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F. I. Zuniga, J. S. Raskin, J. L. Linares, A. Swaroop, C. M. Craft; Identification and Characterization of Rnd2 as a Potential Functional Partner of Cone Arrestin. Invest. Ophthalmol. Vis. Sci. 2007;48(13):601.
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Although visual arrestins down-regulate light-activated, phosphorylated G-protein-coupled receptors and are translocated to rod and cone outer segments in a light dependent manner, their additional functions have not been elucidated. We hypothesize that visual arrestins (Arrestin1 [ARR1] and Cone arrestin [CAR]) or their alternative splice variants modulate cone pigment recovery in phototransduction and interact with other functional partners to regulate cone synaptic transmission.
A yeast two-hybrid (Y2H) cDNA library was constructed using total RNA from pure cone retinas of Nrl-knockoutmice and screened with a CAR bait to identify novel protein interactions. DNA sequencing and BLAST searches determined the identity of putative clones. In vitro binding assays, pull-down assays, RT-PCR, and immunohistochemistry were used to validate the CAR-interacting clones identified by Y2H.
The Y2H screening of 1.8 X 106 clonesidentified 500 potential cDNAs; of these, 24 were confirmed by co-transformations and further testing. Six clones, identified as Rnd2, belong to the Rho family of small GTPases, known to regulate the actin cytoskeleton in response to extracellular stimulus. Additionally, recent studies on Rnd2 propose that one of its in vivo functions is to regulate morphological and migrational changes associated with pyramidal neuronal development. Rnd2’s role in the retina and its binding characteristics with CAR are the subject of our current investigation.
Given that CAR is highly expressed throughout the cone photoreceptor and remains localized in the photoreceptor synapse even after light exposure, we propose that CAR has other cellular functions and functional partners similar to the nonvisual arrestins in cellular signaling pathways. We identified Rnd2 as a novel CAR-interacting protein that may contribute to the structure and function of the cone photoreceptor. Future studies are designed to test Rnd2 in developmental knock down experiments in zebrafish and to verify the physiological significance of the CAR-Rnd2 Y2H interactions.
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