Different Requirements of CBFB and RUNX2 in Skeletal Development among Calvaria, Limbs, Vertebrae and Ribs.

RUNX proteins, such as RUNX2, regulate the proliferation and differentiation of chondrocytes and osteoblasts. Haploinsufficiency of causes cleidocranial dysplasia, but a detailed analysis of mice has not been reported. Furthermore, CBFB is required for the stability and DNA binding of RUNX family proteins. CBFB has two isoforms, and CBFB2 plays a major role in skeletal development. The calvaria, femurs, vertebrae and ribs in mice were analyzed after birth, and compared with those in mice. Calvarial development was impaired in mice but mildly delayed in mice. In femurs, the cortical bone but not trabecular bone was reduced in mice, whereas both the trabecular and cortical bone were reduced in mice. The trabecular bone in vertebrae increased in mice but not in mice. Rib development was impaired in mice but not in mice. These differences were likely caused by differences in the indispensability of CBFB and RUNX2, the balance of bone formation and resorption, or the number and maturation stage of osteoblasts. Thus, different amounts of CBFB and RUNX2 were required among the bone tissues for proper bone development and maintenance.