Defining mechanisms of mucosal innate defence using the X. tropicalis tadpole

病原体是引起疾病的微生物和病毒，对动物的健康和生存构成严重挑战。当动物死于传染病时，这是因为病原体破坏了人体的自然防御机制。总的来说，这些防御分为两种类型，先天和适应性免疫防御。适应性免疫是一种特异性防御，针对特定病原体产生的抗体被用来快速应对感染。然而，如果病原体从一开始就没有机会感染人体，这对动物是有利的。先天免疫（非特异性免疫）是抵御感染的第一道防线，包括产生进入的物理障碍和产生主动摧毁病原体的分子。身体中暴露的组织（如肺和肠道）使用的这样一种物理屏障是粘液层的产生。粘液会捕获病原体，阻止它们进入潜在的细胞，还含有其他天然防御分子，如抗菌剂。研究黏液是很重要的，可以了解它是如何运作的，以及当它功能失调和被破坏时会发生什么。由于缺乏正常运作的粘液屏障，可能会出现严重疾病；这些疾病包括炎症性肠病、胃溃疡和哮喘。哺乳动物模型，包括老鼠，经常被用来研究肺和肠道中的粘液。然而，简单的非哺乳动物生物也可以为粘液功能的进化保守机制提供有价值的见解。在本文中，我们以热带爪蟾（Xenopus tropicalis）为研究对象，特别是蝌蚪期体表黏液作为研究先天防御的模型。热带生物是一种模式生物，通常用于发育生物学，以了解胚胎发育的基本概念和发生的分子过程。近年来，我们一直在研究胚胎在发育成蝌蚪和青蛙之前，胚胎皮肤是如何变化的。我们已经在蝌蚪的皮肤中发现了许多类型的细胞，包括两种类型的分泌细胞，它们一起分泌分子，形成皮肤表面的黏液层。我们建议这个简单的模型可以用于研究粘膜先天防御的各个方面，这将适用于其他生物，包括人类。事实上，我们已经在蝌蚪粘液中发现了许多已知的人类同源的先天防御分子，但它们的功能在很大程度上尚未被探索。在这项拨款提案中，我们打算通过一些手段来审视它们的职能。热带蝌蚪模型有一些明显的优势，因为皮肤直接面对环境，因此可以改变条件来观察效果。哺乳动物的粘液屏障则不是这样，粘液屏障通常存在于体内的组织中，因此更难进入。此外，热带棘猴蝌蚪尚未获得适应性免疫（这发生在它们发育的后期），因此任何观察到的影响将是由于先天防御机制，而不是更复杂的，对感染的综合适应性反应。我们打算从基因上改变蝌蚪皮肤黏液层中先天防御分子的表达，然后用在其原生环境中发现的潜在病原体（细菌，嗜水气单胞菌）挑战蝌蚪，以了解每种分子的重要性。我们将研究它们在物理屏障中的结构作用以及它们作为抗微生物剂的潜在功能作用。我们的目标是推进蝌蚪如何保护自己免受感染的理解，并最终进化保守的先天防御机制如何在粘液屏障中发挥作用。这可能会带来治疗疾病的新靶点。

Pathogens are disease causing microorganisms and viruses, which represent a severe challenge to the health and survival of animals. When animals succumb to infectious disease, it is because pathogens have breached the body's natural defence mechanisms. Broadly, these defences fall into two types, innate and adaptive immune defences. Adaptive immunity is a specific defence, where antibodies generated against a particular pathogen are used to rapidly respond to infection. However, it is advantageous for animals if pathogens never have the opportunity to infect the body in the first place. Innate immunity (non-specific immunity) is the first line of defence against infection and includes the generation of physical barriers to entry and the production of molecules that actively destroy pathogens. One such physical barrier used by exposed tissues in the body (e.g. lungs and gut) is the production of a mucus layer. Mucus traps pathogens preventing them from accessing the underlying cells and also contains other innate defence molecules such as antibacterial agents. It is important to study mucus to understand how it functions and what happens when it becomes dysfunctional, and is breached. Severe diseases can arise due to lack of a properly functioning mucus barrier; these include inflammatory bowel disease, stomach ulcers, and asthma. Mammalian models, including mice, are often used to study mucus in the lungs and gut. However, simple non-mammalian organisms can also provide valuable insight into evolutionarily conserved mechanisms of mucus function. In this proposal, we introduce the frog, Xenopus tropicalis, and specifically the mucus on the surface of the tadpole stage, as a model to study innate defence.X. tropicalis is a model organism commonly used in developmental biology to understand basic concepts in how embryos develop and the molecular processes that occur. In recent years, we have been studying how the embryonic skin changes as the embryo develops into a tadpole, prior to becoming a frog. We have identified a number of cell types in the tadpole skin, including two types of secretory cells that together secrete molecules that form a mucus layer over the surface of the skin. We are proposing that this simple model can be used to study aspects of mucosal innate defence that will be applicable to other organisms, including humans. Indeed, we have identified a number of innate defence molecules in the tadpole mucus that have known homologues in humans and yet their functions are largely unexplored. In this grant proposal, we intend to interrogate their functions through a number of means. The X. tropicalis tadpole model has some distinct advantages in that the skin directly faces the environment and so conditions can be altered to observe the effects. This is not the case with mammalian mucus barriers, which are usually found on tissues within the body and are thus more difficult to access. In addition, X. tropicalis tadpoles have yet to acquire adaptive immunity (which happens later in their development) so any observed effects will be due to innate defence mechanisms, rather than a more complicated, combined adaptive response to infection. We intend to genetically alter the expression of the innate defence molecules in the tadpoles skin mucus layer and then challenge the tadpoles with a potential pathogen found in their native environment (the bacterium, Aeromonas hydrophila), in order to understand the importance of each molecule. We will look at their structural roles in the physical barrier and their potential functional roles as anti-microbial agents. We aim to advance the understanding of how the tadpole defends itself against infection and ultimately how evolutionarily conserved innate defence mechanisms function in mucus barriers. This could potentially lead to new targets for treating disease.