POSITIONAL INFORMATION REGULATION DURING LEG DEVELOPMENT THROUGH FGF AND WNT SIGNALING

脊椎动物肢体和无脊椎动物附属物是通过相应发育场的细分而形成的，其形成受各种形态因子信号如Wnt和FGF的浓度梯度控制。每个子结构域可能具有其自身的特性，如局部细胞粘附的特异性，可以通过转录因子的组合区域特异性表达来指定。我们分离并鉴定了一些新的基因编码形态发生受体和转录因子参与果蝇腿和其他器官的发育。这里，由于篇幅所限，我们只描述以下两个基因的性质。我们首先确定了dzzzzled3是果蝇frzzled3家族第三个成员的编码基因。与frizzed和frizzed -2相比，dfrizzed -3基因通过无翼信号表达上调转录。尽管dzzzzled3蛋白能够在体外与无翼细胞结合，但与无翼依赖性的Arm相比，dzzzzled3蛋白在果蝇细胞上的adillo/ β -catenin稳定效果要差得多。缺乏dzzzzr -3活性的蝇活育性好，形态缺陷少。遗传学和免疫学分析表明，dzzzzled3活性的缺失抑制了次形无翼突变（如机翼和天线形成失败）的影响，使靶基因的表达恢复到正常水平，而无翼表达没有变化。因此，至少在无翼半胚突变体中，无翼信号可能被dzzzzled3减弱。在果蝇的腿发育过程中，最远的隔室（跗前节）及其邻近的隔室（跗骨第5节）分别由跗前节特异性同源盒基因、无aristaless基因和跗骨节特异性Bar同源盒基因指定；跗骨前/跗骨节边界是由Bar和跗骨特异性基因之间的拮抗相互作用形成的。在这方面，我们发现果蝇Lim-1是脊椎动物Lim1的同源物，编码lim同源结构域蛋白，通过激活无aristaless参与前跗关节规范和边界形成。Lim1的异位表达导致无马兜铃错误表达，而在Lim1缺失的突变克隆中，无马兜铃显著减少。Lim1的表达受到Bar的负调控，在缺乏无马臀肌活动的腿椎间盘中被消除，这与假定的前跗骨中强烈的Bar错误表达有关。不存在Lim1错表达。为了维持Fasciclin 2在边界细胞中的表达并形成平滑的跗骨前/跗骨节边界，需要Lim1和aristaless的协同作用。股骨、髋和触角的发育也需要Lim1。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