Department of Biochemistry, Virginia Tech, Blacksburg, VA 24061, USA.
Proc Natl Acad Sci U S A. 2011 Jan 11;108(2):638-43. doi: 10.1073/pnas.1013914108. Epub 2010 Dec 27.
Juvenile hormone (JH) plays crucial roles in many aspects of insect life. The Methoprene-tolerant (Met) gene product, a member of the bHLH-PAS family of transcriptional regulators, has been demonstrated to be a key component of the JH signaling pathway. However, the molecular function of Met in JH-induced signal transduction and gene regulation remains to be fully elucidated. Here we show that a transcriptional coactivator of the ecdysteroid receptor complex, FISC, acts as a functional partner of Met in mediating JH-induced gene expression. Met and FISC appear to use their PAS domains to form a dimer only in the presence of JH or JH analogs. In newly emerged adult female mosquitoes, expression of some JH responsive genes is considerably dampened when Met or FISC is depleted by RNAi. Met and FISC are found to be associated with the promoter of the early trypsin gene (AaET) when transcription of this gene is activated by JH. A juvenile hormone response element (JHRE) has been identified in the AaET upstream regulatory region and is bound in vitro by the Met-FISC complex present in the nuclear protein extracts of previtellogenic adult female mosquitoes. In addition, the Drosophila homologs of Met and FISC can also use this mosquito JHRE to activate gene transcription in response to JH in a cell transfection assay. Together, the evidence indicates that Met and FISC form a functional complex on the JHRE in the presence of JH and directly activate transcription of JH target genes.
保幼激素（JH）在昆虫生活的许多方面发挥着至关重要的作用。Methoprene-tolerant（Met）基因产物是转录调节因子 bHLH-PAS 家族的成员，已被证明是 JH 信号通路的关键组成部分。然而，Met 在 JH 诱导的信号转导和基因调控中的分子功能仍有待充分阐明。在这里，我们表明蜕皮甾类激素受体复合物的转录共激活因子 FISC，作为 Met 在介导 JH 诱导的基因表达中的功能伙伴。Met 和 FISC 似乎仅在存在 JH 或 JH 类似物的情况下才使用它们的 PAS 结构域形成二聚体。在新出现的成年雌性蚊子中，当 Met 或 FISC 通过 RNAi 耗尽时，一些 JH 反应基因的表达会显著减弱。当 JH 激活该基因的转录时，发现 Met 和 FISC 与早期胰蛋白酶基因（AaET）的启动子相关。在 AaET 上游调控区已经鉴定出一个保幼激素反应元件（JHRE），并且在来自预卵黄生成期成年雌性蚊子的核蛋白提取物中的 Met-FISC 复合物体外结合。此外，Met 和 FISC 的果蝇同源物也可以使用这种蚊子 JHRE 在细胞转染测定中响应 JH 激活基因转录。总之，这些证据表明，Met 和 FISC 在 JH 存在下形成 JHRE 上的功能性复合物，并直接激活 JH 靶基因的转录。
