A twist code determines the onset of osteoblast differentiation.
Runx2 is necessary and sufficient for osteoblast differentiation, yet its expression precedes the appearance of osteoblasts by 4 days. Here we show that Twist proteins transiently inhibit Runx2 function during skeletogenesis. Twist-1 and -2 are expressed in Runx2-expressing cells throughout the skeleton early during development, and osteoblast-specific gene expression occurs only after their expression decreases. Double heterozygotes for Twist-1 and Runx2 deletion have none of the skull abnormalities observed in Runx2(+/-) mice, a Twist-2 null background rescues the clavicle phenotype of Runx2(+/-) mice, and Twist-1 or -2 deficiency leads to premature osteoblast differentiation. Furthermore, Twist-1 overexpression inhibits osteoblast differentiation without affecting Runx2 expression. Twist proteins' antiosteogenic function is mediated by a novel domain, the Twist box, which interacts with the Runx2 DNA binding domain to inhibit its function. In vivo mutagenesis confirms the antiosteogenic function of the Twist box. Thus, relief of inhibition by Twist proteins is a mandatory event precluding osteoblast differentiation.
Bialek
Peter
P
Department of Molecular and Human Genetics, Bone Disease Program of Texas, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
Kern
Britt
B
Yang
Xiangli
X
Schrock
Marijke
M
Sosic
Drazen
D
Hong
Nancy
N
Wu
Hua
H
Yu
Kai
K
Ornitz
David M
DM
Olson
Eric N
EN
Justice
Monica J
MJ
Karsenty
Gerard
G
D000375:Aging / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D015152:Blotting, Northern / Q000379:methods; D015153:Blotting, Western / Q000379:methods; D002454:Cell Differentiation / Q000502:physiology*; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D050659:Core Binding Factor Alpha 1 Subunit; D004252:DNA Mutational Analysis / Q000379:methods; D024202:Electrophoretic Mobility Shift Assay / Q000379:methods; D004622:Embryo, Mammalian; D005786:Gene Expression Regulation / Q000502:physiology; D006579:Heterozygote; D017403:In Situ Hybridization; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D018006:Myogenic Regulatory Factors / Q000235:genetics / Q000502:physiology*; D009363:Neoplasm Proteins / Q000378:metabolism; D009687:Nuclear Proteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D010006:Osteoblasts / Q000502:physiology*; D010012:Osteogenesis / Q000502:physiology*; D011233:Precipitin Tests / Q000379:methods; D011392:Proline / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000502:physiology; D012313:RNA / Q000032:analysis; D051381:Rats; D012097:Repressor Proteins / Q000235:genetics / Q000502:physiology*; D012694:Serine / Q000235:genetics; D012863:Skeleton; D013194:Staining and Labeling; D014157:Transcription Factors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015533:Transcriptional Activation / Q000502:physiology; D014162:Transfection / Q000379:methods; D051879:Twist-Related Protein 1
D050659:Core Binding Factor Alpha 1 Subunit; D018006:Myogenic Regulatory Factors; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D051879:Twist-Related Protein 1; C096852:Twist2 protein, mouse; C067250:Twist1 protein, mouse; D012694:Serine; D012313:RNA; D011392:Proline