Functional Genomics of Inversion 2La in Anopheles gambiae

描述(申请人提供)：恶性疟原虫引起的疟疾每年夺走300万儿童的生命，主要发生在非洲。目前还没有疫苗，仅靠化学预防不太可能显著减少传播。除了杀虫剂抗药性的威胁外，现有的侧重于室内使用杀虫剂的病媒控制策略可能无法达到所有传播疾病的人群，或者可能导致行为转变，因为病媒休息和叮咬行为的潜在种群异质性--即使是被认为主要是“嗜内性”和“食虫性”(室内休眠和叮咬)的媒介，如冈比亚按蚊。在非洲，冈比亚按蚊是最重要的媒介。这种蚊子迅速适应了气候多样化和人为环境。有助于其适应性的是多态染色体倒置。特别相关的是2号染色体左臂(21a或+a)上的替代排列，它们通过完全未知的生理和/或行为机制优先与不同的环境(干旱和潮湿)相关。根据2LA的频率分布图，这种排列在干旱稀树草原达到100%，而在湿润雨林中仅发现可供选择的排列(2L+a)。因此，如果没有2LA的好处，冈比亚按蚊将仅限于雨林地区，在那里这种蚊子不一定是最多的、甚至不是最好的疟疾媒介。在当地，2LA在旱季和夜间室内休息的样本中达到最高频率，那里的夜间饱和赤字较高。因此，2LA通过对室内叮咬和休息行为的影响，影响了一个关键的流行病学特征--媒介与人类接触的可能性，以及媒介接触到经杀虫剂处理的墙壁和蚊帐的可能性。该项目的最终目标是确定2LA中赋予抗旱性的基因和基因网络--干旱是导致媒介与人类接触增加和疟疾在当地和地理范围内传播的一种或一套表型。为了实现这一目标，我们提出了一种结合表型和分子分析的多学科综合方法，通过三个具体目标开始梳理2LA的功能基因组：(1)识别与2LA的替代排列相关的表型性状；(2)识别可能导致表型差异的排列之间的序列差异；(3)通过比较基因表达模式，将基因和表型差异联系起来。该计划的短期结果将是适应性表型和潜在候选基因之间的联系，导致关于2LA如何赋予对干旱的抗性并影响媒介与人类接触的可能性的具体假设。较长期的好处是双重的。首先是改进病媒控制的实施、评估和设计，其基础是对我们现在所称的“适应性灵活性”的机械性理解。换句话说，对2LA与干旱耐受性和室内休息行为相关的遗传、生理和行为属性的详细了解将显著提高我们预测现有和新的媒介控制策略的流行病学影响的能力，并可能导致设计更全面的策略来抵抗媒介种群的组成部分的逃避。第二个好处是，2LA抗旱性功能基因组研究的成功结果将为研究冈比亚沙打旺许多其他重要医学性状的功能基因组学提供通用模型。与公共卫生相关的现有控制战略由于耐药性的发展而不充分和受到威胁。需要新的媒介控制战略，特别是对非洲疟疾的主要媒介冈比亚按蚊。在这种蚊子中，在重排的染色体上进行的基因变异(称为染色体倒置)赋予了在对比(干旱或潮湿)环境中传播媒介成功所必需的特征。因此，它们会影响媒介生物在季节和空间上的分布，包括室内休息和叮咬行为。因此，它们影响一个关键的流行病学特征--媒介与人类接触的可能性--以及媒介接触经杀虫剂处理的墙壁和蚊帐的可能性。不幸的是，载体种群中这些异质性背后的相关遗传、生理和行为机制是完全未知的。对这些特征的详细了解将显著提高我们预测现有和新的媒介控制策略的流行病学影响的能力，并可以导致设计更全面的策略，以抵抗媒介种群的组成部分的逃避。

DESCRIPTION (provided by applicant): Malaria caused by Plasmodium falciparum claims the lives of three million children per year, mainly in Africa. A vaccine is not available and chemoprophylaxis alone is unlikely to significantly reduce transmission. Aside from the threat of insecticide resistance, existing vector control strategies that focus on indoor use of insecticides may not reach all of the disease-transmitting population or may induce a behavioral shift, given underlying population heterogeneities in vector resting and biting behavior-- even in vectors considered to be primarily "endophilic" and "endophagic" (indoor resting and biting) such as Anopheles gambiae. In Africa, A. gambiae is the most important vector. This mosquito has adapted rapidly to climatically diverse and anthropogenic environments. Instrumental to its adaptive flexibility are polymorphic chromosomal inversions. Of particular relevance are alternative arrangements on the left arm of chromosome 2 (2La or +a) that are preferentially associated with contrasting environments (arid and humid) through entirely unknown physiological and/or behavioral mechanisms. Based on frequency distribution maps of 2La, this arrangement reaches 100% in arid savannas while in humid rainforests only the alternative arrangement (2L+a) is found. Thus without the benefit of 2La, A. gambiae would be limited to rainforest areas where this mosquito is not necessarily the most abundant or even the best malaria vector. At a local level, 2La reaches its highest frequency during the dry season and in samples captured resting indoors at night where the nocturnal saturation deficit is higher. Thus 2La influences a key epidemiological trait-- the probability of vector-human contact-- as well as the likelihood of vector exposure to insecticide-treated walls and bed nets, through its effect on indoor biting and resting behavior. The ultimate goal of this project is to identify the genes and gene networks in 2La that confer resistance to aridity-- a phenotype or suite of phenotypes that leads to increased vector-human contact and malaria transmission at both local and geographic scales. To achieve this goal, we propose a multidisciplinary and integrative approach that combines phenotypic and molecular analysis to begin to tease apart the functional genomics of 2La through three specific aims: (1) Identify phenotypic traits associated with alternative arrangements of 2La; (2) Identify sequence differences between arrangements that may contribute to phenotypic differences; (3) Associate genotypic and phenotypic differences by comparing patterns of gene expression. The short-term outcome of this program will be linkages between adaptive phenotypes and underlying candidate genes, leading to specific hypotheses about how 2La confers resistance to aridity and impacts the probability of vector-human contact. The longer term benefits are two-fold. The first is improved implementation, evaluation and design of vector control, based on a mechanistic understanding of what we now call "adaptive flexibility". In other words, gaining a detailed understanding of genetic, physiological and behavioral attributes of 2La that are linked to aridity tolerance and indoor resting behavior will significantly improve our ability to predict the epidemiological impact of existing and novel vector control strategies, and can lead to the design of more comprehensive strategies resistant to evasion by components of the vector population. The second benefit is that a successful outcome in the study of functional genomics of aridity resistance in 2La will serve as a general model for studying the functional genomics of many other medically important traits in A. gambiae. PUBLIC HEALTH RELEVANCE Existing control strategies are inadequate and threatened due to development of resistance. Novel vector control strategies are needed, especially for the primary African malaria vector Anopheles gambiae. In this mosquito, genic variations carried on rearranged chromosomes (known as chromosomal inversions) confer traits that are essential to vector success in contrasting (arid or humid) environments. As such, they impact vector distribution seasonally and spatially, including indoor resting and biting behavior. Therefore, they influence a key epidemiological trait-- the probability of vector-human contact-- as well as the likelihood of vector exposure to insecticide-treated walls and bed nets. Unfortunately, the relevant genetic, physiological and behavioral mechanisms underlying these heterogeneities in the vector population are completely unknown. Detailed understanding of these traits will significantly improve our ability to predict the epidemiological impact of existing and novel vector control strategies, and can lead to the design of more comprehensive strategies resistant to evasion by components of the vector population.