Gainett Guilherme, Sharma Prashant P
Department of Integrative Biology, University of Wisconsin-Madison, Madison, WI 53706 USA.
Evodevo. 2020 Aug 28;11:18. doi: 10.1186/s13227-020-00163-w. eCollection 2020.
The resurgence of interest in the comparative developmental study of chelicerates has led to important insights, such as the discovery of a genome duplication shared by spiders and scorpions, inferred to have occurred in the most recent common ancestor of Arachnopulmonata (a clade comprising the five arachnid orders that bear book lungs). Nonetheless, several arachnid groups remain understudied in the context of development and genomics, such as the order Amblypygi (whip spiders). The phylogenetic position of Amblypygi in Arachnopulmonata posits them as an interesting group to test the incidence of the proposed genome duplication in the common ancestor of Arachnopulmonata, as well as the degree of retention of duplicates over 450 Myr. Moreover, whip spiders have their first pair of walking legs elongated and modified into sensory appendages (a convergence with the antennae of mandibulates), but the genetic patterning of these antenniform legs has never been investigated.
We established genomic resources and protocols for cultivation of embryos and gene expression assays by in situ hybridization to study the development of the whip spider . Using embryonic transcriptomes from three species of Amblypygi, we show that the ancestral whip spider exhibited duplications of all ten Hox genes. We deploy these resources to show that paralogs of the leg gap genes and retain arachnopulmonate-specific expression patterns in . We characterize the expression of leg gap genes -, - and - in the embryonic antenniform leg and other appendages, and provide evidence that allometry, and by extension the antenniform leg fate, is specified early in embryogenesis.
This study is the first step in establishing as a chelicerate model for modern evolutionary developmental study, and provides the first resources sampling whip spiders for comparative genomics. Our results suggest that Amblypygi share a genome duplication with spiders and scorpions, and set up a framework to study the genetic specification of antenniform legs. Future efforts to study whip spider development must emphasize the development of tools for functional experiments in .
对螯肢动物比较发育研究兴趣的复苏带来了重要见解，比如发现蜘蛛和蝎子共享一次基因组复制事件，据推测该事件发生在蛛形肺亚纲（一个包含五个具有书肺的蛛形纲目动物的进化枝）的最近共同祖先中。尽管如此，在发育和基因组学背景下，仍有几个蛛形纲类群研究不足，比如无鞭目（鞭蛛）。无鞭目在蛛形肺亚纲中的系统发育位置使其成为一个有趣的类群，可用于检验蛛形肺亚纲共同祖先中所提出的基因组复制事件的发生率，以及4.5亿年里重复基因的保留程度。此外，鞭蛛的第一对步足延长并特化为感觉附肢（这与有颚类的触角趋同），但这些触角状腿的遗传模式从未被研究过。
我们建立了基因组资源以及胚胎培养和基因表达原位杂交检测的方案，以研究鞭蛛的发育。利用三种无鞭目的胚胎转录组，我们表明，原始鞭蛛表现出所有十个Hox基因的复制。我们利用这些资源表明，腿部间隙基因 和 的旁系同源基因在 中保留了蛛形肺亚纲特有的表达模式。我们描述了腿部间隙基因 -、 - 和 - 在胚胎触角状腿及其他附肢中的表达，并提供证据表明异速生长以及由此延伸出的触角状腿的命运在胚胎发育早期就已确定。
本研究是将 确立为现代进化发育研究的螯肢动物模型的第一步，并提供了首个用于比较基因组学的鞭蛛样本资源。我们的结果表明，无鞭目与蜘蛛和蝎子共享一次基因组复制事件，并建立了一个研究触角状腿遗传特化的框架。未来研究鞭蛛发育的工作必须强调开发用于 功能实验的工具。
