APICAL ECTODERMAL RIDGE ACTIVITY AND JOINT FORMATION

项目1将侧重于以下两个基本过程的方面 肢体模式形成、AER定向生长和肢体图案化 中胚层和连续软骨骨骼的分割 通过联合形成的两个或多个独立的元素。许多. 和AER一样，AER的细胞也在不断地发生凋亡。 引导肢体生长和构图，表明程序化细胞 死亡可能在维持AER活性和 发信号。这一假设将通过使用AER来部分检验- MSX-2基因中特异的增强子元件靶向异位表达 Bcl2，一种有效的细胞凋亡抑制因子，特异性地作用于 转基因小鼠的肢体发育以确定AER是否定向 肢体的突起或图案被改变。MSX-2和BMPs是高度 在内质网中表达，并参与调控细胞凋亡 轻中胚层，提示MSX-2和BMPS可能处于调节状态 控制广泛的程序性细胞死亡的网络 持续发生在急诊室。研究它们在AER中的作用和 研究它们在细胞凋亡和AER特异性增强子中的可能作用 MSX-2基因中的元件将被用来指导 BMP或MSX-2的抑制剂对转基因小鼠AER的作用。这个 同源框基因Cux，果蝇Cut的鸡同源基因 基因，在幼虫的所有离散部位都高度表达。 发育中肢体的关节形成，BMP家族成员Gdf5也是如此 这已被证明在节理形成中起着重要作用。这个 假设Cux在调节脑血管紧张素转换酶的发生中起关键作用 在骨架元素之间生成关节的分割过程 以及可能的关系将会被调查 在这一过程中，Cux和GDF5之间的关系。关节形成的起始时间是 以分化的软骨细胞联合转化为特征的 表达大量的软骨-- 特征性II型胶原进入扁平致密排列的细胞 关节带间少表达或不表达II型胶原。 脊椎动物Cut同源物通常是转录抑制物， 抑制组织特异性基因在多个谱系中的表达。 因此，关于COX可能调节关节形成开始的假设 至少部分通过抑制II型胶原的表达 基因或其他软骨特异基因，从而促进软骨的形成 关节带间组织，将进行研究。

Project 1 will focus on aspects of two fundamental processes involved in limb pattern formation, AER-directed outgrowth and patterning of limb mesoderm, and the segmentation of continuous cartilaginous skeletal rudiments into two or more separate elements by joint formation. Many of the cells of the AER continuously undergo apoptosis as the AER is directing limb outgrowth and patterning, suggesting that programmed cell death may play an important role in maintenance of AER activity and signalling. This hypothesis will be tested in part by using an AER- specific enhancer element in the Msx-2 gene to target ectopic expression of Bcl-2, a potent inhibitor of apoptosis, specifically to the AER of the developing limbs of transgenic mice to determine if AER directed outgrowth or patterning of the limb is altered. Msx-2 and BMPs is highly expressed in the ER and have been implicated in regulating apoptosis in light mesoderm, suggesting that Msx-2 and BMPS may be in a regulatory network that controls the extensive programmed cell death that continuously occurs in the AER. To study their functions in the AER and examine their possible roles in apoptosis, and AER-specific enhancer element in the Msx-2 gene will be used to direct the expression of inhibitors of BMP or Msx-2 function to the AERs of transgenic mice. The homeobox-containing gene Cux, the chicken ortholog of the Drosophila Cut gene, is highly expressed at all of the discrete sites of incipient joint formation in the developing limb, as is Gdf5, a BMP family member which has been shown to lay an important role in joint formation. The hypothesis that Cux plays a crucial role in regulating the onset of the segmentation process that generates joints between the skeletal elements of the limb will be investigated, as will the possible relationship between Cux and GDF5 in the process. The onset of joint formation is characterized by the joint conversion of differentiating chondrocytes that express high amounts that express high amounts of cartilage- characteristic type II collagen into the flattened densely packed cells of the joint interzone which express little or no type II collagen. Vertebrate Cut homologs in general are transcriptional repressors that inhibit the expression of tissue specific genes in multiple lineages. Thus the hypotheses that Cox might regulate the onset of joint formation at lest in part by repressing the expression of the type II collagen gene or other cartilage specific genes, thus facilitating the formation of the joint interzone tissue, will be studied.