Fig. 8. PTHrP signals block chondrocyte hypertrophy by both Nkx3.2/Bapx1-dependent and -independent pathways. Our findings indicate that PTHrP signals are necessary and sufficient to maintain the expression of Nkx3.2/Bapx1 in the proliferative region of the growth plate, and suggest that Nkx3.2/Bapx1 blocks chondrocyte maturation in this region of the growth plate by repressing the expression of Runx2 mRNA and possibly other co-factors necessary for chondrocyte hypertrophy. In addition, PTHrP signals can signal via a cAMP-dependent pathway to block the ability of Runx2 to induce chondrocyte maturation in a post-transcriptional manner.