Department of Integrative Biology, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
Department of Biology, Kean University, Union, New Jersey, United States of America.
PLoS Biol. 2024 Aug 29;22(8):e3002771. doi: 10.1371/journal.pbio.3002771. eCollection 2024 Aug.
The chelicerate body plan is distinguished from other arthropod groups by its division of segments into 2 tagmata: the anterior prosoma ("cephalothorax") and the posterior opisthosoma ("abdomen"). Little is understood about the genetic mechanisms that establish the prosomal-opisthosomal (PO) boundary. To discover these mechanisms, we created high-quality genomic resources for the large-bodied spider Aphonopelma hentzi. We sequenced specific territories along the antero-posterior axis of developing embryos and applied differential gene expression analyses to identify putative regulators of regional identity. After bioinformatic screening for candidate genes that were consistently highly expressed in only 1 tagma (either the prosoma or the opisthosoma), we validated the function of highly ranked candidates in the tractable spider model Parasteatoda tepidariorum. Here, we show that an arthropod homolog of the Iroquois complex of homeobox genes is required for proper formation of the boundary between arachnid tagmata. The function of this homolog had not been previously characterized, because it was lost in the common ancestor of Pancrustacea, precluding its investigation in well-studied insect model organisms. Knockdown of the spider copy of this gene, which we designate as waist-less, in P. tepidariorum resulted in embryos with defects in the PO boundary, incurring discontinuous spider germ bands. We show that waist-less is required for proper specification of the segments that span the prosoma-opisthosoma boundary, which in adult spiders corresponds to the narrowed pedicel. Our results demonstrate the requirement of an ancient, taxon-restricted paralog for the establishment of the tagmatic boundary that defines Chelicerata.
螯肢动物的身体模式与其他节肢动物群体的区别在于其节段的划分，分为两个体区：前体部（“头胸部”）和后体部（“腹部”）。对于建立前体-后体（PO）边界的遗传机制知之甚少。为了发现这些机制，我们为大型蜘蛛 Aphonopelma hentzi 创建了高质量的基因组资源。我们沿着发育胚胎的前后轴对特定区域进行了测序，并应用差异基因表达分析来识别可能的区域身份调节因子。在生物信息学筛选出仅在 1 个体区（前体部或后体部）中高度表达的候选基因后，我们在易于处理的蜘蛛模型 Parasteatoda tepidariorum 中验证了高度排名候选基因的功能。在这里，我们表明，同源异形盒基因 Iroquois 复合物的节肢动物同源物对于蜘蛛类节肢动物体区边界的正确形成是必需的。这个同源物的功能以前没有被描述过，因为它在泛甲壳动物的共同祖先中丢失了，这使得它在研究得很好的昆虫模式生物中无法被研究。在 P. tepidariorum 中敲低这个基因的蜘蛛副本，我们将其命名为 waist-less，导致胚胎在 PO 边界处出现缺陷，产生不连续的蜘蛛生殖带。我们表明，waist-less 对于跨越前体-后体边界的节段的正确指定是必需的，在成年蜘蛛中，这对应于变窄的花梗。我们的结果表明，建立定义螯肢动物的体区边界需要一个古老的、分类限制的旁系同源物。
