Laboratory of Evolutionary Cell and Developmental Biology, JT Biohistory Research Hall, 1-1 Murasaki-cho, Takatsuki, Osaka, 569-1125, Japan.
Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka, Japan.
Dev Genes Evol. 2020 Mar;230(2):49-63. doi: 10.1007/s00427-019-00631-x. Epub 2019 Apr 10.
Bilaterally symmetric body plans of vertebrates and arthropods are defined by a single set of two orthogonal axes, the anterior-posterior (or head-tail) and dorsal-ventral axes. In vertebrates, and especially amphibians, complete or partial doubling of the bilaterian body axes can be induced by two different types of embryological manipulations: transplantation of an organizer region or bi-sectioning of an embryo. Such axis doubling relies on the ability of embryonic fields to flexibly respond to the situation and self-regulate toward forming a whole body. This phenomenon has facilitated experimental efforts to investigate the mechanisms of vertebrate body axes formation. However, few studies have addressed the self-regulatory capabilities of embryonic fields associated with body axes formation in non-vertebrate bilaterians. The pioneer spider embryologist Åke Holm reported twinning of spider embryos induced by both types of embryological manipulations in 1952; yet, his experiments have not been replicated by other investigators, and access to spider or non-vertebrate twins has been limited. In this review, we provide a historical background on twinning experiments in spiders, and an overview of current twinning approaches in familiar spider species and related molecular studies. Moreover, we discuss the benefits of the spider model system for a deeper understanding of the ancestral mechanisms of body axes formation in arthropods, as well as in bilaterians.
两侧对称的脊椎动物和节肢动物的身体模式由一组两个正交轴定义，即前后（或头尾）轴和背腹轴。在脊椎动物中，特别是在两栖动物中，可以通过两种不同类型的胚胎操作来诱导双边身体轴的完全或部分加倍：组织者区域的移植或胚胎的二分。这种轴加倍依赖于胚胎场能够灵活地响应情况并自我调节形成整个身体的能力。这种现象促进了实验努力，以研究脊椎动物身体轴形成的机制。然而，很少有研究涉及与非脊椎动物双边动物身体轴形成相关的胚胎场的自我调节能力。先驱蜘蛛胚胎学家Åke Holm 于 1952 年报告了两种类型的胚胎操作诱导的蜘蛛胚胎的孪生；然而，他的实验并没有被其他研究人员复制，而且蜘蛛或非脊椎动物双胞胎的获取受到限制。在这篇综述中，我们提供了蜘蛛孪生实验的历史背景，以及在常见蜘蛛物种和相关分子研究中当前的孪生方法概述。此外，我们讨论了蜘蛛模型系统的好处，以更深入地了解节肢动物以及双边动物身体轴形成的祖先机制。
