title: Cbfb regulates bone development by stabilizing Runx family proteins.
abstract: Runx family proteins, Runx1, Runx2, and Runx3, play important roles in skeletal development. Runx2 is required for osteoblast differentiation and chondrocyte maturation, and haplodeficiency of RUNX2 causes cleidocranial dysplasia, which is characterized by open fontanelles and sutures and hypoplastic clavicles. Cbfb forms a heterodimer with Runx family proteins and enhances their DNA-binding capacity. Cbfb-deficient (Cbfb(-/-) ) mice die at midgestation because of the lack of fetal liver hematopoiesis. We previously reported that the partial rescue of hematopoiesis in Cbfb(-/-) mice revealed the requirement of Cbfb in skeletal development. However, the precise functions of Cbfb in skeletal development still remain to be clarified. We deleted Cbfb in mesenchymal cells giving rise to both chondrocyte and osteoblast lineages by mating Cbfb(fl/fl) mice with Dermo1 Cre knock-in mice. Cbfb(fl/fl/Cre) mice showed dwarfism, both intramembranous and endochondral ossifications were retarded, and chondrocyte maturation and proliferation and osteoblast differentiation were inhibited. The differentiation of chondrocytes and osteoblasts were severely inhibited in vitro, and the reporter activities of Ihh, Col10a1, and Bglap2 promoter constructs were reduced in Cbfb(fl/fl/Cre) chondrocytes or osteoblasts. The proteins of Runx1, Runx2, and Runx3 were reduced in the cartilaginous limb skeletons and calvariae of Cbfb(fl/fl/Cre) embryos compared with the respective protein in the respective tissue of Cbfb(fl/fl) embryos at E15.5, although the reduction of Runx2 protein in calvariae was much milder than that in cartilaginous limb skeletons. All of the Runx family proteins were severely reduced in Cbfb(fl/fl/Cre) primary osteoblasts, and Runx2 protein was less stable in Cbfb(fl/fl/Cre) osteoblasts than Cbfb(fl/fl) osteoblasts. These findings indicate that Cbfb is required for skeletal development by regulating chondrocyte differentiation and proliferation and osteoblast differentiation; that Cbfb plays an important role in the stabilization of Runx family proteins; and that Runx2 protein stability is less dependent on Cbfb in calvariae than in cartilaginous limb skeletons.
authors.affiliation: Department of Cell Biology, Unit of Basic Medical Sciences, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan.
authors.forename: Xin
authors.initials: X
authors.lastname: Qin
authors.forename: Qing
authors.initials: Q
authors.lastname: Jiang
authors.forename: Yuki
authors.initials: Y
authors.lastname: Matsuo
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Kawane
authors.forename: Hisato
authors.initials: H
authors.lastname: Komori
authors.forename: Takeshi
authors.initials: T
authors.lastname: Moriishi
authors.forename: Ichiro
authors.initials: I
authors.lastname: Taniuchi
authors.forename: Kosei
authors.initials: K
authors.lastname: Ito
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Kawai
authors.forename: Satoshi
authors.initials: S
authors.lastname: Rokutanda
authors.forename: Shinichi
authors.initials: S
authors.lastname: Izumi
authors.forename: Toshihisa
authors.initials: T
authors.lastname: Komori
mesh_terms: D000818:Animals; D001846:Bone Development / Q000502:physiology*; D002454:Cell Differentiation; D019902:Chondrocytes / Q000166:cytology; D050659:Core Binding Factor Alpha 1 Subunit / Q000502:physiology*; D050658:Core Binding Factor beta Subunit / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D010006:Osteoblasts / Q000166:cytology
chemical_list: C493693:Cbfb protein, mouse; D050659:Core Binding Factor Alpha 1 Subunit; D050658:Core Binding Factor beta Subunit; C493716:Runx2 protein, mouse
keywords: CBFB; CCD; ENDOCHONDRAL OSSIFICATION; INTRAMEMBRANOUS OSSIFICATION; RUNX2