Education Ministry Key Laboratory of Integrated Management of Crop Diseases and Pests, College of Plant Protection, Nanjing Agricultural University, Nanjing, 210095, China.
Department of Plant Protection, Xinjiang Academy of Agricultural Sciences, Urumqi, 830091, China.
Insect Biochem Mol Biol. 2018 Dec;103:1-11. doi: 10.1016/j.ibmb.2018.10.001. Epub 2018 Oct 6.
It is noted that insect insulin/insulin-like growth factor/target of rapamycin signaling is critical for the regulation of metamorphosis in holometabolous insects. However, the molecular mechanism remains undetermined. Our previous findings reveal that RNA interference (RNAi)-mediated knockdown of an insulin gene (LdILP2) in Leptinotarsa decemlineata disturbs both 20-hydroxyecdysone (20E) and juvenile hormone (JH) signaling, and impairs pupation. In the present paper, we further observed that the expression of the insulin receptor substrate gene chico (Ldchico) and the phosphoinositide-3-kinase gene pi3k (Ldpi3k92E) was repressed in LdILP2 depleted larvae. Moreover, RNAi of Ldchico or Ldpi3k92E decreased food consumption, affected absorption and metabolism of amino acids and sugars, and reduced expression of several 20E (LdEcR, LdHR3 and LdE75) and JH (LdJHAMT, LdKr-h1 and LdHairy) signaling genes. As a result, larval development was postponed and larval growth was inhibited. Intriguingly, knockdown of Ldchico, rather than Ldpi3k92E, impaired larval-pupal and pupal-adult ecdysis, and specifically repressed transcription of another 20E signaling gene LdUSP. Ingestion of 20E rescued the expression of LdEcR, LdHR3 and LdE75, whereas 20E feeding restored neither the decreased LdUSP mRNA level, nor the reduced pupation and adult emergence rates in Ldchico RNAi larvae. Therefore, Chico is critical for the regulation of larval-pupal-adult transition by a PI3K-independent pathway, perhaps through activation of USP in L. decemlineata.
据指出，昆虫胰岛素/胰岛素样生长因子/雷帕霉素靶蛋白信号对于完全变态昆虫的变态调节至关重要。然而，其分子机制仍未确定。我们之前的研究结果表明，在马铃薯甲虫（Leptinotarsa decemlineata）中，通过 RNA 干扰（RNAi）敲低胰岛素基因（LdILP2）会扰乱 20-羟基蜕皮酮（20E）和保幼激素（JH）信号，并损害化蛹。在本论文中，我们进一步观察到胰岛素受体底物基因 chico（Ldchico）和磷酸肌醇 3-激酶基因 pi3k（Ldpi3k92E）在 LdILP2 耗尽的幼虫中表达受到抑制。此外，Ldchico 或 Ldpi3k92E 的 RNAi 降低了食物消耗，影响了氨基酸和糖的吸收和代谢，并降低了几个 20E（LdEcR、LdHR3 和 LdE75）和 JH（LdJHAMT、LdKr-h1 和 LdHairy）信号基因的表达。结果，幼虫发育被推迟，幼虫生长受到抑制。有趣的是，敲低 Ldchico，而不是 Ldpi3k92E，损害了幼虫-蛹和蛹-成虫蜕皮，并特异性抑制了另一个 20E 信号基因 LdUSP 的转录。摄入 20E 可挽救 LdEcR、LdHR3 和 LdE75 的表达，而 20E 喂养既不能恢复 Ldchico RNAi 幼虫中降低的 LdUSP mRNA 水平，也不能恢复降低的化蛹率和成虫羽化率。因此，Chico 通过在 L. decemlineata 中激活 USP，在由 PI3K 独立途径调节幼虫-蛹-成虫转变中是至关重要的。
