Ogihara Mari Horigane, Hikiba Juri, Suzuki Yutaka, Taylor DeMar, Kataoka Hiroshi
Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba, Japan.
Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan.
PLoS One. 2015 Apr 27;10(4):e0124953. doi: 10.1371/journal.pone.0124953. eCollection 2015.
Ecdysteroidogenesis is essential for arthropod development and reproduction. Although the importance of ecdysteroids has been demonstrated, there is little information on the sites and enzymes for synthesis of ecdysteroids from Chelicerates. Ecdysteroid functions have been well studied in the soft tick Ornithodoros moubata, making this species an excellent candidate for elucidating ecdysteroidogenesis in Chelicerates. Results showed that O. moubata has at least two ecdysteroidogenic enzymes, Spook (OmSpo) and Shade (OmShd). RNAi showed both enzymes were required for ecdysteroidogenesis. Enzymatic assays demonstrated OmShd has the conserved functions of ecdysone 20-hydroxylase. OmSpo showed specific expression in the ovaries of final nymphal and adult stages, indicating O. moubata utilizes the ovary as an ecdysteroidogenic tissue instead of specific tissues as seen in other arthropods. On the other hand, OmShd expression was observed in various tissues including the midgut, indicating functional ecdysteroids can be produced in these tissues. In nymphal stages, expression of both OmSpo and OmShd peaked before molting corresponding with high ecdysteroid titers in the hemolymph. In fed adult females, OmSpo expression peaked at 8-10 days after engorgement, while OmShd expression peaked immediately after engorgement. Mated females showed more frequent surges of OmShd than virgin females. These results indicate that the regulation of synthesis of ecdysteroids differs in nymphs and adult females, and mating modifies adult female ecdysteroidogenesis. This is the first report to focus on synthesis of ecdysteroids in ticks and provides essential knowledge for understanding the evolution of ecdysteroidogenesis in arthropods.
蜕皮甾体合成对于节肢动物的发育和繁殖至关重要。尽管蜕皮甾体的重要性已得到证实，但关于螯肢动物中蜕皮甾体合成的位点和酶的信息却很少。蜕皮甾体的功能在软蜱钝缘蜱中已得到充分研究，这使得该物种成为阐明螯肢动物蜕皮甾体合成的理想候选者。结果表明，钝缘蜱至少有两种蜕皮甾体生成酶，即幽灵蛋白（OmSpo）和阴影蛋白（OmShd）。RNA干扰表明这两种酶都是蜕皮甾体合成所必需的。酶活性测定表明，OmShd具有蜕皮激素20-羟化酶的保守功能。OmSpo在末龄若虫和成虫阶段的卵巢中特异性表达，这表明钝缘蜱利用卵巢作为蜕皮甾体生成组织，而不像其他节肢动物那样利用特定组织。另一方面，在包括中肠在内的各种组织中都观察到了OmShd的表达，这表明这些组织可以产生有功能的蜕皮甾体。在若虫阶段，OmSpo和OmShd的表达在蜕皮前达到峰值，这与血淋巴中高蜕皮甾体滴度相对应。在饱血的成年雌性中，OmSpo的表达在饱血后8-10天达到峰值，而OmShd的表达在饱血后立即达到峰值。交配的雌性比未交配的雌性显示出更频繁的OmShd激增。这些结果表明，若虫和成年雌性中蜕皮甾体合成的调节有所不同，交配会改变成年雌性的蜕皮甾体合成。这是第一份专注于蜱中蜕皮甾体合成的报告，为理解节肢动物蜕皮甾体合成的进化提供了重要知识。
