Molecular and Physiological Function of the Tubby Gene Family

描述（由申请人提供）：我们已经描述了一个小基因家族，tubby样蛋白（TULP）。其创始成员tubby（TUB）的突变导致小鼠肥胖、视网膜和耳蜗变性的三联表型，这与在患有Alstrom或Bardet-Biedl综合征的个体中观察到的表型相似，所述Alstrom或Bardet-Biedl综合征由纤毛相关蛋白的突变引起。肥胖小鼠的迟发性、缓慢进展性肥胖反映了成熟期人类肥胖的常见形式。TUB基因的多态性已被证明与肥胖相关，TULP 1的突变导致人类视网膜色素变性和Leber先天性黑蒙。此外，Tulp 3的无效突变导致小鼠胚胎死亡。通过在高等真核生物中的进化和当它们突变时观察到的相关疾病，tubby基因家族的强保守性表明TULP在表达它们的细胞的正常功能中起重要作用。 目前，TULP的分子功能尚不清楚。然而，在tubby和Tulp 1突变小鼠的视网膜中含有视紫红质的囊泡的积累，以及与参与细胞内运输的基因和蛋白质的相互作用，表明TULP在这一过程中的作用。为了开始了解TUB的细胞功能，我们将在转基因小鼠中进行实验，这些实验将使用标记的TUB蛋白的高分辨率成像在与细胞内运输标记物的共定位研究中测试TUB是否在细胞运输中起作用。我们还将使用酵母双杂交分析和免疫沉淀来鉴定与TUB直接相互作用的蛋白质。这些研究将确定TUB参与的途径。 与缺乏对TULP细胞功能的了解类似，对TULP的破坏如何导致观察到的疾病表型的了解也有限。为了测试肥胖小鼠的肥胖是否是其在CNS或脂肪细胞或两者的组合中的破坏的结果，我们将分析在这两个位点单独破坏TUB的组织特异性靶向突变。我们将测试这一假设，即矮胖小鼠对棕色脂肪有慢性交感神经激活，从而限制了它们的肥胖。我们将通过产生TULP 3的他莫昔芬诱导型等位基因来检验TULP 3突变将导致成年动物肥胖和视网膜疾病的假设。最后，通过定位克隆，我们将确定一个遗传修饰的tubby突变，可以防止肥胖的tubby小鼠。这套实验将提供进入TULP作用途径的切入点，并深入了解其细胞功能，从而揭示其作用机制。 公共卫生相关性：我们的长期目标是了解tubby样蛋白（TULP）在细胞中的作用，以及这些蛋白质和初级纤毛（TULP相关的细胞结构）的缺陷如何导致几个器官系统和生物体的功能障碍。这个项目将进一步了解与初级纤毛相关的细胞内运输如何导致肥胖，这种联系最近才被Bardet-Biedl和Alstrom综合征的分析所认识。由于这些综合征包括在一般人群中常见的疾病，如肥胖，2型糖尿病和失明，了解TULP功能也有助于更好地了解这些疾病的常见形式。

DESCRIPTION (provided by applicant): We have described a small gene family, the tubby like proteins (TULP). Mutations in its founding member, tubby (TUB), cause a tripartite phenotype of obesity, retinal and cochlear degeneration in mice, which is similar to the phenotypes observed in individuals with Alstrom or Bardet-Biedl syndromes which are caused by mutations in ciliary associated proteins. The late onset, slowly progressing obesity in tubby mice is reflective of common forms of maturity onset human obesity. Polymorphisms in the TUB gene have been shown to be associated with obesity, and mutations in TULP1 cause retinitis pigmentosa and Leber's Congenital Amaurosis in human populations. Furthermore, a null mutation for Tulp3 leads to embryonic lethality in mice. A strong conservation of the tubby gene family through evolution in higher eukaryotes and the associated diseases observed when they are mutated, indicate that TULPs play an important role in the normal function of the cells in which they are expressed. Currently, the molecular function of TULPs is not known. However, accumulation of rhodopsin containing vesicles in the retina of tubby and Tulp1 mutant mice, and interaction with genes and proteins involved in intracellular trafficking, suggest a role for TULPs in this process. To begin to understand the cellular function of TUB, we will carry out experiments in genetically modified mice that will test whether TUB plays a role in cellular transport using high resolution imaging of labeled TUB protein in co-localization studies with markers of intracellular trafficking. We will also use yeast two hybrid analysis and immunoprecipitation to identify proteins that directly interact with TUB. These studies will define pathways in which TUB participates. Similar to the lack of knowledge about the cellular function of TULPs, there is also limited knowledge about how disruptions in TULPs lead to the observed disease phenotypes. To test whether the obesity in tubby mice is a result of its disruption in the CNS or in adipocytes or a combination of both, we will analyze tissue specific targeted mutations that inactivate TUB at both of these sites individually. We will test the hypothesis that tubby mice have chronic sympathetic activation to brown fat, thus limiting their obesity. We will test the hypothesis that mutations of TULP3 will lead to obesity and retinal disease in the adult animal by generating a tamoxifen inducible allele of TULP3. And finally, by positional cloning we will identify a genetic modifier of the tubby mutation that can prevent obesity in tubby mice. This suite of experiments will provide entry points into the pathways in which TULPs act and insight into their cellular function and, thereby, reveal their mechanisms of action. PUBLIC HEALTH RELEVANCE: Our long term goal is to understand the role that tubby like proteins (TULPs) play in the cell and how defects in these proteins and in the primary cilium, a cellular structure that TULPs are associated with, lead to dysfunction within several organ systems and the organism. This project will further our understanding of how intracellular trafficking associated with the primary cilium contributes to obesity, a connection that has only recently been recognized with the analyses of Bardet-Biedl and Alstrom syndromes. Since these syndromes comprise diseases that are common in the general population such as obesity, type 2 diabetes, and blindness, understanding TULP function may also contribute to a better understanding of the common forms of these diseases.