The Role of Nutrition as an Epigenetic Modulator of Phenotypic Plasticity during Honeybee Development

蜜蜂是昆虫传粉者，占世界粮食生产价值的10%左右。它们生活在由成千上万个个体组成的复杂社会中，其中大多数是雌性工蜂，它们无法繁殖，而是将它们短暂的生命用于在花中寻找食物（花蜜/花粉）和其他任务，如护理幼虫。除了这些不育的雌蜂，蜂箱里还有雄蜂和一只被称为“蜂后”的雌蜂，它的寿命要长得多，可以繁殖。蚁后可以产下受精卵或未受精卵。未受精卵被喂食蜂胶，然后是花蜜/花粉，成为雄蜂，而受精卵可以成为蜂王或工蜂。受精卵产生的幼虫能否成为工蜂或蜂王取决于幼虫被喂食的食物类型。注定成为工蜂的幼虫喂食工蜂果冻，然后喂食花蜜/花粉，而注定成为蜂王的幼虫喂食蜂王浆。这些不同的饮食在成虫的一生中都保持着。单个蜜蜂幼虫成为蜂王、工蜂或雄蜂的能力不可能是因为不同的DNA：幼虫的基因组有能力成为这三者，这是由于基因的开启或关闭方式对特定的饮食做出反应；这决定了不同的发展结果。表观遗传学是一套动态的指令，它存在于遗传信息之上，可以对固定的DNA序列进行编码并指导多种不同的结果。表观遗传机制主要有两个家族；一种类型标记了实际的DNA序列，另一种类型标记了一种叫做组蛋白的蛋白质，DNA将其紧密地包裹起来，以适应细胞核。这些小的化学标签，或表观遗传/组蛋白修饰，允许组蛋白根据它们拥有的标签不同地发挥作用，通常是通过允许进入DNA和基因。重要的是，这使得相同的DNA序列能够以不同的方式表现，并提供了协调所有基因表达和响应不断变化的环境因素所需的灵活性。我们之前假设，蜂后和工蜂的不同饮食可以通过这些组蛋白决定不同的发育结果。通过之前BBSRC的资助，我们首次证明了蚁后和工蜂有自己特定的表观遗传组蛋白模式，即使它们的dna是相同的，这些差异与蚁后和工蜂特定的基因表达有关。出乎意料的是，我们还发现，一些最重要的表观遗传差异存在于蜜蜂基因组中不属于基因的区域，而这些非编码DNA区域可能对蜂王或工蜂的形成至关重要。为了确定这些区域是否对饮食敏感，我们将首先描述它们的特征，并确认它们是蜂后、工蜂和雄蜂发育的主要决定因素/调节因素。我们将通过在蜜蜂发育的早期阶段跟踪它们不断变化的表观遗传模式来确定它们是如何发挥作用的，并确定整个基因组中重要的差异在哪里。我们还将通过3D构象研究这些区域如何与蜜蜂基因组中的基因相互作用。然后，我们将能够确定女王饮食的一个重要组成部分是否可以直接改变这些区域的功能。我们将通过在实验室中培养单个蜜蜂幼虫，控制它们的饮食，并在分子水平和成年蜜蜂水平上监测对它们发育的影响，在那里我们可以寻找蜂王或工蜂的形态结构。这些实验将首次对蜜蜂的三种发育途径进行全面分析，并为理解营养如何塑造它们提供基础。

Honeybees are insect pollinators that are responsible for around 10% of the value of world food production. They live in complex societies comprising tens of thousands of individuals, most of these are female worker honeybees that are unable to reproduce and instead devote their short lives to finding food in flowers (nectar/pollen) and other tasks such as nursing larvae. In addition to these sterile female bees, the hive also contains male drones and a single female bee called the queen that has a much longer life span and can reproduce. The queen can lay fertilised or unfertilised eggs. Unfertilised eggs are fed drone jelly followed by nectar/pollen and become male drones, while fertilised eggs can become either queen or worker bees. Whether a fertilised egg results in a larva that will become an adult worker or queen bee depends on the type of food the larva is fed. Larvae destined to become workers are fed worker jelly followed by a diet of nectar/pollen and those destined to become queens are fed royal jelly. These differing diets are then maintained over the entire lifetime of the adult. The ability of an individual honeybee larva to become a queen, worker or drone cannot be because of different DNA: the genome of that larva has the capacity to become all three, it is due to the way genes are switched on or off in response to the specific diet; this determines such differing developmental outcomes. Epigenetics is a dynamic set of instructions that exist 'on top' of the genetic information, that can encode and direct multiple different outcomes from a fixed DNA sequence. There are two main families of epigenetic mechanisms; one type marks the actual DNA sequence, the other type marks proteins called histones that the DNA tightly wraps itself around in order to fit into the nucleus of a cell. These small chemical tags, or epigenetic/histone modifications, allow histones to act differently depending on which tags they have, usually by allowing access to the DNA and genes. Importantly, this enables identical DNA sequences to behave in different ways and provides the needed flexibility to coordinate the expression of all genes and respond to changing environmental factors.We previously hypothesised that the differing diets of queens and workers could determine alternative developmental outcomes via these histone proteins. Through previous BBSRC funding, we demonstrated for the first time that queens and workers have their own specific epigenetic histone patterns even though their DNAs are the same, and that these differences correlate with queen and worker -specific gene expression. Unexpectedly, we also found that some of the most important epigenetic differences were in regions of the honeybee genome that are not part of genes and that these non-coding regions of DNA may be crucial in making a queen or a worker. In order to determine if it is these regions that are sensitive to diet, we will first characterise them and confirm they are the main determinants/regulators of queen, worker and drone development. We will determine exactly how they function by following their changing epigenetic patterns through the early stages of honeybee development and identify where the important differences are across the entire genome. We will also look at how these regions interact with genes in the honeybee genome through 3D conformation. Then, we will be able to determine whether an important component of the queen diet can directly change the function of these regions. We will do this by growing individual bee larvae in the laboratory, manipulating their diets and monitoring the effects on their development at the molecular level and at the level of the adult bee, where we can look for queen or worker morphological structures. These experiments will produce the first comprehensive analyses of the three honeybee developmental pathways and also provide the basis for understanding how they are shaped by nutrition.