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 Mar;94:50-60. doi: 10.1016/j.ibmb.2017.09.012. Epub 2017 Sep 22.
Hormone receptor 4 (HR4) is involved in the regulation of 20-hydroxyecdysone (20E) biosynthesis and the mediation of 20E signaling during larval-pupal transition in a holometabolan Drosophila melanogaster, whereas it acts as a repressor in 20E-responsive transcriptional cascade in a hemimetabolan, Blattella germanica. Here we characterized two HR4 splicing variants, LdHR4X1 and LdHR4X2, in a coleopteran Leptinotarsa decemlineata. LdHR4X1 was highly expressed in the prothoracic gland and epidermis while LdHR4X2 was abundantly transcribed in the nervous system. In vivo results showed that both prothoracicotropic hormone and 20E pathways transcriptionally regulated LdHR4, in an isoform-dependent pattern. RNA interference of LdHR4 at the final (fourth) larval instar, in contrast to the second- and third-instar periods, enhanced the expression of two ecdysteroidogenesis genes, increased 20E titer, upregulated transcription of five 20E-response genes, and reduced the mRNA level of Fushi tarazu-factor 1 (FTZ-F1). As a result, the fourth-instar LdHR4 RNAi larvae exhibited accelerated development and reduced body weight. Moreover, knockdown of LdHR4 at the fourth instar resulted in larval lethality and impaired pupation. Feeding of pyriproxyfen (a mimic of juvenile hormone) or silencing of a juvenile hormone degrading enzyme gene restored the normal course of ecdysteroidogenesis, duration of larval development, and body weight in fourth-instar LdHR4 RNAi larvae. The treatment partially suppressed the larval mortality but not the failure to pupate. The dual role of HR4 during larval-pupal metamorphosis appears to be evolutionarily conserved among holometabolans.
激素受体 4 (HR4) 参与调控蜕皮甾酮（20E）生物合成，并在果蝇（Drosophila melanogaster）的幼虫-蛹转变过程中介导 20E 信号，而在半变态昆虫德国小蠊（Blattella germanica）中，它作为 20E 反应性转录级联的阻遏物发挥作用。在此，我们在鞘翅目昆虫暗黑鳃金龟（Leptinotarsa decemlineata）中鉴定了两种 HR4 剪接变体，LdHR4X1 和 LdHR4X2。LdHR4X1 在前胸腺和表皮中高度表达，而 LdHR4X2 在神经系统中大量转录。体内结果表明，前胸腺激素和 20E 途径都以依赖于同工型的方式转录调控 LdHR4。与第二和第三龄期相比，在最后（第四）龄幼虫期干扰 LdHR4，会增强两种蜕皮甾酮生成基因的表达，增加 20E 滴度，上调五个 20E 反应基因的转录，并降低 Fushi tarazu-factor 1 (FTZ-F1) 的 mRNA 水平。结果，第四龄幼虫 LdHR4 RNAi 增强了发育速度并降低了体重。此外，在第四龄期干扰 LdHR4 会导致幼虫死亡和蛹化受损。喂食吡虫威（保幼激素类似物）或沉默一个保幼激素降解酶基因，可以恢复第四龄幼虫 LdHR4 RNAi 中正常的蜕皮甾酮生成、幼虫发育时间和体重。该处理部分抑制了幼虫死亡率，但未能抑制蛹化失败。HR4 在幼虫-蛹变态过程中的双重作用似乎在完全变态昆虫中是保守的。
