GENETIC ANALYSIS OF EARLY LIMB DEVELOPMENT

这个项目是一个研究项目的一部分，该项目试图通过表征由小鼠的突变和多态定义的新基因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突起和近端模式需要通过顶端外胚层脊(AER)向进展区(PZ)发出信号，进展区作为响应而增殖，并将假定肢体的细胞放置在近端的远端进展中。AER和PZ之间的信号环对于维持肢体的生长和图案是必不可少的，但在抗变形小鼠突变指(DAC)中被破坏。DAC是按位置克隆的，并被发现编码一个先锋基因，该基因的序列没有揭示其功能。一种菌株的多态抑制等位基因，指趾发育的修饰性基因(MDAC)本身没有表型，但以100%的外显率抑制DAC。这项研究有三个目的：(1)通过(A)产生和鉴定目标零等位基因和(B)确定两个自发突变Dac1J和Dac2J发挥其显性作用的机制；(2)产生试剂(抗体和全长cDNA)，以便将来描述DAC基因的生化和细胞生物学功能；以及(3)通过位置克隆MDAC。本实验旨在利用DAC/MDAC系统作为一个新的切入点来研究生长和发育模式中的上皮-间充质相互作用。由于DAC很可能是人类手足分裂畸形3基因的小鼠直系同源基因，因此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.