GENETIC ANALYSIS OF EARLY LIMB DEVELOPMENT

该项目是一项研究计划的一部分，该计划旨在通过对小鼠突变和多态性定义的新基因的表征来了解正常和异常肢体模式形成的分子机制。 脊椎动物胚胎肢的向外生长和近远侧模式需要顶端外胚层嵴（AER）向进展区（PZ）发出信号，进展区（PZ）响应增殖并以近侧到远侧进展的方式放置假定肢的细胞。 AER和PZ之间的信号传导回路对于维持肢体的生长和模式至关重要，在反形态小鼠突变Dactylaplasia（Dac）中被破坏。Dac是通过位置克隆的，发现它编码一个先驱基因，其序列没有揭示它的功能。 一种菌株多态性的抑制等位基因，即Dactylaplasia修饰子（Modifier of Dactylaplasia，Mactylaplasia），本身没有表型，但以100%的等位率显性抑制Dac。本研究有三个目的：（1）通过（a）产生和表征靶向无效等位基因和（B）确定两个自发突变Dac 1 J和Dac 2 J发挥其显性效应的机制来理解Dac基因的发育功能;（2）生成试剂（抗体和全长cDNA），这将允许将来表征Dac基因的生物化学和细胞生物学功能;和（3）通过位置克隆Mc。 实验的目的是使用Dac/MPEG4系统作为一个新的切入点，调查上皮间充质相互作用的生长和发育模式。 由于Dac很可能是人类手/足裂畸形3基因的小鼠直系同源物，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.