Insect Bacterial Symbiont-Mediated Vitellogenin Uptake into Oocytes To Support Egg Development.
Insect Bacterial Symbiont-Mediated Vitellogenin Uptake into Oocytes To Support Egg Development.
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作者：
Mao Q;Wu W;Huang L;Yi G;Jia D;Chen Q;Chen H;Wei T
许多昆虫体内都有专性的细菌共生体，这些共生体可以由雌性昆虫通过卵垂直传播给后代。在这里，我们报告，叶蝉卵黄蛋白原（Vg）识别和结合的表面通道分子（孔蛋白）上的专性细菌共生体Nasuia，这可能会导致开放的孔蛋白通道Vg访问细胞质的Nasuia的信封。因此，Vg可以利用细菌共生体作为独立的载体进入卵母细胞。这种携带的Vg内容物支持有效的昆虫卵发育。因此，我们的研究结果表明，昆虫已经进化出策略，利用共生体携带额外的Vgs，以保证最佳的昆虫繁殖。许多昆虫物种，如蚜虫、叶蝉、稻飞虱和粉虱，都有专性的细菌共生体，这些共生体可以通过雌性昆虫的卵母细胞经卵母细胞传播给后代。专性细菌共生体是否能够携带重要的分子/资源到胚胎以支持卵子发育仍然是未知的。在这里，我们表明，卵黄蛋白原（Vg）前体的水稻叶蝉黑尾叶蝉是生物合成的脂肪体，分泌到血淋巴，随后裂解成35和178 kDa的亚基，而只有178-kDa亚基被受体中卵母细胞的前端吸收，或以受体非依赖性方式移动到与专性细菌共生体“三角脑藻”（下文称为Nasuia）相关的终末卵母细胞的后极。此外，178-kDa的Vg亚基可以直接与Nasuia包膜上的表面通道分子（孔蛋白）相互作用，使Vg进入细菌细胞质。因此，Vg可以搭便车古老的卵母细胞进入路径的Nasuia，共同专性共生体的叶蝉。敲低Nasuia生长相关蛋白表达或用孔蛋白抗体处理强烈阻止Nasuia将Vgs携带到卵母细胞中并损害昆虫卵发育的能力。在发育中的卵中，Nasuia携带的Vg提供至少20%的总Vg。我们预计，细菌共生体介导的Vg摄取到卵母细胞，以支持有效的卵发育可能是一个共同的模式，许多昆虫共享。
Many insects harbor obligate bacterial symbionts that can be vertically transmitted to offspring by female insects through eggs. Here, we report that leafhopper vitellogenin (Vg) recognizes and binds a surface channel molecule (porin) on the envelope of obligate bacterial symbiont Nasuia, which potentially induces the opening of porin channels for Vg to access the cytoplasm of Nasuia. Thus, Vg can exploit bacterial symbionts as the independent carriers into the oocytes. Such Nasuia-carried Vg contents support efficient insect egg development. Thus, our findings indicate that insects have evolved strategies to exploit the symbionts for carrying additional Vgs to guarantee optimal insect reproduction. Many insect species, such as aphids, leafhoppers, planthoppers, and whiteflies harbor obligate bacterial symbionts that can be transovarially transmitted to offspring through the oocytes of female insects. Whether obligate bacterial symbionts can carry important molecules/resources to the embryos to support egg development is still unknown. Here, we show that the vitellogenin (Vg) precursor of rice leafhopper Nephotettix cincticeps is biosynthesized by the fat body, secreted into the hemolymph and subsequently cleaved into the 35- and 178-kDa subunits, whereas only the 178-kDa subunit is taken up by the leading end of oocytes in a receptor-dependent manner or moves into the posterior pole of the terminal oocyte in association with obligate bacterial symbiont “Candidatus Nasuia deltocephalinicola” (hereafter Nasuia) in a receptor-independent manner. Furthermore, the 178-kDa Vg subunit can directly interact with a surface channel molecule (porin) on the envelope of Nasuia, allowing Vg to enter bacterial cytoplasm. Thus, Vg can hitchhike the ancient oocyte entry path of Nasuia, the common obligate symbiont of leafhoppers. Knocking down a Nasuia growth-related protein expression or treatment with porin antibody strongly prevents the ability of Nasuia to carry Vgs into oocytes and impair insect egg development. Nasuia-carried Vgs provide at least 20% of the total Vgs in the developing eggs. We anticipate that the bacterial symbiont-mediated Vg uptake into oocytes to support efficient egg development may be a common pattern shared by many insects.