The early gene Broad is involved in the ecdysteroid hierarchy governing vitellogenesis of the mosquito Aedes aegypti
The early gene Broad is involved in the ecdysteroid hierarchy governing vitellogenesis of the mosquito Aedes aegypti
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DOI：
10.1677/jme.1.01531
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发表时间：
2004-12-01
影响因子：
3.5
通讯作者：
Raikhel, AS
中科院分区：
文献类型：
--
作者：
Chen, L;Zhu, J;Raikhel, AS
BR基因编码一个C2H2型锌指DNA结合蛋白家族，在果蝇、黑腹果蝇和夜蛾中是20-羟基蜕皮酮(20E)调控体系中的重要成员。在这项研究中，我们已经证明了br基因参与了控制埃及伊蚊卵黄生成的20E-调控体系。与E74和E75早期基因不同，br的表达在发病前期的雌性中被激活，在保幼激素(JH)依赖期。在体外暴露于JH III后，2日龄雌性脂肪体中Z1、Z2和Z4亚型的mRNA水平升高，但JH III抑制了3日龄至5日龄雌性BR的20E激活，表明激素承诺发生了变化。采血后Z1、Z2和Z4在卵黄生成组织、脂肪体和卵巢均有表达，与蜕皮类固醇滴度峰值相对应。在脂肪体中，这三种异构体的mRNA谱与卵黄蛋白前体(YPP)基因的谱有很好的相关性。这些BR亚型在体外培养的脂肪体中被20E激活，表现为早期基因，具有自我抑制的自我调节环，可被蛋白抑制剂环己胺阻断。在YPP主要基因卵黄蛋白原(VG)的5‘-调控区，所有四种BR亚型都存在多个结合位点。BR亚型对VG表达的影响已通过细胞转染分析得到证实。特别是，BR亚型本身对VG启动子没有影响。然而，Z1和Z4分别抑制埃及伊蚊蜕皮激素受体(ECR)/超阿司匹林(USP)介导的VG启动子的20E激活，而Z2在20E存在的情况下增强AaEcR/AaUSP对VG启动子的激活。在同一实验中，Z3的作用不明显。这些结果表明，BR亚型对于VG基因对20E的正确激活和终止是必不可少的。总体而言，我们的研究表明br参与了蚊子卵黄发生的调控。
The broad (br) gene, encoding a family of C2H2 type zinc-finger DNA-binding proteins, has been shown to act as a crucial member of the 20-hydroxyecdysone (20E) regulatory hierarchy in the fruitfly, Drosophila melanogaster and the moth, Manduca sexta. In this study, we have shown that the br gene is involved in the 20E-regulatory hierarchy controlling vitellogenesis in the mosquito, Aedes aegypti. Unlike E74 and E75 early genes, expression of br was activated in previtellogenic females, during a juvenile hormone (JH)-dependent period. The levels of Z1, Z2 and Z4 isoform mRNA were elevated in the fat body of 2-day-old females after in vitro exposure to JH III. However, JH III repressed 20E activation of br in 3- to 5-day-old females, indicating a switch in hormonal commitment. Expression of Z1, Z2 and Z4 was stimulated after blood feeding in both vitellogenic tissues, the fat body and the ovary, corresponding to peaks of ecdysteroid titers. In the fat body, the mRNA profiles of these three isoforms correlated well with those of yolk protein precursor (YPP) genes. These BR isoforms were activated by 20E in fat bodies cultured in vitro and behaved as early genes, with a self-repressive autoregulatory loop that can be blocked by the protein inhibitor, cyclohexamide. Multiple binding sites for all four BR isoforms were present in the 5'-regulatory region of the major YPP gene, vitellogenin (Vg). Effects of BR isoforms on the expression of Vg have been demonstrated by cell transfection analysis. In particular, BR isoforms by themselves had no effects on the Vg promoter. However, Z1 and Z4 each repressed Aedes aegypti ecdysone receptor (EcR)/Ultraspiracle (USP)-mediated 20E activation of the Vg promoter, while Z2 enhanced activation of the Vg promoter by AaEcR/AaUSP in the presence of 20E. Z3 had no obvious effect in the same experiment. These results suggested that BR isoforms are essential for proper activation and termination of the Vg gene in response to 20E. Overall, our study implicated br in the regulation of mosquito vitellogenesis.