GENETIC ANALYSIS OF EARLY LIMB DEVELOPMENT

该项目是一个研究项目的一部分，旨在通过小鼠突变和多态性定义的新基因的特征来了解正常和异常肢体模式形成的分子机制。脊椎动物胚胎肢体的生长和近端远端模式需要由顶端外胚层脊（AER）向进展区（PZ）发出信号，进展区在响应中增殖，并在近端到远端进展中奠定假设肢体的细胞。AER和PZ之间的信号环是维持肢体生长和模式的必要条件，在抗异形小鼠突变Dactylaplasia （Dac）中被破坏。Dac是按位置克隆的，发现它编码了一个先锋基因，其序列与功能无关。菌株多态性的抑制等位基因修饰子（Modifier of Dactylaplasia, Mdac）本身没有表型，但以100%的外显率显性抑制Dac。本研究有三个目的：(1)通过(a)产生和表征一个目标空等位基因来了解Dac基因的发育功能；(b)确定两个自发突变Dac1J和Dac2J发挥其优势作用的机制；(2)生成试剂（抗体和全长cDNA），以便将来对Dac基因的生化和细胞生物学功能进行表征；(3)按位置克隆Mdac。该实验旨在使用Dac/Mdac系统作为研究生长和发育模式中上皮-间充质相互作用的新切入点。由于Dac很可能是人类手足分裂畸形3基因的小鼠同源基因，该项目也可能与先天性肢体疾病的理解和诊断直接相关。

This project is part of a research program that seeks to understand molecular mechanisms of normal and abnormal limb pattern formation through the characterization of novel genes defined by mutations and polymorphisms in the mouse. Outgrowth and proximodistal patterning of the vertebrate embryonic limb require signaling by the apical ectodermal ridge (AER) to the progress zone (PZ), which proliferates in response and lays down the cells of the presumptive limb in a proximal to distal progression. The signaling loop between AER and PZ that is essential for sustaining outgrowth and patterning in the limb is disrupted in the antimorphic mouse mutation Dactylaplasia (Dac). Dac was cloned by position and found to encode a pioneer gene whose sequence reveals nothing about its function. The suppressor allele of a strain polymorphism, Modifier of Dactylaplasia (Mdac), has no phenotype on its own but dominantly suppresses Dac with 100 percent penetrance. The proposed research has three aims: (1) to understand the developmental function of the Dac gene by (a) generating and characterizing a targeted null allele and (b) determining the mechanism by which the two spontaneous mutations Dac1J and Dac2J exert their dominant effect; (2) to generate reagents (antibodies and a full length cDNA) that will allow future characterization of the biochemical and cell biological functions of the Dac gene; and (3) to clone Mdac by position. The experiments are designed to use the Dac/Mdac system as a novel entry point to investigate epithelial-mesenchymal interactions in growth and developmental patterning. Because Dac is likely to be the mouse ortholog of the human Split Hand/Foot Malformation 3 gene, this project may also bear direct relevance to understanding and diagnosis of congenital limb diseases.