Core binding factor beta (Cbfβ) is essential for embryonic bone morphogenesis. 
Yet the mechanisms by which Cbfβ regulates chondrocyte proliferation and 
differentiation as well as postnatal cartilage and bone formation remain 
unclear. Hence, using paired-related homeobox transcription factor 1-Cre 
(Prx1-Cre) mice, mesenchymal stem cell-specific Cbfβ-deficient (Cbfβ(f/f) 
Prx1-Cre) mice were generated to study the role of Cbfβ in postnatal cartilage 
and bone development. These mutant mice survived to adulthood but exhibited 
severe sternum and limb malformations. Sternum ossification was largely delayed 
in the Cbfβ(f/f) Prx1-Cre mice and the xiphoid process was noncalcified and 
enlarged. In newborn and 7-day-old Cbfβ(f/f) Prx1-Cre mice, the resting zone was 
dramatically elongated, the proliferation zone and hypertrophic zone of the 
growth plates were drastically shortened and disorganized, and trabecular bone 
formation was reduced. Moreover, in 1-month-old Cbfβ(f/f) Prx1-Cre mice, the 
growth plates were severely deformed and trabecular bone was almost absent. In 
addition, Cbfβ deficiency impaired intramembranous bone formation both in vivo 
and in vitro. Interestingly, although the expression of Indian hedgehog (Ihh) 
was largely reduced, the expression of parathyroid hormone-related protein 
(PTHrP) receptor (PPR) was dramatically increased in the Cbfβ(f/f) Prx1-Cre 
growth plate, indicating that that Cbfβ deficiency disrupted the Ihh-PTHrP 
negative regulatory loop. Chromatin immunoprecipitation (ChIP) analysis and 
promoter luciferase assay demonstrated that the Runx/Cbfβ complex binds putative 
Runx-binding sites of the Ihh promoter regions, and also the Runx/Cbfβ complex 
directly upregulates Ihh expression at the transcriptional level. Consistently, 
the expressions of Ihh target genes, including CyclinD1, Ptc, and Pthlh, were 
downregulated in Cbfβ-deficient chondrocytes. Taken together, our study reveals 
not only that Cbfβ is essential for chondrocyte proliferation and 
differentiation for the growth and maintenance of the skeleton in postnatal 
mice, but also that it functions in upregulating Ihh expression to promoter 
chondrocyte proliferation and osteoblast differentiation, and inhibiting PPR 
expression to enhance chondrocyte differentiation.