Abstract：
Exoskeletons are a defining character of all arthropods that provide physical support for their segmented bodies and appendages as well as protection from the environment and predation. This ubiquitous yet evolutionarily variable feature has been instrumental in facilitating the adoption of a variety of lifestyles and the exploitation of ecological niches across all environments. Throughout the radiation that produced the more than one million described modern species, adaptability afforded by segmentation and exoskeletons has led to a diversity that is unrivalled amongst animals. However, because of the limited extensibility of exoskeleton chitin and cuticle components, they must be periodically shed and replaced with new larger ones, notably to accommodate the growing individuals encased within. Therefore, arthropods grow discontinuously by undergoing periodic moulting events, which follow a series of steps from the preparatory pre-moult phase to ecdysis itself and post-moult maturation of new exoskeletons. Each event represents a particularly vulnerable period in an arthropod\'s life cycle, so processes must be tightly regulated and meticulously executed to ensure successful transitions for normal growth and development. Decades of research in representative arthropods provide a foundation of understanding of the mechanisms involved. Building on this, studies continue to develop and test hypotheses on the presence and function of molecular components, including neuropeptides, hormones, and receptors, as well as the so-called early, late, and fate genes, across arthropod diversity. Here, we review the literature to develop a comprehensive overview of the status of accumulated knowledge of the genetic toolkit governing arthropod moulting. From biosynthesis and regulation of ecdysteroid and sesquiterpenoid hormones, to factors involved in hormonal stimulation responses and exoskeleton remodelling, we identify commonalities and differences, as well as highlighting major knowledge gaps, across arthropod groups. We examine the available evidence supporting current models of how components operate together to prepare for, execute, and recover from ecdysis, comparing reports from Chelicerata, Myriapoda, Crustacea, and Hexapoda. Evidence is generally highly taxonomically imbalanced, with most reports based on insect study systems. Biases are also evident in research on different moulting phases and processes, with the early triggers and late effectors generally being the least well explored. Our synthesis contrasts knowledge based on reported observations with reasonably plausible assumptions given current taxonomic sampling, and exposes weak assumptions or major gaps that need addressing. Encouragingly, advances in genomics are driving a diversification of tractable study systems by facilitating the cataloguing of putative genetic toolkits in previously under-explored taxa. Analysis of genome and transcriptome data supported by experimental investigations have validated the presence of an \"ultra-conserved\" core of arthropod genes involved in moulting processes. The molecular machinery has likely evolved with elaborations on this conserved pathway backbone, but more taxonomic exploration is needed to characterise lineage-specific changes and novelties. Furthermore, linking these to transformative innovations in moulting processes across Arthropoda remains hampered by knowledge gaps and hypotheses based on untested assumptions. Promisingly however, emerging from the synthesis is a framework that highlights research avenues from the underlying genetics to the dynamic molecular biology through to the complex physiology of moulting.
摘要：
外骨骼是所有节肢动物的决定性特征，为其分段的身体和附属物提供物理支持，并保护环境和捕食。这种无处不在但进化可变的特征有助于促进各种生活方式的采用和在所有环境中开发生态位。在整个辐射中，产生了超过一百万个描述的现代物种，分割和外骨骼提供的适应性导致了动物之间无与伦比的多样性。然而,由于外骨骼甲壳素和角质层成分的延展性有限，它们必须定期脱落并用新的更大的替换，特别是为了适应包裹在里面的成长中的个体。因此,节肢动物通过经历周期性的换羽事件而不连续地生长，从准备的预蜕皮阶段到蜕皮本身以及新外骨骼的蜕皮后成熟遵循一系列步骤。每个事件都代表了节肢动物生命周期中的一个特别脆弱的时期，因此，必须严格监管和一丝不苟地执行过程，以确保正常生长和发育的成功过渡。对代表性节肢动物的数十年研究为理解所涉及的机制奠定了基础。在这个基础上，研究继续发展和测试有关分子组分的存在和功能的假设，包括神经肽,荷尔蒙，和受体，以及所谓的早期，迟到,和命运基因，跨节肢动物多样性。这里,我们回顾了文献，以全面概述控制节肢动物蜕皮的遗传工具包的积累知识的状况。从蜕皮类固醇和倍半萜类激素的生物合成和调节，涉及激素刺激反应和外骨骼重塑的因素，我们确定共性和差异，以及突出主要的知识差距，节肢动物群体。我们检查了支持当前模型的可用证据，这些模型是如何组件一起运行的，execute,从蜕皮中恢复过来，比较来自Chelicerata的报告，Myriapoda,甲壳动物,还有Hexapoda.证据通常在分类学上高度不平衡，大多数报告都是基于昆虫研究系统。在不同的换羽阶段和过程的研究中，偏见也很明显，早期触发因素和晚期效应因素通常是探索得最少的。我们的综合将基于报告的观察结果的知识与当前分类抽样的合理假设进行了对比，并暴露出薄弱的假设或需要解决的重大差距。令人鼓舞的是，基因组学的进步通过促进先前未充分探索的分类群中推定的遗传工具包的编目，推动了可处理的研究系统的多样化。通过实验研究支持的基因组和转录组数据的分析已经验证了参与蜕皮过程的节肢动物基因的“超保守”核心的存在。分子机制可能随着对这一保守途径骨架的阐述而进化，但是需要更多的分类学探索来描述谱系特定的变化和新颖性。此外，将这些与节肢动物蜕皮过程中的变革性创新联系起来，仍然受到基于未经检验的假设的知识差距和假设的阻碍。然而，有希望的是，从合成中脱颖而出的框架突出了从潜在遗传学到动态分子生物学再到复杂的蜕皮生理学的研究途径。
