Lin Xianyu, Yu Na, Smagghe Guy
Department of Crop Protection, Ghent University, 9000 Ghent, Belgium.
Department of Crop Protection, Ghent University, 9000 Ghent, Belgium.
Gen Comp Endocrinol. 2018 Mar 1;258:149-156. doi: 10.1016/j.ygcen.2017.05.012. Epub 2017 May 16.
The steroid hormone 20-hydroxyecdysone (20E), the major developmental hormone in insects, controls all the developmental transitions including ecdysis and metamorphosis. In our study with last larval stages of the red flour beetle, Tribolium castaneum, dsRNA-mediated gene silencing of Forkhead box protein O (FoxO) resulted in reduced food intake and larval mass and this agreed with a reduction in the expression of insulin signaling-related genes (insulin-like peptides 2, 3, 4, and chico). Interestingly, we also observed a significant delay in the moment of the pupation and these FoxO-silenced larvae then turned brown at the middle pupal stage followed by death. The observed delay of pupation concurred with a significant delay in 20E titer in dsFoxO-injected larvae and this in turn agreed with a significant delay in expression of prothoracicotropic hormone (ptth) that is a gene stimulating ecdysteroid biosynthesis, and of spook (spo) that is one of the early Halloween genes involved in ecdysteroid biosynthesis. In addition, there was also a delayed expression of the ecdysteroid response gene hormone receptor 3 (HR3). In an attempt to rescue the effects by dsFoxO, injection of 20E into T. castaneum larvae stimulated the expression of HR3 and induced one extra larval-larval molt, confirming the responsiveness for ecdysteroid signaling in dsFoxO-injected larvae. The observations of this project suggest that FoxO is a player in the timing of pupation via the regulating of ecdysteroid biosynthesis, together with the regulation of both insulin signaling and nutrition.
类固醇激素20-羟基蜕皮酮（20E）是昆虫主要的发育激素，控制着包括蜕皮和变态在内的所有发育转变。在我们对赤拟谷盗最后幼虫阶段的研究中，双链RNA介导的叉头框蛋白O（FoxO）基因沉默导致食物摄入量和幼虫体重降低，这与胰岛素信号相关基因（胰岛素样肽2、3、4和chico）表达的降低一致。有趣的是，我们还观察到化蛹时刻显著延迟，这些FoxO沉默的幼虫在蛹中期变成褐色，随后死亡。观察到的化蛹延迟与注射dsFoxO的幼虫中20E滴度的显著延迟一致，这反过来又与促前胸腺激素（ptth）的表达显著延迟一致，ptth是一种刺激蜕皮甾体生物合成的基因，而spook（spo）是参与蜕皮甾体生物合成的早期万圣节基因之一。此外，蜕皮甾体反应基因激素受体3（HR3）的表达也延迟了。为了挽救dsFoxO的影响，向赤拟谷盗幼虫注射20E刺激了HR3的表达，并诱导了一次额外的幼虫-幼虫蜕皮，证实了注射dsFoxO的幼虫对蜕皮甾体信号的反应性。该项目的观察结果表明，FoxO通过调节蜕皮甾体生物合成以及胰岛素信号和营养，在化蛹时间中发挥作用。
