Genetic dissection of skeletal patterning

描述(由申请人提供)：同源框基因在脊椎动物骨骼图案形成中的关键作用已经得到了很好的证实。关于特定的HOX基因在特定骨骼区域的特异性和协同性已知很多，但尽管在许多实验室进行了10多年的功能实验，但仍然不知道HOX转录因子实际上是如何控制脊椎的特性的。发育中的骨架中的转录靶标也尚未确定，这是从机制上理解HOX调节途径的主要障碍。在这里，我提出了一种识别HOX控制通路的遗传学方法；这是骨骼图案化领域的一个新方向。核心假设是，骨骼模式--由HOX基因调控--表现为一种数量性状，受基因-基因和基因-环境相互作用的控制。这一命题得到了我们实验室大量数据的支持，这些数据证明了骨骼中存在HOX基因功能的营养和遗传修饰物。我们已经证明：(I)遗传因素调节Hoxb6基因敲除小鼠骨骼异常的严重程度；(Ii)表型表现受发育胚胎本身的遗传背景控制；(Iii)不同的骨骼元素受区域特定途径的影响，这些途径在很大程度上是独立运行的；以及(Iv)遗传修饰物的数量很少，因此实验上是容易处理的。我们现在的主要目标是通过追求以下具体目标来定义在骨骼模式中与HoxbG相互作用的遗传因素： (1)利用微卫星标记全基因组扫描技术，对以C57BI/6和129Sv/EV为背景的Hoxb6突变株回交，定位了品系特异性遗传修饰基因S的基因组位置； (2)通过分析Hoxb6突变的FVB遗传背景，明确遗传修饰物对Hoxb6突变体骨纹表型表现的影响； (3)研究在Hoxb6基因突变表型发病机制中已知的骨型中介基因的表达情况。 作用于骨骼模式的修饰基因的识别将揭示骨骼发育的新的分子机制，并对脊椎动物身体计划的进化具有重要意义。

DESCRIPTION (provided by applicant): The crucial role of homeobox genes in patterning of the vertebrate skeleton is well established. Much is known about the specificity and cooperation of particular Hox genes in defined skeletal regions, but despite more than 10 years of functional experiments in numerous laboratories, it is still unknown how Hox transcription factors actually control vertebral identity. The transcriptional targets in the developing skeleton also have not been identified, a major obstacle to a mechanistic understanding of Hox regulated pathways. Here, I propose a genetic approach to the identification of Hox-controlled pathways; a new direction in the field of skeletal patterning. The central hypothesis is that skeletal patterning-- as regulated by Hox genes--manifests as a quantitative trait, which is controlled by gene-gene and gene-environment interactions. This proposition is supported by extensive data from our laboratory that demonstrate the existence of nutritional and genetic modifiers of Hox gene function in the skeleton. We have shown that (i) genetic factors modulate severity of skeletal anomalies in Hoxb6 knockout mice; (ii) phenotype manifestation is controlled by genetic background of the developing embryo itself; (iii) distinct skeletal elements are affected by region-specific pathways that operate largely independently; and that (iv) the number of genetic modifiers is small, and therefore experimentally tractable. Our major goal now is to define the genetic factors that interact with HoxbG in skeletal patterning by pursuit of the following Specific Aims: (1) to map the genomic location of the strain-specific genetic modifier(s) by microsatellite marker whole genome scan in a backcross of Hoxb6 mutants on C57BI/6 and 129Sv/Ev backgrounds; (2) to define the influence of genetic modifiers on manifestation of skeletal patterning phenotypes in Hoxb6 mutants by analyzing the mutation on the FVB genetic background; and (3) to characterize the expression of genes that are known mediators of skeletal patterning for their function in pathogenesis of Hoxb6 mutant phenotypes. The identification of modifier loci that act on skeletal patterning will reveal new molecular mechanisms in skeletal development and has important implications for the evolution of vertebrate body plans.