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V.B. Mahajan, N.B. Akhmedov, S. Tsang, J. Kong, P. Gouras, D. Farber; Structural And Functional Studies Of PNR (NR2E3) . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4747.
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© ARVO (1962-2015); The Authors (2016-present)
PNR, also known as NR2E3, is a nuclear receptor that appears to be a dual regulator: it suppresses cone cell proliferation in mitotic progenitor cells, but it activates rod cell genesis in postmitotic cells. PNR has a DNA–binding domain (DBD) near the N–terminal and also a ligand–binding domain (LBD) in the C–terminal for an unknown ligand. To resolve the significance of the two distinct functional domains, we selectively removed either the DBD or LBD coding sequences from our expression cassette. A wild type PNR expression construct was used as a control.
Expression constructs for mutant PNR contain the mouse Pax6 alpha–promoter, PNR cDNA, an IRES–EGFP gene (IRES, an internal ribosome entry site from the encephalomyocarditis virus to direct the translation of the enhanced Green Fluorescence Protein, EGFP), and the polyadenylation signal. All constructs were sequenced to confirm the introduction of the specific deletions and that no other changes had been created inadvertently. Transgenic animals and age–matched littermate controls were examined for the presence of fundus autofluorescence non–invasively with a stereo fluorescence microscope that was adapted for fundus imaging, using a filter cube for green fluorescence protein. Full–field ERGs were performed with Ganzfeld stimulation. Fundus angiography was performed after intraperitoneal injection of sulforhodamine 101.
The Pax6 promoter elements initiated expression of PNR at the neuroblast stage of photoreceptor differentiation. Fundus examination of DBD mice showed increased autofluorescence and some white–yellow lesions predominantly in the optic nerve areas. The retinal vasculature was attenuated. ERGs at the maximal stimulation were extinguished bilaterally at 16 months of age. Histology revealed unusual photoreceptor patterning. Fundus examination of LBD mice showed an increased autofluorescence and some white–yellow lesions predominantly in the posterior pole. Maximal ERGs had a non–detectable a– wave but a 30 mV b–wave at 16 months of age.
Both DBD and LBD domains of PNR are essential for photoreceptors function and survival.
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