Song S U, Kurkulos M, Boeke J D, Corces V G
Department of Biology, The Johns Hopkins University, Baltimore, MD 21218, USA.
Development. 1997 Jul;124(14):2789-98. doi: 10.1242/dev.124.14.2789.
The gypsy retroelement of Drosophila moves at high frequency in the germ line of the progeny of females carrying a mutation in the flamenco (flam) gene. This high rate of de novo insertion correlates with elevated accumulation of full-length gypsy RNA in the ovaries of these females, as well as the presence of an env-specific RNA. We have prepared monoclonal antibodies against the gypsy Pol and Env products and found that these proteins are expressed in the ovaries of flam females and processed in the manner characteristic of vertebrate retroviruses. The Pol proteins are expressed in both follicle and nurse cells, but they do not accumulate at detectable levels in the oocyte. The Env proteins are expressed exclusively in the follicle cells starting at stage 9 of oogenesis, where they accumulate in the secretory apparatus of the endoplasmic reticulum. They then migrate to the inner side of the cytoplasmic membrane where they assemble into viral particles. These particles can be observed in the perivitelline space starting at stage 10 by immunoelectron microscopy using anti-Env antibodies. We propose a model to explain flamenco-mediated induction of gypsy mobilization that involves the synthesis of gypsy viral particles in the follicle cells, from where they leave and infect the oocyte, thus explaining gypsy insertion into the germ line of the subsequent generation.
果蝇的吉普赛逆转座子在携带弗拉门戈（flam）基因突变的雌性后代的生殖系中高频移动。这种高频率的从头插入与这些雌性卵巢中全长吉普赛RNA的积累增加以及env特异性RNA的存在相关。我们制备了针对吉普赛Pol和Env产物的单克隆抗体，发现这些蛋白质在flam雌性的卵巢中表达，并以脊椎动物逆转录病毒特有的方式进行加工。Pol蛋白在卵泡细胞和滋养细胞中均有表达，但在卵母细胞中未积累到可检测水平。Env蛋白仅在卵子发生的第9阶段开始在卵泡细胞中表达，在那里它们在内质网的分泌装置中积累。然后它们迁移到细胞质膜的内侧，在那里组装成病毒颗粒。使用抗Env抗体通过免疫电子显微镜观察，从第10阶段开始在卵周隙中可以观察到这些颗粒。我们提出了一个模型来解释弗拉门戈介导的吉普赛动员诱导，该模型涉及在卵泡细胞中合成吉普赛病毒颗粒，它们从那里离开并感染卵母细胞，从而解释了吉普赛插入到后代的生殖系中。
