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Sameila Okpodu, Chunqiao Liu, Helen May-Simera, Werner Graf, Anand Swaroop, Tiansen Li; Functional Investigation of the Role of Prickle 2 in Retinal Photoreceptors. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2983. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Prickle 2, a cytoplasmic protein, is a core component of the planar cell polarity (PCP) signaling pathway. PCP signaling is critical for many aspects of development in numerous organ systems. Neural Retinal Leucine Zipper (Nrl) is a transcription factor responsible for rod photoreceptor fate determination. In the absence of Nrl, rod precursors fail to develop mature rods resulting in a cone dominated retina. In Nrl knockout retina, Prickle 2 (Pk2) expression is upregulated. We posit that Pk2 may play a role in the determination, differentiation, and/or maturation of cone photoreceptors. To investigate the plausibility of this hypothesis we examined expression and function of Pk2 in the mammalian retina.
In situ hybridization was used to identify cell type specific localization of Pk2 expression in the retina.Immunoblotting,using polyclonal antibodies against Pk2,and RNA sequencing were used to study temporal expression of Pk2 during retinal development.Outer retinal function of Pk2 knockout mice was assessed by electroretinography (ERG).Quantification of retinal integrity was accomplished through spectral domain-optical coherence tomography (SD-OCT) and histological analysis of age-matched Pk2 wild-type and knockout adult mice.
In situ hybridization at postnatal day 21 confirms Pk2 expression in the Inner Nuclear Layer and the Ganglion Cell Layer of the retina. Immunoblotting using wild-type retina shows Pk2 is expressed after P10 and continues to be expressed in the adult retina; time points that do not coincide with photoreceptor development. In adult retina, RNA sequencing data shows relatively low expression levels of Pk2 in the photoreceptor cells. ERG recordings show no statistical difference between the a-wave of adult wild-type and knockout retinas, suggesting no major deficit in photoreceptor function. SD-OCT and histological analyses reflect overall retention of retinal layer integrity and cell specification, however, the central retina is thinner in the mutants.
Analysis of the effect of Pk2 in the retina suggests that this gene is likely not playing a major, non-redundant, role in photoreceptor development and/or function. While Pk2 is markedly expressed in the inner retina, lack of an overt phenotype may be explained by possible functional redundancy with Pk1. Further work is in progress that will investigate the retinal phenotype of a Pk1 and Pk2 double knockout.
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