Laboratory of Emerging Infectious Diseases, Department of Frontier Veterinary Medicine, Kagoshima University, 1-21-24 Korimoto, Kagoshima, Japan.
Int J Parasitol. 2012 Oct;42(11):991-8. doi: 10.1016/j.ijpara.2012.08.002. Epub 2012 Sep 15.
Vitellogenin (Vg) synthesis, vitellogenesis, is an essential process for the development and reproduction of ticks. Our previous finding led to the hypothesis that target of rapamycin (TOR) pathway is important for vitellogenesis in the hard tick, Haemaphysalis longicornis. The TOR pathway controls cellular activity according to nutrient availability in eukaryotes. TOR, a member of the phosphatidylinositol 3-kinase family, is a central player in this pathway. Here, we present preliminary evidence that H. longicornis TOR (HlTOR) controls vitellogenesis via activation of S6 kinase (S6K) in the fat body. RNA interference (RNAi)-mediated gene silencing of HlTOR was undertaken to elucidate the involvement of HlTOR in the vitellogenesis of the tick. HlTOR-RNAi caused inhibition of S6K phosphorylation in the fat body. HlTOR-RNAi also altered not only the expression levels of GATA mRNA and protein but also the intracellular localisation of GATA in the fat body. The expression levels of Vg mRNA and protein in the fat body of HlTOR-RNAi ticks were significantly lower than those in control ticks. In the pre-ovipositional stage, the ovaries of control ticks had brown oocytes developing, but those of HlTOR-RNAi ticks were white and immature. The haemolymph colour indicated that the amount of Vg was lower in HlTOR-RNAi ticks than in the controls. Furthermore, rapamycin inhibited S6K phosphorylation and reduced the expression levels of Vg mRNA and protein in the fat bodies. Vg proteins were not detected in rapamycin-treated fat bodies in the presence of 20-hydroxyecdysone. These results suggest that HlTOR activity is critical for vitellogenesis stimulated by 20-hydroxyecdysone.
卵黄蛋白原 (Vg) 的合成即卵黄发生，是蜱类发育和繁殖的必要过程。我们之前的研究结果表明，雷帕霉素靶蛋白 (TOR) 途径对于硬蜱长角血蜱的卵黄发生很重要。TOR 途径在真核生物中根据营养物质的可用性来控制细胞活性。TOR 是磷脂酰肌醇 3-激酶家族的成员，是该途径的核心分子。在这里，我们初步证明，长角血蜱 TOR (HlTOR) 通过脂肪体中的 S6 激酶 (S6K) 的激活来控制卵黄发生。采用 RNA 干扰 (RNAi) 介导的 HlTOR 基因沉默来阐明 HlTOR 在蜱的卵黄发生中的作用。HlTOR-RNAi 导致脂肪体中 S6K 磷酸化受到抑制。HlTOR-RNAi 还不仅改变了 GATA mRNA 和蛋白的表达水平，而且改变了 GATA 在脂肪体中的细胞内定位。HlTOR-RNAi 蜱的脂肪体中 Vg mRNA 和蛋白的表达水平明显低于对照蜱。在产卵前阶段，对照蜱的卵巢中有棕色卵母细胞发育，但 HlTOR-RNAi 蜱的卵巢呈白色且不成熟。血液颜色表明 HlTOR-RNAi 蜱的 Vg 量低于对照蜱。此外，雷帕霉素抑制 S6K 磷酸化并降低脂肪体中 Vg mRNA 和蛋白的表达水平。在存在 20-羟基蜕皮酮的情况下，雷帕霉素处理的脂肪体中未检测到 Vg 蛋白。这些结果表明，HlTOR 活性对于 20-羟基蜕皮酮刺激的卵黄发生至关重要。
