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P Ekstrom, L Johnson, T van Veen; Akt Kinase is Present and Activated in Photoreceptors and Other Cells of the Developing Retina . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2685.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To understand the degeneration of photoreceptors in animal models of retinitis pigmentosa, e.g. the rd mouse, it is necessary to unravel the signalling pathways that govern the development and survival of these cells in normal mice. The role of the PI3-kinase/Akt-kinase (a.k.a. PKB) pathway in cell survival and differentiation is rapidly gaining attention. However, knowledge of this pathway in the retina is scant. Here we have studied the expression and activation of Akt in the developing retina, using antibodies specific for phosphorylated, i.e. activated, forms of Akt-kinase. Methods: Retinas were collected from C3H mice at various time points after birth (PN1- PN28), fixed, cryo-sectioned and immunofluorescence stained using primary, polyclonal antibodies towards the Akt per se or either of its Thr308 or Ser473 phosphorylated forms. Results: Akt was present in several cell types of the developing retina, including photoreceptors. The Thr308 phosphovariant was restricted to retinal ganglion cell fibers (neurofilament positive) in the ganglion cell layer and in the optic nerve and possibly to the ganglion cells themselves. Ser473 phospho-Akt was revealed in cell nuclei (bisbenzimide positive) in the ganglion cell layer, the inner nuclear layer and in a subpopulation of photoreceptors. In the latter, the staining changed over time, in that immunoreactivity was absent at PN5, present in cell nuclei scattered over the whole photoreceptor layer at PN11-PN14, but observed preferentially in the outermost rows of photoreceptor cell bodies at PN21. Conclusion: Akt is present in the developing mouse retina, photoreceptors included. The Thr308 and Ser473 phospho-Akt forms could also be detected, which shows that upstream Akt-activating steps were engaged in certain cells. However, the two phosphovariants had differential rather than overlapping distributions, indicating that different functions can be tied to the two phosphorylation sites. The photoreceptor nuclear staining for Ser473 phospho-Akt suggests its involvement in transcription factor control and hence differentiation phenomena of these cells.
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