Figure 9

Model for osteoblast lineage development mediated by the Axin2/β-catenin/cyclin D1 regulatory pathway. Growing evidence suggests that Axin2/β-catenin regulates the self renewal of mesenchymal stem cells (MSCs) and the expansion of skeletogenic progenitors during calvarial morphogenesis [6–8]. This study shows that cyclin D1 is a downstream modulator, acting in this regulatory axis. Furthermore, canonical Wnt signaling promotes specification of osteoprogenitors which are Runx2+ and Osx+, but prohibits terminal differentiation of mature osteoblasts expressing high levels of Op. Nonetheless, osteoblasts expressing low levels of Op are matrix-secreting cells capable of mediating bone synthesis.