Molecular Genetics of Drosophila Hybrid Lethality

描述（由申请人提供）：了解新物种如何形成是生物学中的一个基本问题。物种形成是由于不同种群之间形成了生殖障碍。种间杂种的不育性和致死性是繁殖障碍的一种类型。这些杂交不亲和性是由在每个分化群体中独立进化的基因之间的有害相互作用引起的。这一建议是基于先前鉴定的两个基因，Hmr和Lhr，它们相互作用导致果蝇物种黑腹果蝇和果蝇之间的杂交致死。一个主要目标是了解这些基因如何杀死杂交种，以及它们之间的相互作用如何与它们的DNA序列差异模式相关。一个具体的假设是，Hmr和Lhr通过破坏染色质的结构和调节引起杂种致死性，染色质是DNA和相关蛋白质的复合物，其控制基因调节、染色体复制和细胞分裂以及维持核形态并且对于基因调节、染色体复制和细胞分裂以及维持核形态是必需的。染色质相关蛋白质的高分辨率成像和间期核的细胞学研究将被用来验证这一假设。Hmr和Lhr基因编码在杂交物种之间具有相对高的序列差异的蛋白质。第二个假设是，这些分歧的蛋白质将通过与染色质的相互作用定位到不同的DNA序列。将通过细胞学方法和染色质免疫沉淀（ChIP），然后对回收的DNA进行短读测序来检验这一假设。还将研究HMR和LHR编码的蛋白质之间的相互作用，以确定这些相互作用是否在种间杂交中被破坏。Lhr基因分歧的一个显著方面是D. simulans与D.黑腹菌在D. simulans缺乏这种插入，并且与野生型等位基因相比具有额外的序列变化。该等位基因不引起杂种致死性，将对其进行研究以确定插入是否有助于D. melanogaster和D. simulans。已经发现基因组的一个区域似乎含有一个新的主效杂交致死基因。将鉴定该基因，以确定其是否与Hmr和Lhr相互作用，或者相反定义导致杂交致死性的独立途径。 公共卫生相关性：该项目将提供一个物种之间如何形成障碍的机械理解。形成这些障碍的基因是使每个物种独特的一部分。了解这些基因进化模式的后果将有助于揭示包括人类在内的物种如何保持功能一致的基因组。

DESCRIPTION (provided by applicant): Understanding how new species form is a fundamental problem in biology. Speciation occurs as reproductive barriers form between diverging populations. One type of reproductive barrier is the sterility and lethality of interspecific hybrids. These hybrid incompatibilities are caused by deleterious interactions between genes that have evolved independently in each diverging population. This proposal is based on the previous identification of two genes, Hmr and Lhr, which interact to cause hybrid lethality between the fruit fly species Drosophila melanogaster and Drosophila simulans. A major goal is to understand how these genes kill hybrids, and how the interaction between them is related to their patterns of DNA sequence divergence. One specific hypothesis is that Hmr and Lhr cause hybrid lethality by disrupting the structure and regulation of chromatin, the complex of DNA and associated proteins that controls and is essential for gene regulation, chromosome replication and cell division, and the maintenance of nuclear morphology. High-resolution imaging of chromatin-associated proteins and cytological studies of interphase nuclei will be used to test this hypothesis. The Hmr and Lhr genes encode proteins that have relatively high sequence divergence between the hybridizing species. A second hypothesis is that these diverged proteins will localize to different DNA sequences through their interactions with chromatin. This hypothesis will be tested by cytological methods and by performing chromatin immunoprecipitation (ChIP) followed by short- read sequencing of the recovered DNA. Interactions between the proteins encoded by Hmr and Lhr will also be investigated to determine whether these interactions are disrupted in interspecific hybrids. One striking aspect of the divergence of the Lhr gene is that D. simulans contains a substantial insertion in its coding region compared to D. melanogaster. An unusual Lhr allele has been discovered from D. simulans that lacks this insertion and has additional sequence changes compared to wild type alleles. This allele does not cause hybrid lethality and it will be investigated in order to determine whether the insertion contributes to functional differences in the Lhr gene between D. melanogaster and D. simulans. A region of the genome has been found that appears to contain a new major-effect hybrid lethality gene. This gene will be identified in order to determine whether it interacts with Hmr and Lhr or instead defines an independent pathway leading to hybrid lethality. PUBLIC HEALTH RELEVANCE: This project will provide a mechanistic understanding of how barriers between species form. The genes that form these barriers are part of what makes each species unique. Understanding the consequences of the evolutionary patterns of these genes will help to reveal how species including humans maintain a functionally coherent genome.