Abstract
BackgroundThe 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.ResultsDrosophila 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.ConclusionsThe results in this study delimit the novel function of Ktub in Rh1 endocytosis and retinal degeneration.
Highlights
The tubby and tubby-like protein genes encode a small family of proteins found in many organisms
In light-induced ktub mutants, the majority of rhodopsin 1 (Rh1) remains at the rhabdomere, and only a few Rh1-immunopositive large vesicles (RLVs) appear in the cytoplasm of photoreceptor cells
The results in this study delimit the novel function of Ktub in Rh1 endocytosis and retinal degeneration
Summary
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. The role of Tulp as phagocytosis ligand occurs through binding to the MerTK, a TAM receptor tyrosine kinase subfamily [26] Together, these studies have shown important functions of Tulps in multicellular organisms. This eventually leads to the depolarization of the photoreceptor cell and neurotransmitter release. Studies in Drosophila have demonstrated that visual arrestin (Arr1) is essential for lightinduced Rh1 internalization [37] and Arr is involved in rhodopsin endocytosis under certain pathological situations [38,39,40]
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