POSITIONAL INFORMATION REGULATION DURING LEG DEVELOPMENT THROUGH FGF AND WNT SIGNALING

脊椎动物的肢体和无脊椎动物的附属物是通过对相应的发育区域进行细分而形成的，这些区域的形成受不同形态信号的浓度梯度控制，如Wnt和FGF。每个亚域可能具有自己独特的属性，如局部细胞粘附性的特异性，可能由转录因子的组合区域特异性表达所特异性。我们分离并鉴定了一些编码与果蝇腿和其他器官发育有关的形态原受体和转录因子的新基因。在这里，由于篇幅有限，我们只描述以下两个基因的性质。我们首次鉴定了DFrizzled3基因是编码果蝇Frizzled家族第三个成员的基因。与卷曲和卷曲-2不同，DFrizzled-3基因在转录水平上受到无翼信号的上调。虽然DFrizzled3蛋白在体外能够与无翼结合，但无翼依赖的手臂…转染腺病毒/β-连环蛋白的果蝇细胞中，腺病毒/β-连环蛋白的稳定化效果比转染组低得多。缺乏DFrizzled3活性的果蝇是存活和可繁殖的，几乎没有形态缺陷。遗传学和免疫学分析表明，DFrizzled3活性的缺失抑制了亚型无翼突变的影响，如翅膀和天线的形成失败，并在不改变无翼表达的情况下将靶基因表达恢复到正常水平。在果蝇腿的发育过程中，最远端的隔室(前膝部)和它的近端(第5节)分别由前膝部特异的同源异型盒基因、干旱性同源盒基因和鞑靼节段特异的Bar同源盒基因所特异性；前膝盖骨/鞑靼节段的边界是由Bar和包括干燥性在内的前膝盖骨特异基因之间的拮抗作用形成的。在这方面，我们发现果蝇LIM-1是脊椎动物LIM-1编码LIM同源结构域蛋白的同源物，它通过激活干旱参与了膝前区的指定和边界的形成。Lim1的异位表达导致了旱性误表达，而在Lim1缺失的突变克隆中，旱性显著降低。在缺乏干燥性活动的小腿间盘中，P抑制因子Lim1的表达受到Bar的负调控，并被取消，这与假定的膝前肌中强的Bar错误表达有关。无干旱误表达时，未出现Lim1错误表达。LIM1和ALASTESS的协同作用需要维持Fasciclin 2在边缘细胞中的表达，并形成平滑的眼睑前/睑骨节段边界。LIM1也是股骨、髋部和触角发育所必需的。较少

Vertebrate limbs and invertebrate appendages are formed through subdivision of the corresponding developing field, whose formation is governed by concentration garadients of various morphogen signals such as Wnt and FGF.Each subdomain, possibly with its own particular properties such as specificity in local cell adhesivity, may be specificed by a combinatorial region-specific expression of transcription factors. We isolated and characterized some new genes encoding morphogen receptors and transcriptional factors involved in the development of Drosophila legs and other organs. Here, we describe only the properties of the following two genes because of the limitation of space.We first identified Dfrizzled-3 as a gene encoding the third member of the Drosophila Frizzled family. In contrast to frizzled and frizzled-2, the Dfrizzled-3 gene was transcriptionally upregulated by Wingless signaling. Although Dfrizzled-3 protein was capable of binding to Wingless in vitro, Wingless-dependent Arm … More adillo/beta-catenin stabilization occurred much less effectively on Drosophila cells transfected with Dfrizzled-3 than those with Dfrizzled-2. Flies lacking Dfrizzled-3 activity were viable and fertile, with few morphological defects. Genetic and immunological analysis indicated that the absence of Dfrizzled-3 activity suppresses the effects of hypomorphic wingless mutations such as failure of wing and antenna formation and restores target gene expression to the normal levels without change in wingless expression. Wingless signaling may thus be attenuated by Dfrizzled-3 at least in wingless hypomorphic mutants.During Drosophila leg development, the distal-most compartment (pretarsus) and its immediate meighbour (tarsal segment 5) are specificied by a pretarsus-specific homeobox gene, aristaless, and tarsal-segment-specific Bar homeoboxes, respectively ; the pretarsus/tarsal segment boundary is formed by antagonistic interactions between Bar and pretarsus-specific genes that include aristaless. In this connection, we identified Drosophila Lim-1, a homologue of vertebrate Lim1 encoding a LIM-homeodomain protein, is involved in pretarsus specification and boundary formation through its activation of aristaless. Ectopic expression of Lim1 caused aristaless misexpression, while aristaless was significantly reduced in Lim1-null mutant clones. Pretarsus Lim1 expression was negatively regulated by Bar and abolished in leg discs lacking aristaless activity, which was associated with strong Bar misexpression in the presumptive pretarsus. No Lim1 misexpression occurred upon aristaless misexpression. The concerted function of Lim1 and aristaless was required to maintain Fasciclin 2 expression in border cells and form a smooth pretarsus/tarsal segment boundary. Lim1 was also required for femur, coxa and antennal development. Less