Department of Life Science, Tunghai University, R,O,C 407, Taiwan.
J Biomed Sci. 2012 Dec 10;19(1):101. doi: 10.1186/1423-0127-19-101.
The tubby (tub) and tubby-like protein (tulp) genes encode a small family of proteins found in many organisms. Previous studies have shown that TUB and TULP genes in mammalian involve in obesity, neural development, and retinal degeneration. The purpose of this study was to investigate the role of Drosophila king tubby (ktub) in rhodopsin 1 (Rh1) endocytosis and retinal degeneration upon light stimulation.
Drosophila ktub mutants were generated using imprecise excision. Wild type and mutant flies were raised in dark or constant light conditions. After a period of light stimulation, retinas were dissected, fixed and stained with anti-Rh1 antibody to reveal Rh1 endocytosis. Confocal and transmission electron microscope were used to examine the retinal degeneration. Immunocytochemical analysis shows that Ktub is expressed in the rhabdomere domain under dark conditions. When flies receive light stimulation, the Ktub translocates from the rhabdomere to the cytoplasm and the nucleus of the photoreceptor cells. Wild type photoreceptors form Rh1-immunopositive large vesicles (RLVs) shortly after light stimulation. In light-induced ktub mutants, the majority of Rh1 remains at the rhabdomere, and only a few RLVs appear in the cytoplasm of photoreceptor cells. Mutation of norpA allele causes massive Rh1 endocytosis in light stimulation. In ktub and norpA double mutants, however, Rh1 endocytosis is blocked under light stimulation. This study also shows that ktub and norpA double mutants rescue the light-induced norpA retinal degeneration. Deletion constructs further demonstrate that the Tubby domain of the Ktub protein participates in an important role in Rh1 endocytosis.
The results in this study delimit the novel function of Ktub in Rh1 endocytosis and retinal degeneration.
肥胖（tub）和肥胖样蛋白（tulp）基因编码存在于许多生物中的一小类蛋白质。先前的研究表明，哺乳动物中的 TUB 和 TULP 基因参与肥胖、神经发育和视网膜变性。本研究旨在探讨果蝇 king tubby（ktub）在光刺激下视紫红质 1（Rh1）内吞作用和视网膜变性中的作用。
利用不精确切除产生了果蝇 ktub 突变体。野生型和突变型果蝇在黑暗或持续光照条件下饲养。在一段时间的光照刺激后，取出视网膜，用抗 Rh1 抗体固定和染色，以显示 Rh1 内吞作用。共聚焦和透射电子显微镜用于检查视网膜变性。免疫细胞化学分析表明，Ktub 在黑暗条件下表达于光感受器细胞的纤毛杆域。当苍蝇受到光刺激时，Ktub 从纤毛杆转移到光感受器细胞的细胞质和核内。野生型光感受器细胞在光刺激后短时间内形成 Rh1-免疫阳性大泡（RLVs）。在光诱导的 ktub 突变体中，大部分 Rh1 仍留在纤毛杆，只有少数 RLVs 出现在光感受器细胞质中。norpA 等位基因突变导致光刺激下大量 Rh1 内吞作用。然而，在 ktub 和 norpA 双突变体中，光刺激下 Rh1 内吞作用被阻断。本研究还表明，ktub 和 norpA 双突变体挽救了光诱导的 norpA 视网膜变性。缺失构建体进一步表明，Ktub 蛋白的 Tubby 结构域参与了 Rh1 内吞作用的重要作用。
本研究结果限定了 Ktub 在 Rh1 内吞作用和视网膜变性中的新功能。
