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

蜜蜂是昆虫授粉者，占世界粮食产量的10%左右。它们生活在由成千上万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，而是将其短暂的生命用于在花朵中寻找食物（花蜜/花粉）和其他任务，如护理幼虫。除了这些不育的雌蜂，蜂巢还包含雄性雄蜂和一只被称为蜂王的雌蜂，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。未受精的卵被喂食雄蜂果冻，然后是花蜜/花粉，成为雄性雄蜂，而受精卵可以成为蜂王或工蜂。受精卵是否会产生幼虫，成为成年工蜂或蜂王取决于幼虫所喂养的食物类型。注定要成为工蜂的幼虫被喂食工蜂果冻，然后喂食花蜜/花粉，而那些注定要成为蜂王的幼虫则被喂食皇家果冻。这些不同的饮食，然后保持在整个成人的一生。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：该幼虫的基因组有能力成为所有三种，这是由于基因响应特定饮食的方式打开或关闭;这决定了这种不同的发育结果。表观遗传学是存在于遗传信息“之上”的一组动态指令，可以编码和指导来自固定DNA序列的多种不同结果。表观遗传机制有两个主要家族;一种类型标记实际的DNA序列，另一种类型标记称为组蛋白的蛋白质，DNA紧紧包裹在组蛋白周围，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所具有的标签而不同地发挥作用，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，并提供协调所有基因表达和应对不断变化的环境因素所需的灵活性。我们之前假设，蜂王和工蜂的不同饮食可以通过这些决定替代的发育结果组蛋白。通过之前的BBSRC资助，我们首次证明了蚁后和工蚁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，并且这些差异与蚁后和工蚁特异性基因表达相关。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，这些DNA的非编码区可能对制造蜂王或工蜂至关重要。为了确定这些区域是否对饮食敏感，我们将首先对它们进行定位，并确认它们是蜂王、工蜂和雄蜂发育的主要决定因素/调节因子。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的功能，并确定整个基因组中的重要差异。我们还将研究这些区域如何通过3D构象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来做到这一点，操纵它们的饮食，并在分子水平和成年蜜蜂的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。这些实验将首次全面分析蜜蜂的三种发育途径，并为理解它们是如何被营养塑造的提供基础。

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.