Interaction and colocalization of CaBP4 and Unc119 (MRG4) in photoreceptors

¹ Department of Ophthalmology, University of Washington, 1959, NE Pacific St--Box 356485, Seattle, Washington, 98195-6485, United States

^* To whom correspondence should be addressed. E-mail: fanfan{at}u.washington.edu.

	Abstract

Purpose: To characterize the interaction of the neuron-specific protein, CaBP4, with the synaptic photoreceptor protein, Unc119 homolog (MRG4). Methods: The interaction of CaBP4 and Unc119 was studied using affinity chromatography, yeast 2-hybrid system, coimmunoprecipitation and gel overlay assay. The colocalization of CaBP4 and Unc119 was analyzed using immunohistochemistry. Unc119, CaBP4, and synaptic proteins were examined in photoreceptors using immunohistochemistry and in synaptic tangential sections of flat-mounted frozen retinas using Western blot analysis. Results: Biochemical evidence supported the interaction of CaBP4 with Unc119. CaBP4 and Unc119 colocalized in the photoreceptor synapse of adult retina and during postnatal retinal development. A reduction in Unc119 levels was observed in the photoreceptor terminals of CaBP4-knockout mice compared with wild-type mice and was higher than the reduction of other synaptic proteins. Conclusions: This study provides evidence for the interaction of CaBP4 with Unc119 at the photoreceptor synapse. This interaction suggests a functional relationship between CaBP4 and Unc119, further supporting a role for these proteins in neurotransmitter release and in the maintenance of the photoreceptor synapse.

Key Words: synaptic terminals, rods, cones, Ca2+-binding protein

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