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Sara Hayden, Susan Brockerhoff; Phosphoinositides and membrane trafficking in zebrafish cone inner segments. Invest. Ophthalmol. Vis. Sci. 2013;54(15):4082.
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© ARVO (1962-2015); The Authors (2016-present)
Protein transport to the outer segment of photoreceptors is well characterized, but much less is known about the sorting and transport of proteins to cellular compartments within the inner segment or to the synapse. Phosphoinositides occur on the cytosolic surface of membranes, bind to effector proteins and are required for proper vesicular trafficking. Further, the zebrafish nrc mutant ,which lacks the PI(4,5)P2 phosphatase Synaptojanin 1, aberrantly accumulates vesicles within the cone inner segment highlighting the importance of phosphoinositides in sorting within this part of the cell. In this study, we dissect mechanisms by which phosphoinosites regulate transport within cone inner segments.
We expressed the PI(4,5)P2 indicator PLCδ transiently in WT zebrafish cone photoreceptors. At 5 days postfertilization, cones expressing PLCδ were analyzed with confocal microscopy. PLCδ distribution was also analyzed in nrc mutant cones and after treating larvae with chemical agents to inhibit kinases and phosphatases that regulate phosphoinositide levels.
PI(4,5)P2 concentrates at the synapse of cone photoreceptors and in the plasma membrane. Little PI(4,5)P2 appears to be in the outer segment discs. In nrc mutants, PI(4,5)P2 levels at the synapse are increased compared to WT. Further, mutants have a centrally located accumulation of PI(4,5)P2 in cone inner segments. We are currently investigating PI(4,5)P2 after treatment with drugs that alter phosphoinositide levels.
Our work demonstrates that altered PI(4,5)P2 levels cause aberrant vesicle accumulation and disrupt normal PI(4,5)P2 distribution. Our long term goal is to understand why disrupting PI(4,5)P2 causes these phenotypes. Our work will provide fundamental information about the regulation of trafficking in photoreceptors. This information will help treat and cure retinal diseases due to abnormal vesicular sorting and transport.
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