Miura K, Zhu J, Dittmer N T, Chen L, Raikhel A S
Department of Medical Zoology, School of Medicine, Mie University, 2-174 Edobashi, Tsu 514-0001, Japan.
J Mol Endocrinol. 2002 Oct;29(2):223-38. doi: 10.1677/jme.0.0290223.
In the mosquito Aedes aegypti, vitellogenesis is activated via an ecdysteroid hormonal cascade initiated by a blood meal. The functional ecdysone receptor is a heterodimer composed of the ecdysone receptor (EcR) and ultraspiracle, the homolog of the retinoid X receptor. The precise tuning of this hormonal response requires participation of both positive and negative transcriptional regulators. In Drosophila, Svp, a homolog of chicken ovalbumin upstream promoter transcription factor (COUP-TF), inhibits ecdysone receptor complex-mediated transactivation in vitro and in vivo. Here we report the cloning and characterization of the Svp homolog in mosquito Aedes aegypti, AaSvp. It possesses a high degree of amino acid sequence similarity to the members of the COUP-TF/Svp subfamily. AaSvp transcripts and protein are present in the fat body at high levels from the state of arrest to about 60 h post blood meal. AaSvp binds strongly to a variety of direct repeats of the sequence AGGTCA, but weakly to inverted repeats such as hsp27 EcRE. Transient transfection assays in Drosophila S2 cells showed that AaSvp was able to repress 20-hydroxyecdysone (20E)-dependent transactivation mediated by the mosquito ecdysteroid receptor complex. These data suggest that AaSvp negatively regulates the 20E signaling in the fat body during mosquito vitellogenesis.
在埃及伊蚊中，卵黄生成是通过由血液摄取引发的蜕皮甾体激素级联反应来激活的。功能性蜕皮激素受体是一种异二聚体，由蜕皮激素受体（EcR）和超气门蛋白组成，超气门蛋白是类视黄醇X受体的同源物。这种激素反应的精确调节需要正、负转录调节因子的参与。在果蝇中，鸡卵清蛋白上游启动子转录因子（COUP-TF）的同源物Svp在体外和体内均可抑制蜕皮激素受体复合物介导的反式激活。在此，我们报告了埃及伊蚊中Svp同源物AaSvp的克隆和特性。它与COUP-TF/Svp亚家族成员具有高度的氨基酸序列相似性。从滞育状态到取食后约60小时，AaSvp转录本和蛋白在脂肪体中大量存在。AaSvp与序列AGGTCA的各种直接重复序列强烈结合，但与hsp27 EcRE等反向重复序列结合较弱。在果蝇S2细胞中进行的瞬时转染试验表明，AaSvp能够抑制由蚊子蜕皮甾体受体复合物介导的20-羟基蜕皮激素（20E）依赖性反式激活。这些数据表明，AaSvp在蚊子卵黄生成过程中对脂肪体中的20E信号传导起负调节作用。
