Molecular Genetics of Drosophila Hybrid Lethality

描述(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。物种形成是在不同种群之间形成生殖障碍时发生的。种间杂交的不育性和致命性是一种生殖障碍。这些杂交不亲和性是由在每个分化的种群中独立进化的基因之间的有害相互作用造成的。这一建议是基于之前发现的两个基因Hmr和LHR，这两个基因相互作用，导致果蝇物种黑腹果蝇和拟果蝇之间的杂交致死。一个主要的目标是了解这些基因是如何杀死杂种的，以及它们之间的相互作用是如何与它们的DNA序列差异模式相关的。一种特殊的假设是，HMR和LHR通过扰乱染色质的结构和调节而导致杂交致死，染色质是DNA和相关蛋白质的复合体，控制基因调节、染色体复制和细胞分裂以及核形态的维持，并且对基因调控、染色体复制和细胞分裂至关重要。染色质相关蛋白的高分辨率成像和间期细胞核的细胞学研究将用于验证这一假说。HMR和LHR基因编码的蛋白质在杂交物种之间具有相对较高的序列差异。第二种假设是，这些分化的蛋白质将通过它们与染色质的相互作用定位于不同的DNA序列。这一假设将通过细胞学方法和进行染色质免疫沉淀(CHIP)然后对回收的DNA进行短读测序来验证。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在种间杂交中是否受到干扰。LHR基因差异的一个显著方面是，与黑腹葡萄球菌相比，模拟葡萄球菌的编码区含有大量的插入片段。一种不寻常的LHR等位基因被发现，该等位基因缺乏这种插入，并且与野生型等位基因相比有额外的序列变化。该等位基因不会导致杂交致死，将对其进行研究，以确定该插入是否导致黑腹盘藻和拟黑腹盘藻之间LHR基因的功能差异。已经发现基因组的一个区域似乎包含一种新的主效杂交致死基因。为了确定它是与HMR和LHR相互作用，还是定义了一条导致杂交致死的独立途径，将对该基因进行鉴定。 与公共卫生相关：该项目将提供对物种之间如何形成屏障的机械性理解。形成这些屏障的基因是使每个物种独一无二的一部分。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维持一个功能连贯的基因组。

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.