Role of Dlx-5 in Chondrocyte Differentiation

软骨模型生成后形成肢体骨骼的软骨内骨化过程， 依赖于软骨细胞成熟的精心调节程序。基因和信号分子的鉴定 控制肥大软骨细胞成熟和它们之间的调节相互作用对于理解 骨骼生长和发育。本研究的目的是探讨同源域转录的假设， Dlx5因子是软骨内骨化过程中软骨细胞成熟的关键正调控因子， Dlx 5与控制过程中涉及的其他因素之间的关系。Dlx5在转换期间表示为 未成熟的增殖软骨细胞到有丝分裂后的前肥大软骨细胞，这是成熟的关键步骤。录病毒 在体内鸡肢骨骼成分分化过程中Dlx5的错误表达导致严重的 含有过量肥大软骨细胞的缩短的骨骼元件，扩展和上调的结构域 肥大分化的一些分子标志物的表达，包括骨桥蛋白和X型胶原， 矿化软骨基质扩张。Dlx5错误表达也显著降低细胞增殖，伴随着 促进肥大成熟。这些结果表明，Dlx5至少部分通过促进细胞的成熟来正向调节成熟。 未成熟增殖软骨细胞向肥大软骨细胞的转化。Dlx 5在软骨细胞中的作用 将通过检测鸡肢中Dlx 5错误表达对Dlx基因表达的影响来进一步研究成熟。 肥大成熟的其他标志物，并确定当Dlx 5 错误表达特异性靶向转基因小鼠胚胎四肢的软骨模型。还将 如果成熟由Dlx 6（Dlx家族的推定功能冗余成员）促进，则为d_终止。机制 将使用肢体间充质细胞中获得和丧失功能的方法来研究Dlx 5对成熟的调节。 和软骨细胞模型培养系统。可能的调节关系是：Dlx5和其他正调节因子之间的关系。 将研究软骨细胞成熟，包括RMP、Cbfal/Runx2和[ %连环蛋白介导的Wnt信号传导。各种 分子激动剂和拮抗剂将用于开始解开Dlx 5和其他因子如何相互作用和合作 在调节肥大性成熟中的作用。还将确定Dlx5是否参与转录调控。 骨桥蛋白、骨唾液酸蛋白和X型胶原基因在软骨细胞成熟过程中的作用。Dlx5与 并与BMP信号传导途径和/或Cbfal/Runx2在一个基因的启动子的转录调节中协作， 将研究这些候选靶基因中的一个或多个。

The process of endochondral ossification in which the bones of the limb are formed after generation of cartilage models is dependent on a carefully regulated program of chondrocyte maturation. Identification of the genes and signaling molecules that control hypertrophic chondrocyte maturation and the regulatory interactions among them is crucial to understanding bone growth and development. The goal of this research is to investigate the hypothesis that the homeodomain transcription factor Dlx5 is a key positive regulator of chondrocyte maturation during endochondral ossification, and to unravel the relationships between Dlx5 and other factors involved in controlling the process. Dlx5 is expressed during the conversion of immature proliferating chondrocytes to postmitotic prehypertrophic chondrocytes, a critical step in maturation. Retroviral misexpression of Dlx5 during differentiation of the skeletal elements of the chick limb in vivo results in formation of severely shortened skeletal elements that contain excess numbers of hypertrophying chondrocytes, expanded and upregulated domains of expression of some molecular markers of hypertrophic differentiation including osteopontin and type X collagen, and expansion of mineralized cartilage matrix. Dlx5 misexpression also markedly reduces cell proliferation concomitant with promoting hypertrophic maturation. These results suggest Dlx5 positively regulates maturation at least in part by promoting conversion of immature proliferating chondrocytes to hypertrophying chondrocytes. The role of Dlx5 in chondrocyte maturation will be further investigated by examining effects of Dlx5 misexpression in the chick limb on expression of additional markers of hypertrophic maturation, and determining if chondrocyte maturation is promoted when Dlx5 misexpression is specifically targeted to the cartilage models of the limbs of transgenic mouse embryos. It will also be d_termined if maturation is promoted by Dlx6, a putative functionally redundant member of the Dlx family. The mechanism of Dlx5 regulation of maturation will be investigated using gain- and loss-of-flmction approaches in limb mesenchymal cell and chondrocyte model culture systems. The possible regulatory relationships be:ween Dlx5 and other positive regulators of chondrocyte maturation including RMPs, Cbfal/Runx2, and [%catenin-mediated Wnt signaling will be investigated. A variety of molecular agonists and antagonists will be used to begin to unravel how Dlx5 and the other factors interact and cooperate in regulating hypertrophic maturation. It will also be determined if Dlx5 participates in transcriptional regulation of the osteopontin, bone sialoprotein, and type X collagen genes during chondrocyte maturation. The possibility that Dlx5 interacts and cooperates with the BMP signaling pathway and/or Cbfal/Runx2 in the transcriptional regulation of the promoters of one or more of these candidate target genes will be investigated.