RNA expression data of embryonic E16.5 mouse temporomandibular joint (TMJ). Mus musculus

We conducted a genetic analysis of the developing temporo-mandibular joint (TMJ), a highly specialized synovial joint that permits movement and function of the mammalian jaw. First, we used laser capture microdissection to perform a genome-wide expression analysis of each of its developing components. The expression patterns of genes identified in this screen were examined in the TMJ and compared to other synovial joints including the shoulder joint and the hip joint. Striking differences were noted, indicating that the TMJ forms via a distinct molecular program. Several components of the Hedgehog (Hh) signaling pathway are among the genes identified in the screen, including Gli2, which is expressed specifically in the condyle and in the disk of the developing TMJ. We found that mice deficient in Gli2 display aberrant TMJ development such that the condyle loses its growth plate-like cellular organization and no disk is formed. In addition, we utilized a conditional strategy to remove activity of the Hh co-receptor encoded by Smo from chondrocyte progenitors. This cell autonomous loss of Hh signaling allows for disk formation, but the resulting structure fails to separate from the condyle. Thus, these experiments establish that Hh signaling acts at two distinct steps in disk morphogenesis, condyle initiation and disk-condyle separation, and provide a molecular framework for future studies of the TMJ. Overall design: Mouse embryos fresh frozen and TMJ tissue captured by LCM. 3 samples in biological triplicate.

本研究针对发育中的颞下颌关节（temporo-mandibular joint, TMJ）开展遗传学分析——该结构是一类高度特化的滑膜关节，负责介导哺乳动物下颌的运动与功能。首先，我们采用激光捕获显微切割（laser capture microdissection）技术，对该关节各发育组分开展全基因组表达分析。随后，我们对本次筛选中鉴定得到的基因在颞下颌关节中的表达模式进行检测，并与其他滑膜关节（包括肩关节与髋关节）的表达模式进行对比。结果显示二者存在显著差异，表明颞下颌关节的形成依赖一套独特的分子程序。本次筛选鉴定出的基因中包含多个刺猬信号通路（Hedgehog, Hh）组分，其中Gli2基因特异性表达于发育中颞下颌关节的髁突与关节盘内。我们发现，Gli2基因缺陷小鼠会出现颞下颌关节发育异常：髁突丧失其生长板样细胞组织结构，且无法形成关节盘。此外，我们利用条件性实验策略，去除软骨细胞祖细胞中由Smo基因编码的Hh信号共受体活性。该细胞自主性的Hh信号缺失虽可允许关节盘形成，但最终形成的结构无法与髁突分离。综上，上述实验证实Hh信号通路在关节盘形态发生的两个不同阶段发挥作用——髁突起始形成与关节盘-髁突分离，并为未来颞下颌关节的相关研究提供了分子框架。整体实验设计：将小鼠胚胎新鲜冷冻后，通过激光捕获显微切割获取颞下颌关节组织，实验设置3份生物学重复样本。