Genetic and Molecular Regulation of Beak Tip (Rhinotheca) Shape in Layer Hens

喙是一个复杂的器官，形状和大小变化很大。鸡喙是由两块骨头组成的，上面覆盖着一层角蛋白（构成毛发、指甲、羽毛、爪子和喙的蛋白质）。喙为产蛋鸡提供了进食、饮水和探索环境的手段。它也能够对其他母鸡造成伤害，这种有害的行为被称为伤害性啄食。伤害性啄食对母鸡的福利和生产构成了严重的挑战，特别是在非笼养鸡群中，其患病率可达80%。伤害性啄食的爆发可能导致同类相食和死亡，在极端情况下死亡率为50%或更高。尽管近几十年来在管理方面取得了进展，但啄禽疫情仍然无法得到可靠的控制或预防。喙修剪是减少啄相关损害的最有效方法;然而，这种做法也带来了自己的福利问题。这导致许多国家禁止修剪鸟嘴。在英国，2016年曾考虑过一项禁令，但被拒绝了;然而，DEFRA的目标是“尽快合理地停止例行的喙修剪。为了实现这一点，需要尽一切努力减少有害的啄。“为了实现可持续的解决方案，需要采取多因素方法。在改善鸟类管理以尽量减少未修剪喙的鸟群中的疫情方面取得了一些成功。通过遗传选择不太倾向于参与该行为的产蛋鸡，在减少IP发生率方面也取得了成功。这项工作提出了一个不同的方向，以补充这些努力。最近的研究表明，喙本身可以作为一种工具，以减少啄相关的损害，并提高成功地住房非喙处理蛋鸡的机会。我们的研究小组已经开发并发表了识别喙形状的方法，并发现遗传层线内部和之间存在很大的差异，表现为尖锐度，角度和整体喙大小。除了这些形状和大小的外部测量，使用喙作为减少损伤的工具还需要详细了解喙在胚胎中是如何发育的，以及它的形状是如何确定的。目前，还不完全了解远喙尖（喙鞘）是如何发育的。也就是说，构成鼻鞘的细胞在细胞命运、分子身份和蛋白质组成方面是否有专门化？我们的总体目标是通过包括选择和基因编辑在内的遗传干预，实现商业规模的喙形修改。我们的目标是通过建立两组具有相反喙形状的蛋鸡来实现这一点。在使用机器学习对鸟类的喙进行成像和分类后，鸟类将被分组。每组的育种对将用于胚胎生产。来自这些组的胚胎将进行组织学和原位杂交，以详细描述在角化前细胞分化的变化。使用罗斯林研究所的专门鸟类品系，将创建命运图（用于研究组织的胚胎起源），以确定有助于喙尖的细胞来自何处。最后，了解囊膜细胞的起源并使用繁殖组胚胎，我们将创建一个体外角质形成细胞模型，以探索遗传和传递的扰动如何改变这些专门细胞的蛋白质生产。这将能够测试与喙发育和组成相关的遗传变异。这一努力的成功需要了解的遗传，分子和细胞的决定因素，以避免损害喙功能和其他多效性的影响。通过了解在分子水平上控制鸡喙形状的因素，我们获得了知识和工具，这些知识和工具可能导致能够预测和/或操纵基因组中的变化如何改变鸡喙形状。在未来，新的育种技术可以利用这些知识。

The beak is a complex organ that varies considerably in shape and size. Chicken beaks are formed of two bones covered by a layer of keratin (protein that makes up hair, nails, feathers, claws, and beaks). The beak provides laying hens with the means to eat, drink, and explore their environment. It is also capable of inflicting injury on other hens, a harmful behaviour known as injurious pecking. Injurious pecking poses a serious challenge to hen welfare and production, particularly in non-cage flocks where its prevalence can reach 80%. Outbreaks of injurious pecking can result in cannibalism and death, with 50% mortality or more in extreme cases. Despite the advancements in management made in recent decades, pecking outbreaks still cannot be reliably controlled or prevented. Beak trimming is the most effective method of reducing pecking-related damage; however, the practice raises its own welfare issues. This has led to beak trimming bans in numerous countries. In the UK, a ban was considered in 2016 and declined; however, DEFRA aims "to stop routine beak trimming as soon as reasonably possible. To achieve this, every effort is needed to reduce injurious pecking." To move towards a sustainable solution, a multifactorial approach is needed. There has been some success in improving bird management to minimise outbreaks in non-beak trimmed flocks. There has also been success in reducing the incidence of IP by genetically selecting laying hens that are less apt to engage in the behaviour. This work proposes a different direction to supplement these efforts. Recent research suggests that the beak itself can be a tool to reduce pecking-related damage and improve the chances of successfully housing non-beak treated laying hens. Our research group has developed and published methods to identify beak shapes and found large variation within and between genetic layer lines, manifesting as pointedness, angle, and overall beak size. Beyond these external measures of shape and size, using the beak as a tool to reduce damage requires a detailed understanding of how the beak develops within the embryo and how its shape is determined. Presently, it is not fully understood how the distal beak tip (rhinotheca) develops. Namely, are the cells that make up the rhinotheca specialised with respect to cellular fate, molecular identity, and protein composition? Our overall goal is to enable beak shape modification at a commercial scale through genetic interventions including selection and gene editing. We aim to do this by establishing two groups of laying hens with opposing beak shapes. Birds will be placed into groups after their beaks are imaged and categorised using machine learning. Breeding pairs from each group will be used for embryo production. The embryos from these groups will undergo histology and in situ hybridisation to detail changes of cell differentiation that precede rhinotheca keratinisation. Using specialised avian lines from the Roslin Institute, fate maps (used to study embryonic origins of tissues) will be created to establish where the cells that contribute to the beak tip originate from. Finally, understanding where the rhinotheca cells originate and using the breeding group embryos, we will create an in vitro keratinocyte model to explore how perturbations, genetic and delivered, alter these specialised cells' protein production. This will enable testing of genetic variants relevant to beak development and composition. Success in this endeavour requires understanding the genetic, molecular, and cellular determinants of rhinotheca shape to avoid compromising beak function and other pleiotropic effects. By understanding factors that control beak shape at the molecular level, we gain knowledge and tools that may lead to being able to predict and/or manipulate how changes in the genome alter chicken beak shape. In the future, new breeding technologies could capitalise on this knowledge.