七星瓢虫卵黄原蛋白基因的表达:保幼激素类似物对mRNA的诱导

在七星瓢虫(Coccinella septempunctata)中,保幼激素调控脂肪体中卵黄原蛋白基因的表达。蛋白质合成实验证明,保幼激素类似物大幅度地促进取食人工饲料的雌虫脂肪体中卵黄原蛋白的合成。保幼激素类似物的作用有高度选择性,使卵黄原蛋白占总蛋白的百分比提高12倍。取食人工饲料的雌虫中,脂肪体RNA含量及其转译活性均极低,转译产物中不存在卵黄原蛋白多肽。保幼激素类似物能显著提高脂肪体RNA的含量及其中可转译mRNA的水平。处理后的雌虫,象蚜虫饲养的成熟雌虫一样,其脂肪体RNA能在体外转译系统中指导卵黄原蛋白多肽的合成,并在变性琼脂糖凝胶电泳上显示一条高分子量的带(约5100核苷酸),初步鉴定为卵黄原蛋白mRNA。由此证明,保幼激素类似物能诱导卵黄原蛋白mRNA的出现和积累。

EXPRESSION OF VITELLOGENIN GENES IN COCCINELLA SEPTEMPUNCTATA: INDUCTION OF mRNA BY JUVENILE HORMONE ANALOGUE

The expression of vitellogenin (Vg) genes in fat body of adult female Coccinella septem-punctata is regulated by juvenile hormone. When adult females were fed with a basic artificial diet, synthesis of Vg was inhibited by 97% and stimulated to 26% above the normal by administration of (RS)-hydroprene. The action of hydroprene is highly selective, causing a 12-fold increase in the proportion of Vg in total protein.In adult females feeding on artificial diet, not only the content, but also the translational activity of fat body RNA were very low. No Vg polypeptides could be detected in the translation product. Treatment with hydroprene caused 3-4 times increase in RNA content and doubled the level of translatable mRNA. Fat body RNA from hormone-treated females directed the synthesis of larger Vg polypeptides in a mRNA-dependent reticulocyte lysate system, as did the RNA from the reproductive females reared with aphids.Agrose gel electrophoresis of denatured fat body RNA from reproductive and hormone-treated females showed the presence of a high-rnolecular-weight band (5100 nucleotides), which was absent from the RNA of male and untreated female fat body. The occurrence and size of this band suggested that it was Vg mRNA.The results demonstrated that the Vg genes in the fat body of females on artificial diet are in an almost inactive state, and they are turned on in the presence of juvenile hormone, so that Vg mRNA accumulates.