the full-length RANKL in these periosteal cells stimulates the formation of periosteal osteoclasts. Here, CTSK is linked to hypervitaminosis A.