Vale-Cruz Dustin S, Ma Qin, Syme Janet, LuValle Phyllis A
Interdisciplinary Program in Biomedical Sciences, Molecular Cell Biology Concentration, College of Medicine, University of Florida, Gainesville, FL 32610, USA.
Mech Dev. 2008 Sep-Oct;125(9-10):843-56. doi: 10.1016/j.mod.2008.06.010. Epub 2008 Jun 28.
Endochondral ossification is the process of skeletal bone growth via the formation of a cartilage template that subsequently undergoes mineralization to form trabecular bone. Genetic mutations affecting the proliferation or differentiation of chondrocytes result in skeletal abnormalities. Activating transcription factor-2 (ATF-2) modulates expression of cell cycle regulatory genes in chondrocytes, and mutation of ATF-2 results in a dwarfed phenotype. Here we investigate the regulatory role that ATF-2 plays in expression of the pocket proteins, cell cycle regulators important in cellular proliferation and differentiation. The spatial and temporal pattern of pocket protein expression was identified in wild type and mutant growth plates. Expression of retinoblastoma (pRb) mRNA and protein were decreased in ATF-2 mutant primary chondrocytes. pRb mRNA expression was coordinated with chondrogenic differentiation and cell cycle exit in ATDC5 cells. Type X collagen immunohistochemistry was performed to visualize a delay in differentiation in response to loss of ATF-2 signaling. Chondrocyte proliferation was also affected by loss of ATF-2. These studies suggest pRb plays a role in chondrocyte proliferation, differentiation and growth plate development by modulating cell cycle progression. ATF-2 regulates expression of pRb within the developing growth plate, contributing to the skeletal phenotype of ATF-2 mutant mice through the regulation of chondrocyte proliferation and differentiation.
软骨内成骨是通过形成软骨模板进行骨骼生长的过程，该软骨模板随后矿化形成小梁骨。影响软骨细胞增殖或分化的基因突变会导致骨骼异常。激活转录因子2（ATF-2）调节软骨细胞中细胞周期调节基因的表达，ATF-2突变会导致侏儒表型。在这里，我们研究ATF-2在口袋蛋白表达中所起的调节作用，口袋蛋白是细胞增殖和分化中重要的细胞周期调节因子。在野生型和突变型生长板中确定了口袋蛋白表达的时空模式。在ATF-2突变的原代软骨细胞中，视网膜母细胞瘤（pRb）mRNA和蛋白的表达降低。在ATDC5细胞中，pRb mRNA表达与软骨形成分化和细胞周期退出相协调。进行X型胶原免疫组织化学以观察到由于ATF-2信号缺失而导致的分化延迟。ATF-2的缺失也影响软骨细胞增殖。这些研究表明，pRb通过调节细胞周期进程在软骨细胞增殖、分化和生长板发育中发挥作用。ATF-2调节发育中的生长板内pRb的表达，通过调节软骨细胞增殖和分化，导致ATF-2突变小鼠出现骨骼表型。
