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R. E. Anderson, I. Ivanovic, A. Rajala, V. K. Gupta, R. V. Rajala; Delayed Phototransduction Recovery Kinetics in Mice With Deletion of p85 Regulatory Subunit of Phosphoinositide 3-Kinase in Rod Photoreceptor Cells. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3485.
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© ARVO (1962-2015); The Authors (2016-present)
Lipid products generated by phosphoinositide 3-kinase (PI3K), referred to as D3 phosphoinositides (PI), have been shown to mediate and regulate a variety of cellular events in specialized retinal photoreceptor cells. To investigate the biological significance of PI3K in vertebrate rod photoreceptors, we deleted the p85α regulatory subunit of PI3K gene in rod photoreceptors to examine its role in photoreceptor structure, function, and protein trafficking.
We bred mice expressing cre-recombinase in rods to mice with a floxed p85α regulatory subunit of PI3K to generate offspring with a conditional deletion of p85α in rods. Functional and structural changes were determined by ERG and morphometric analysis, respectively. We determined rhodopsin localization by immunofluorescence using anti-rod opsin antibody. The role of PI3K-generated phosphoinositides in light-dependent arrestin and transducin trafficking was determined ex vivo in retinas treated with a PI3K inhibitor.
We failed to observe any structural changes in p85α knockout mice. These mice showed no increased sensitivity to light stress-induced retinal degeneration. Rod opsin was properly localized to photoreceptor outer segments. No differences were found between wild type (WT) and knockout (KO) littermates in the amplitude of the scotopic ERG response after the initial flash. However, the twin flash ERG revealed a slight delay in recovery in KO mice compared to WT controls. In p85α KO mice the arrestin movement is not affected due to the complementation of other isoform, p85β. The light-dependent trafficking of arrestin to rod outer segments was abolished when we chemically inhibited all PI3K isoforms in dark-adapted ex vivo retinas that were subsequently brought into the light; however, transducin trafficking was not affected.
Our results provide the first evidence that rods utilize PI3K-generated phosphoinositides for photoreceptor functions. Expression of the α- and β-isoforms of p85 in rod photoreceptors suggests a redundant role in controlling PIP3 synthesis.
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