Insects are highly successful, in part through an excellent ability to osmoregulate. The renal (Malpighian) tubules can secrete fluid faster on a per-cell basis than any other epithelium, but the route for these remarkable water fluxes has not been established. In Drosophila melanogaster, we show that 4 genes of the major intrinsic protein family are expressed at a very high level in the fly renal tissue: the aquaporins (AQPs) Drip and Prip and the aquaglyceroporins Eglp2 and Eglp4 As predicted from their structure, and by their transport function by expressing these proteins in Xenopus oocytes, Drip, Prip, and Eglp2 show significant and specific water permeability, whereas Eglp2 and Eglp4 show very high permeability to glycerol and urea. Knockdowns of any of these genes result in impaired hormone-induced fluid secretion. The Drosophila tubule has 2 main secretory cell types: active cation-transporting principal cells, wherein the aquaglyceroporins localize to opposite plasma membranes, and small stellate cells, the site of the chloride shunt conductance, with these AQPs localizing to opposite plasma membranes. This suggests a model in which osmotically obliged water flows through the stellate cells. Consistent with this model, fluorescently labeled dextran, an in vivo marker of membrane water permeability, is trapped in the basal infoldings of the stellate cells after kinin diuretic peptide stimulation, confirming that these cells provide the major route for transepithelial water flux. The spatial segregation of these components of epithelial water transport may help to explain the unique success of the higher insects in regulating their internal environments.

中文翻译：

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专门的星状细胞为果蝇肾小管的快速通水提供了一条特权途径。

昆虫非常成功，部分原因是其具有渗透压的出色能力。肾小管能够在每个细胞上比其他任何上皮细胞更快地分泌液体，但是尚未建立获得这些显着水通量的途径。在果蝇中，我们显示了主要内在蛋白家族的4个基因在蝇肾组织中以很高的水平表达：水通道蛋白（AQPs）滴灌和Prip以及水通道糖蛋白Eglp2和Eglp4从其结构预测，并通过它们在非洲爪蟾卵母细胞中表达这些蛋白的转运功能，滴灌，滴灌和Eglp2显示出明显的和特定的水渗透性，而Eglp2和Eglp4显示出对甘油和尿素的非常高的渗透性。这些基因的任何一个基因的敲除都会导致激素诱导的液体分泌受损。果蝇小管具有两种主要的分泌细胞类型：活性阳离子运输性主细胞，其中水甘油糖蛋白定位于相对的质膜；小的星状细胞，即氯分流电导的位点，这些AQP定位于相对的质膜。这暗示了渗透渗透的水流过星状细胞的模型。与该模型一致，激肽利尿肽刺激后，荧光标记的葡聚糖（一种膜透水的体内标志物）被困在星状细胞的基础折叠中，证实了这些细胞提供了上皮水通量的主要途径。这些上皮水运输成分的空间隔离可能有助于解释高等昆虫在调节其内部环境方面的独特成功。