Bialek Peter, Kern Britt, Yang Xiangli, Schrock Marijke, Sosic Drazen, Hong Nancy, Wu Hua, Yu Kai, Ornitz David M, Olson Eric N, Justice Monica J, Karsenty Gerard
Department of Molecular and Human Genetics, Bone Disease Program of Texas, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
Dev Cell. 2004 Mar;6(3):423-35. doi: 10.1016/s1534-5807(04)00058-9.
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.
Runx2对于成骨细胞分化是必需且充分的，但其表达比成骨细胞的出现提前4天。我们在此表明，Twist蛋白在骨骼形成过程中短暂抑制Runx2功能。Twist-1和-2在发育早期整个骨骼中表达Runx2的细胞中表达，而成骨细胞特异性基因表达仅在它们的表达降低后才出现。Twist-1和Runx2缺失的双杂合子没有在Runx2(+/-)小鼠中观察到的颅骨异常，Twist-2基因敲除背景挽救了Runx2(+/-)小鼠的锁骨表型，并且Twist-1或-2缺陷导致成骨细胞过早分化。此外，Twist-1过表达抑制成骨细胞分化而不影响Runx2表达。Twist蛋白的抗成骨功能由一个新的结构域Twist框介导，该结构域与Runx2 DNA结合结构域相互作用以抑制其功能。体内诱变证实了Twist框的抗成骨功能。因此，Twist蛋白抑制作用的解除是排除成骨细胞分化的必要事件。
