The role of RNA export factors in tissue specific gene expression

多细胞生物体中的单个细胞具有不同的形状和特征，每个细胞专门用于特定的功能。了解生物体功能的一个主要目的是了解细胞如何分化（分化）。多细胞生物体中的每个细胞都携带相同的基因。细胞通过表达与其最终功能相关的蛋白质的基因来分化，并抑制其蛋白质产物对于最终功能不需要（甚至是有害的）的基因。该项目旨在增加对控制分化细胞中基因表达的基本生物过程的理解。我们专注于精子的生产，因为精子是非常专业化的，它们的形成取决于大量基因的表达，这些基因在任何其他过程中都没有使用。我们使用果蝇，果蝇，作为一个模型系统，因为它是非常适合遗传和分子分析。由于这些过程是所有多细胞生物体的基础，我们希望我们的研究结果具有广泛的意义，例如在理解人类发育和疾病方面。基因的表达需要将DNA中的信息在细胞核中复制（转录）成RNA分子，然后将其运送到细胞质并翻译成蛋白质。基因表达在转录和翻译水平上都受到调控。RNA在细胞核中的加工以及从细胞核中的输出也是控制点。RNA从细胞核输出到细胞质的机制已经被很好地描述，并且依赖于一组从酵母到人类都保守的蛋白质。在转录水平上基因表达的调节依赖于基因“启动子”附近特定区域的DNA，这些区域具有被序列特异性DNA结合蛋白（转录因子）结合的序列。这些转录因子与基因启动子的结合然后募集一种酶复合物（RNA聚合酶），该酶复合物实际上转录DNA序列以产生RNA转录物。通常，这包含插入序列（内含子），这些插入序列被剪接出来以产生最终的mRNA产物。转录过程，特别是剪接，促进RNA输出蛋白与mRNA的结合。在我们最近的研究中，我们发现在精子发育中，RNA输出途径的一个组成部分是睾丸特异性转录本表达所必需的，而不是大多数其他转录本。我们已经证明，这是因为RNA输出因子，被认为是在转录因子下游调节基因表达，实际上也反馈促进睾丸中特定转录因子的活性。如果没有这种反馈，专门制造精子所需的基因就不会表达，果蝇就会不育。我们的项目目的是了解这种反馈的机制。是涉及整个出口途径，还是仅涉及具体部分？输出因子是否直接与转录因子结合？输出因子促进转录因子与DNA的结合，还是促进转录因子募集RNA聚合酶的活性？转录因子是否有助于保护睾丸特异性RNA免受降解？我们还发现，RNA输出活性的降低使雌性不育，并导致许多个体动物因腐败而死亡。这些影响是非常具体的，似乎不是由于RNA输出的一般失败，而是像睾丸中的情况一样，由特定转录程序的缺陷引起的。我们将调查我们的研究结果之间的联系，转录和RNA输出的特点，在这些其他的发展背景下的基因表达缺陷的一般性。我们希望识别相关的转录因子，并以我们从睾丸中的发现为指导，开发机制见解。

Individual cells in multicellular organisms are have distinct shapes and characteristics, each specialised for a specific function. A major aim in understanding organism function is to understand how cells become specialised (differentiated). Every cell in a multicellular organism carries the same genes. Cells differentiate by expressing genes for proteins relevant to their final function, and repressing genes whose protein products are not needed (or are even detrimental) for the final function. This project is aimed at increasing understanding of the fundamental biological processes that control gene expression in differentiating cells. We focus on sperm production, since sperm are extremely specialised, and their formation depends on expression of a very large number of genes not used in any other process. We use the fruit fly, Drosophila melanogaster, as a model system as it is highly amenable to a genetic and molecular analysis. Since these processes fundamental to all multi-cellular organisms, we expect our results to have broad implications, eg in understanding human development and disease.Expression of genes requires copying (transcribing) information from DNA, in the cell nucleus, into an RNA molecule that is then transported to the cytoplasm and translated into protein. Gene expression is well known to be regulated at both transcriptional and translational levels. RNA processing in the nucleus, and export from the nucleus, also present control points. The mechanism by which RNAs get exported from the nucleus to the cytoplasm is well characterised, and relies on a set of proteins that are conserved from yeasts to humans.Regulation of gene expression at the transcriptional level relies on the DNA of specific regions near genes "promoters" having sequences that are bound by sequence-specific DNA binding proteins (transcription factors). Binding of these transcription factors to gene promoters then recruits an enzyme complex (RNA polymerase) that actually transcribes the DNA sequence to give an RNA transcript. Usually this contains intervening sequences (introns) that get spliced out to make the final mRNA product. The process of transcription, and particularly splicing, promotes binding of the RNA export proteins to the mRNA. RNAs that are not appropriately processed are degraded.In our recent research we discovered that a component of the RNA export pathway is required for expression of testis-specific transcripts, but not most other transcripts, in sperm development. We have shown that this is because the RNA export factors, which are understood to work downstream of the transcription factors in regulation of gene expression, actually also feed back to promote activity of a specific transcription factor in testes. Without this feedback the genes required specifically to make sperm are not expressed, and the flies are sterile.Our project aim is to understand the mechanism of this feedback. Is the whole export pathway involved, or only specific components? Do the export factors directly bind to the transcription factors? Do the export factors promote binding of the transcription factors to the DNA, or do they promote the transcription factors activity in recruiting the RNA polymerase? Does the transcription factor help protect the testis-specific RNAs from degradation?We also found that reducing activity of the RNA export makes the females sterile, and causes many individual animals to die as pupae. These effects are very specific, and don't appear to be due to a general failure in RNA export, but appear, like the situation in testes, to be caused by defects in specific transcription programmes. We will investigate the generality of our findings on the link between transcription and RNA export by characterising the gene expression defects in these other developmental contexts. We hope to identify the relevant transcription factor, and develop mechanistic insights using our findings from testes as a guide.