Snigirevskaya E S, Hays A R, Raikhel A S
Department of Entomology, S-136 Plant Biology Building, Michigan State University, East Lansing, Michigan 48824-1115, USA.
Cell Tissue Res. 1997 Oct;290(1):129-42. doi: 10.1007/s004410050915.
The vitellogenic female fat body of the mosquito Aedes aegypti produces three yolk protein precursors that are deposited in the yolk bodies of developing oocytes: vitellogenin, vitellogenic carboxypeptidase (VCP), and 44-kDa protein (44KP). We have used gold immunocytochemistry to investigate the pathways of their secretion in fat body trophocytes and their internalization by oocytes. In fat body trophocytes, all three yolk protein precursors are co-localized in the Golgi complex and secretory granules, indicating that they proceed simultaneously through the secretory pathway. The lysosomal system plays an important role in the termination of vitellogenesis in mosquito trophocytes, by degrading biosynthetic organelles and secretory granules. At this time, VCP and 44KP are found together with vitellogenin in trophocyte autophagolysosomes, suggesting that all three yolk protein precusors are redirected from the secretory to the lysosomal degradative pathway. Localization of VCP and 44KP in developing mosquito oocytes clearly shows that the internalization of these yolk protein precursors by oocytes occurs via the same endocytotic route as vitellogenin: all three yolk protein precursors are found on the oocyte microvillus membrane, in coated vesicles, and early endosomes. They are observed intermixed with one another in the late endosomes or in transitional yolk bodies. In mature yolk bodies, however, 44KP and VCP are segregated from vitellin, the crystallized storage form of vitellogenin; 44KP and VCP reside in the non-crystalline cortex, surrounding the vitellin core in nature yolk bodies.
埃及伊蚊的卵黄生成期雌蚊脂肪体产生三种卵黄蛋白前体，它们沉积在发育中卵母细胞的卵黄小体中：卵黄原蛋白、卵黄生成羧肽酶（VCP）和44 kDa蛋白（44KP）。我们利用金免疫细胞化学技术研究了它们在脂肪体营养细胞中的分泌途径以及被卵母细胞内化的过程。在脂肪体营养细胞中，所有三种卵黄蛋白前体都共定位于高尔基体复合体和分泌颗粒中，这表明它们同时通过分泌途径进行。溶酶体系统在蚊营养细胞的卵黄生成终止过程中发挥重要作用，通过降解生物合成细胞器和分泌颗粒来实现。此时，在营养细胞自噬溶酶体中发现VCP和44KP与卵黄原蛋白在一起，这表明所有三种卵黄蛋白前体都从分泌途径转向了溶酶体降解途径。VCP和44KP在发育中的蚊卵母细胞中的定位清楚地表明，这些卵黄蛋白前体被卵母细胞内化是通过与卵黄原蛋白相同的内吞途径进行的：所有三种卵黄蛋白前体都存在于卵母细胞微绒毛膜上、被膜小泡和早期内体中。在晚期内体或过渡性卵黄小体中可以观察到它们相互混合。然而，在成熟的卵黄小体中，44KP和VCP与卵黄磷蛋白（卵黄原蛋白的结晶储存形式）分离；在天然卵黄小体中，44KP和VCP存在于非结晶皮质中，围绕着卵黄磷蛋白核心。
