Gautam Naveen-Kumar, Tapadia Madhu G
Department of Zoology, Banaras Hindu University, Varanasi, India.
Int J Dev Biol. 2010;54(4):635-42. doi: 10.1387/ijdb.092910ng.
Drosophila development is a tightly regulated process involving metamorphosis of a relatively less mobile larva to a highly motile adult, triggered by secretion of 20-hydroxyecdysone. Under the influence of ecdysone, most of the larval tissues degenerate, while the imaginal cells differentiate and form adult specific structures. Although the larval Malpighian tubules do not seem to be affected by ecdysone during metamorphosis, we show that ecdysone signaling plays an important role in the early development and functioning of Malpighian tubules. Disruption of ecdysone receptor function, using targeted expression of dominant negative ecdysone receptor in stellate cells, results in disruption of organization of Malpighian tubules. The number of stellate cells is reduced in such Malpighian tubules. Further, they get clustered rather than distributed in their characteristic wild type pattern. We also demonstrate that expression of Drosophila integrin protein (DRIP), an aquaporin responsible for trans-cellular water transport, is also reduced in stellate cells when ecdysone signaling is disrupted. Our results show that of the three ecdysone receptor isoforms, only EcR-B2 rescues these phenotypes. A similar pattern of stellate cell clustering and reduced expression of DRIP is observed in ecd(1), a temperature sensitive mutant, under non-permissive conditions. These results suggest that ecdysone signaling is required for proper patterning and functioning of stellate cells and that EcR-B2 may be the primary isoform required for ecdysone signaling in stellate cells.
果蝇发育是一个受到严格调控的过程，涉及相对不太活动的幼虫变态为高度活动的成虫，这一过程由20-羟基蜕皮激素的分泌触发。在蜕皮激素的影响下，大多数幼虫组织退化，而成虫细胞分化并形成成虫特有的结构。虽然幼虫的马氏管在变态过程中似乎不受蜕皮激素的影响，但我们发现蜕皮激素信号传导在马氏管的早期发育和功能中起着重要作用。通过在星状细胞中靶向表达显性负性蜕皮激素受体来破坏蜕皮激素受体功能，会导致马氏管组织紊乱。在这样的马氏管中，星状细胞的数量减少。此外，它们会聚集在一起，而不是以其特有的野生型模式分布。我们还证明，当蜕皮激素信号传导被破坏时，负责跨细胞水运输的水通道蛋白果蝇整合素蛋白（DRIP）在星状细胞中的表达也会降低。我们的结果表明，在三种蜕皮激素受体异构体中，只有EcR-B2能挽救这些表型。在非允许条件下，在温度敏感突变体ecd(1)中观察到类似的星状细胞聚集模式和DRIP表达降低的情况。这些结果表明，蜕皮激素信号传导是星状细胞正常模式形成和功能所必需的，并且EcR-B2可能是星状细胞中蜕皮激素信号传导所需的主要异构体。
