Hox Regulation of Sensory Organ Development in Drosophila

描述（由申请人提供）：细胞如何解释位置信息以正确分化并形成不同的组织和器官是发育生物学中的一个基本问题。例如，在神经系统中，许多神经元亚型和感觉器官在精确定义的位置形成。该提案的长期目标是了解Hox转录因子提供的前后位置信息如何与神经元分化途径相结合，以决定体内不同神经元和感觉器官的类型，数量和位置。使用果蝇作为模式生物，我们专注于了解如何一个特定的Hox因子，腹-A（Abd-A），通过激活菱形（rho）调节感觉器官的形成。rho编码一种蛋白酶，其处理表皮生长因子（EGF）配体以诱导额外的神经元和一组肝细胞样细胞。通过生物信息学和转基因报告分析，我们确定了两个Hox调节rho增强子在腹部感觉神经元的特定子集中表达。保守的增强子区域的生物化学和遗传学表征揭示了Hox因子及其保守的辅因子Extradenticle（Exd）和Homothorax（Hth）用于刺激基因表达的新机制：Abd-A通过直接竞争DNA结合位点来拮抗无意义（Sens）（一种神经元锌指蛋白）的转录抑制。Sens及其脊椎动物同源物生长因子独立性-1（Gfi 1）是果蝇和小鼠感觉器官发育的关键调节因子。我们假设Hox-Sens拮抗作用是基因调控的一般机制。该假设以及其他Hox-神经元转录因子相互作用的鉴定将在以下目的中进行测试：1）确定Abd-A刺激rho所使用的机制，2）测试Hox-Sens竞争在基因表达调节中的作用，以及3）鉴定在ch器官SOP细胞中调节rho的其他神经元输入。这些实验利用了果蝇中可用的遗传工具，与脊椎动物不同，果蝇包含一组非冗余的Hox因子。除了控制神经元发育外，Hox、Exd、Hth和Sens脊椎动物同系物都调节血细胞形成，并与白血病有关。因此，Hox和Sens/Gfi 1分子机制与人类发育和疾病有关。 公共卫生相关性：我们已经确定了两个调节神经和血液系统发育的因素。这项资助的重点是这些因素如何发挥作用，以果蝇为模型系统指定感觉器官。由于这两个因素都与白血病有关，我们的研究可能会对人类发育和疾病产生新的见解。

DESCRIPTION (provided by applicant): How cells interpret positional information to properly differentiate and form distinct tissues and organs is a fundamental problem in developmental biology. In the nervous system, for example, numerous neuronal subtypes and sensory organs form at precisely defined positions. The long-term goal of this proposal is to understand how anterior- posterior positional information provided by Hox transcription factors is combined with neuronal differentiation pathways to dictate the type, number, and location of different neurons and sensory organs in the body. Using Drosophila as a model organism, we are focused on understanding how a specific Hox factor, Abdominal-A (Abd-A), modulates sensory organ formation by activating rhomboid (rho). rho encodes a protease that processes an epidermal growth factor (EGF) ligand to induce additional neurons and a set of hepatocyte-like cells. Through bioinformatics and transgenic reporter assays, we identified two Hox-regulated rho enhancers expressed in a specific subset of abdominal sensory neurons. The biochemical and genetic characterization of a conserved enhancer region uncovered a novel mechanism used by Hox factors and their conserved co-factors Extradenticle (Exd) and Homothorax (Hth) to stimulate gene expression: Abd- A antagonizes transcriptional repression by Senseless (Sens), a neuronal zinc finger protein, through direct competition for DNA binding sites. Sens and its vertebrate homologues Growth factor independence-1 (Gfi1) are critical regulators of sensory organ development in both the fly and mouse. We hypothesize that Hox-Sens antagonism is a general mechanism of gene regulation. This hypothesis as well as the identification of other Hox-neuronal transcription factor interactions will be tested in the following aims: 1) Determine the mechanisms used by Abd-A to stimulate rho, 2) Test the role of Hox- Sens competition in the regulation of gene expression, and 3) Identify additional neuronal inputs that regulate rho in ch organ SOP cells. These experiments take advantage of genetic tools available in Drosophila, which unlike in the vertebrate, contain a single set of non-redundant Hox factors. In addition to controlling neuronal development, the Hox, Exd, Hth, and Sens vertebrate homologues all regulate blood cell formation and have been implicated in leukemia. Thus, the Hox and Sens/Gfi1 molecular mechanisms uncovered in this grant are relevant to human development and disease. Public Health Relevance: We have identified two factors that regulate nervous and blood system development. This grant is focused on how these factors function to specify sensory organs using the fruit fly as a model system. As both factors have been implicated in leukemia, our studies are likely to shed new insight into both Human development and disease.