Role of APL-1, a C. elegans protein related to human amyloid precursor protein

描述(由申请人提供)：致密斑块的沉积和神经原纤维缠结的存在是阿尔茨海默病确诊的两个尸检标准。致密斑块的主要成分是一种由较大的淀粉样蛋白前体(APP)衍生的40个氨基酸的β-淀粉样多肽。在APP的处理过程中，已经提出了两种可供选择的途径，其中只有一种产生了β-淀粉样肽。APP的功能及其不同的切割产物仍然知之甚少。此外，这些蛋白质的功能途径还没有确定。哺乳动物中存在一个与APP相关的蛋白家族。在小鼠中敲除APP家族会导致出生后死亡和II型无脑畸形，这表明APP家族在发育过程中具有必要的功能。我们对研究APP的功能很感兴趣，并正在通过在一个简单的模式系统-线虫秀丽线虫中检测APP相关基因来解决这个问题。线虫具有实验上的优势，即易于进行基因操作，并能够快速产生转基因动物。我们已经鉴定出一种线虫基因APL-1，它编码一种APP相关蛋白。APL-1与APP家族蛋白具有很强的序列同源性和结构相似性。APL-1基因敲除导致幼虫死亡，可通过对APL-1基因组片段进行种系转化来挽救。有趣的是，APL-1的致死性也可以通过只编码APL-1的胞外区或驱动APL-1的泛神经表达的构建体来拯救。高水平的APL-1过表达导致对幼虫的不完全穿透致死，这表明APL-1的水平必须受到严格调控。我们建议：1)确定APL-1必须在哪些细胞中表达才能挽救致死性；2)确定在发育后期是否需要APL-1；3)阐明APL-1过表达动物致死性的潜在基础；4)确定高温如何影响APL-1的功能；以及5)确定在APL-1途径中起作用的基因。线虫提供了一个易于处理的遗传模型，在该模型中，许多不适用于哺乳动物系统的方法可以用来理解APL-1的功能。了解APL-1功能的途径可能会让我们深入了解人类APP的功能途径。公共卫生相关性：阿尔茨海默氏症影响着超过450万美国人。包括淀粉样前体蛋白(APP)基因在内的三个基因的突变与家族性阿尔茨海默病有关。然而，APP的功能还不清楚。我们正在研究遗传模型系统中与APP相关的基因--线虫线虫；来自线虫的信息可能会为APP在高等生物(如人类)中的正常功能提供线索。

DESCRIPTION (provided by applicant): Deposition of dense plaques and the presence of neurofibrillary tangles are two postmortem criteria used in the definitive diagnosis of Alzheimer's disease. The major component of the dense plaques is a 40 amino acid beta-amyloid peptide that is derived from a larger amyloid protein precursor (APP). Two alternative pathways have been suggested in the processing of APP, only one of which produces the beta-amyloid peptide. The function of APP and its different cleavage products are still poorly understood. Furthermore, the pathways in which the proteins function have not been identified. A family of APP- related proteins is present in mammals. Knockout of the APP family in mice leads to postnatal lethality and type II lissencephaly, indicating that the APP family has essential functions during development. We are interested in studying the function of APP and are approaching this problem by examining an APP- related gene in a simple model system, the nematode Caenorhabditis elegans. C. elegans has the experimental advantages of being easy to manipulate genetically and being able to generate transgenic animals quickly. We have identified a C. elegans gene, apl-1, that encodes an APP-related protein. APL- 1 has strong sequence homology and structural similarities with the APP family proteins. Knockout of apl-1 leads to larval lethality, which can be rescued by germline transformation of a apl-1 genomic fragment. Interestingly, the apl-1 lethality can also be rescued by transformation with constructs encoding only the extracellular domain of APL-1 or driving pan-neural expression of APL-1. High levels of APL-1 overexpression lead to an incompletely penetrant larval lethality, suggesting that levels of APL-1 must be tightly regulated. We propose to: 1) determine in which cells apl-1 must be expressed to rescue the lethality; 2) determine whether APL-1 is required during later developmental stages; 3) elucidate the underlying basis of the lethality in APL-1 overexpression animals; 4) identify how elevated temperatures affect APL-1 function; and 5) identify genes that act in the APL-1 pathway. C. elegans provides a tractable genetic model in which many approaches not feasible for use in mammalian systems can be used to understand APL-1 function. Understanding the pathways through which APL-1 functions may give insights into the pathways through which human APP functions. PUBLIC HEALTH RELEVANCE: Alzheimer's disease affects over 4.5 million Americans. Mutations in three genes, including the Amyloid Precursor Protein (APP) gene, have been correlated with familial Alzheimer's disease. However, the function of APP is still unknown. We are examining an APP-related gene in a genetic model system, the roundworm Caenorhabditis elegans; information from C. elegans is likely to provide clues into the normal function of APP in higher organisms, such as man.