Genetic and molecular analysis of mutations in Drosophila melanogaster that lead to differences in expression of microRNA mir-92a and underlie phenotypic evolution

将形态特征的变异与潜在的遗传变异联系起来是进化生物学的一个目标。在不同种类的果蝇中，有一个特征是不同的，但在每个物种中通常是不变的，那就是“裸谷”的大小，即第二腿上裸露的角质层斑块。然而，几个种群的黑腹果蝇显示出裸谷的大小差异。潜在的遗传变异已经定位到一个包含microRNA mir-92a的位点，mir-92a位于蛋白质编码基因jigr1的内含子中。Mir-92a转录后调控shavenoid (sha)，这是一种参与裸谷发育的基因。我将首先研究jigr1或第二个蛋白质编码基因Npl4参与裸谷发育的可能性。mir-92a在不同果蝇品系中的表达差异被认为是随后sha差异调控裸谷大小变化的基础。mir-92a的差异表达可能是由增强子的突变促进的。我将分析mir-92a和jigr1的表达是否相关，从而受到相同顺式调控元件的控制。为了确定大小决定元件，我将使用GAL4-UAS系统在小裸谷遗传背景下，分别在大裸谷菌株和小裸谷菌株的候选增强子的控制下表达GFP和mir-92a。我将通过基于pcr的诱变，逐步改变大裸谷发展的增强子，以确定具有小裸谷的菌株的特性，从而确定负责大小变化的特定突变。这些实验结果将有助于确定黑腹果蝇裸谷表型变异的突变。

It is a goal of evolutionary biology to link the variation of morphological traits to the underlying genetic variation. A trait that differs between different Drosophila species but is usually constant within each species is the size of the naked valley, a naked cuticle patch on the second leg. However, several populations of Drosophila melanogaster show size differences of the naked valley. The underlying genetic variation has been mapped to a locus containing a microRNA, mir-92a, which is located in an intron of the protein-coding gene jigr1. mir-92a post-transcriptionally regulates shavenoid (sha), a gene involved in naked valley development. I will first examine the possibility of jigr1 or a second protein-coding gene, Npl4, being involved in the development of the naked valley, as well. Differences in expression of mir-92a in the different Drosophila strains are thought to underlie the naked valley size variation by subsequent differential regulation of sha. Differential expression of mir-92a is likely to be facilitated by mutations in an enhancer. I will analyse whether expression of mir-92a and jigr1 is correlated and thus controlled by the same cis-regulatory elements. In order to identify the size-determining element, I will use the GAL4-UAS system to express GFP as well as mir-92a under control of candidate enhancers from strains with large and small naked valleys, respectively, in the genetic background of a small naked valley. I will identify the specific mutations responsible for the size variation by stepwise altering the enhancer for development of a large naked valley towards the identity of a strain with a small naked valley by PCR-based mutagenesis. The results of these experiments will facilitate the identification of the mutations underlying phenotypic variation of the naked valley within Drosophila melanogaster.