Fuller Zachary L, Haynes Gwilym D, Richards Stephen, Schaeffer Stephen W
Department of Biology, Pennsylvania State University, University Park, Pennsylvania 16802-5301.
Department of Biology, Pennsylvania State University, University Park, Pennsylvania 16802-5301
Genetics. 2016 Sep;204(1):287-301. doi: 10.1534/genetics.116.191429. Epub 2016 Jul 8.
Chromosomal rearrangements can shape the structure of genetic variation in the genome directly through alteration of genes at breakpoints or indirectly by holding combinations of genetic variants together due to reduced recombination. The third chromosome of Drosophila pseudoobscura is a model system to test hypotheses about how rearrangements are established in populations because its third chromosome is polymorphic for >30 gene arrangements that were generated by a series of overlapping inversion mutations. Circumstantial evidence has suggested that these gene arrangements are selected. Despite the expected homogenizing effects of extensive gene flow, the frequencies of arrangements form gradients or clines in nature, which have been stable since the system was first described >80 years ago. Furthermore, multiple arrangements exist at appreciable frequencies across several ecological niches providing the opportunity for heterokaryotypes to form. In this study, we tested whether genes are differentially expressed among chromosome arrangements in first instar larvae, adult females and males. In addition, we asked whether transcriptional patterns in heterokaryotypes are dominant, semidominant, overdominant, or underdominant. We find evidence for a significant abundance of differentially expressed genes across the inverted regions of the third chromosome, including an enrichment of genes involved in sensory perception for males. We find the majority of loci show additivity in heterokaryotypes. Our results suggest that multiple genes have expression differences among arrangements that were either captured by the original inversion mutation or accumulated after it reached polymorphic frequencies, providing a potential source of genetic variation for selection to act upon. These data suggest that the inversions are favored because of their indirect effect of recombination suppression that has held different combinations of differentially expressed genes together in the various gene arrangement backgrounds.
染色体重排可通过改变断点处的基因直接塑造基因组中遗传变异的结构，或者由于重组减少而将遗传变异组合在一起，从而间接塑造其结构。果蝇的第三条染色体是一个模型系统，可用于检验有关重排在种群中如何建立的假设，因为其第三条染色体对于由一系列重叠倒位突变产生的30多种基因排列具有多态性。间接证据表明这些基因排列是经过选择的。尽管存在广泛基因流的预期同质化效应，但这些排列的频率在自然界中形成梯度或渐变群，自该系统在80多年前首次被描述以来一直保持稳定。此外，在几个生态位中都存在频率可观的多种排列，这为异核型的形成提供了机会。在本研究中，我们测试了在一龄幼虫、成年雌性和雄性中，基因在不同染色体排列之间是否存在差异表达。此外，我们还询问了异核型中的转录模式是显性、半显性、超显性还是亚显性。我们发现有证据表明，在第三条染色体的倒位区域存在大量差异表达基因，其中包括雄性中参与感官感知的基因富集。我们发现大多数基因座在异核型中表现出加性。我们的结果表明，多个基因在排列之间存在表达差异，这些差异要么是由最初的倒位突变捕获的，要么是在其达到多态频率后积累的，这为选择作用提供了潜在的遗传变异来源。这些数据表明，倒位受到青睐是因为它们具有抑制重组的间接效应，这种效应在各种基因排列背景中将差异表达基因的不同组合聚集在一起。
