The evolution of a co-opted gene-regulatory network underlying a rapidly evolving morphological trait

 描述(由申请人提供) 这项研究的目的是剖析一个快速进化的复杂性状背后的致病基因和突变，并了解制约该性状进化的因素的性质。这样的努力需要一个实验系统，在这个系统中，物种在很短的进化时间内发生剧烈变化，可以很容易地通过基因操作。果蝇种群中的后叶是雄性生殖器的一个新近衍生的结构特征，在交配中起重要作用。在过去的两百万年里，这一组中的四个物种中的每一个物种的结构都进化出了截然不同的形态。我们的初步工作记录了编码幼虫后气孔的高度保守的基因调控网络(GRN)在成年后叶中创造新的表型变异时的明显选择和重新部署。这一发现刺激我们假设，在保持气孔结构不变的情况下，允许快速进化的肺叶发生变化的机制。在这个GRN的成员中，我们已经证明了POX NERO(Poxn)基因在仿生杜鹃中相对于黑腹杜鹃表达不同地上调，并且像在仿生杜鹃中观察到的那样，在黑腹杜鹃中的过度表达导致叶的扩大。此外，我们还证明了poxn的上调是由基因中包含的后叶特异增强子中的序列差异引起的。使用群体遗传学方法来检测自然选择，我们已经识别出与poxn的后叶增强子一致的选择特征。在这里，我们建议使用基因组学(即RNA-SEQ，群体基因组学)和分子遗传学技术(即转基因表达和互补分析)来识别导致黑腹大鼠物种间后叶大小和形状差异的其他致病基因和突变(目标1和2)。有了大量这样的分子变化，我们将研究如何在不改变气孔结构的情况下，后叶的增选结节在叶功能上发生分歧(目标3)。

 DESCRIPTION (provided by applicant) The goal of this research is to dissect the causative genes and mutations underlying a rapidly evolving complex trait and to understand the nature of constraints on the evolution of this trait. Such an endeavor requires an experimental system in which drastic changes occur over short evolutionary timeframes in species that can be easily manipulated genetically. The posterior lobe in the Drosophila melanogaster species group is a recently-derived structural feature of male genitalia important in mating. The structure has evolved strikingly different morphology in each of the four species of this group over the past two million years. Our preliminary work has documented the apparent co-option and re-deployment of a highly conserved gene regulatory network (GRN) encoding the larval posterior spiracle in creating novel phenotypic variation in the adult posterior lobe. This finding stimulates us to hypothesize mechanisms that would allow the rapidly evolving lobe to change while leaving the spiracle structure unaltered. Among the members of this GRN is the gene pox neuro (poxn) which we have shown is divergently upregulated in D. simulans relative to D. melanogaster and that over-expression in D. melanogaster leads to enlargement of the lobe as observed in D. simulans. Additionally, we have shown that the upregulation of poxn in D. simulans is caused by sequence divergence in a posterior lobe-specific enhancer contained within the gene. Using a population genetic method to detect natural selection, we have identified a signature of selection that coincides with the posterior lobe enhancer of poxn. Here, we propose to employ genomic (i.e. RNA-seq, population genomics) and molecular genetic techniques (i.e. transgenic expression and complementation assays) to identify other causative genes and mutations responsible for differences in posterior lobe size and shape among species of the D. melanogaster species group (Aims 1 and 2). With a large collection of such molecular changes in hand, we will examine how co-opted nodes of the posterior lobe have diverged in their lobe functions without altering the spiracle structure (Aim 3).