Role of Cyp26b1 in endochondral bone formation

视黄酸（Retinoic acid， RA）在胚胎发育中起重要作用。降解RA的CYP26酶具有特定的表达模式并产生RA梯度。RA梯度调节胚胎中各种结构的模式。然而，尚不清楚RA梯度是否也存在于出生后的器官中。我们在幼年小鼠的生长板中发现了局部的RA活性。Cyp26b1在生长板软骨的增殖软骨细胞中特异性表达。软骨细胞特异性缺乏Cyp26b1 （Cyp26b1 cKO）的小鼠在幼年期表现出骨生长迟缓。生长板软骨增生软骨细胞增殖率下降。给Cyp26b1 cKO小鼠喂食缺乏维生素a的饮食可以部分逆转这些异常。这些结果表明，RA在生长板内的分布与幼体生长板和骨骼的正常功能有关。

Retinoic acid (RA) plays important roles in embryonic development. CYP26 enzymes, which degrade RA, have specific expression patterns and produce a RA gradient. RA gradient regulates the patterning of the various structures in embryos. However, it has not been addressed whether a RA gradient also exists in organs after birth.We found localized RA activities within the growth plate in juvenile mice. Cyp26b1 was specifically expressed in proliferative chondrocytes of the growth plate cartilage. The mice lacking Cyp26b1 specifically in chondrocytes (Cyp26b1 cKO) showed retardation of bone growth in the juvenile stage. Their growth plate cartilage showed decreased proliferation rates of proliferative chondrocytes. Feeding the Cyp26b1 cKO mice a vitamin A-deficient diet partially reversed these abnormalities. These results suggest that the RA distribution within the growth plate is responsible for the normal function of the growth plate and growing bones in juveniles.