Interaction and colocalization of CaBP4 and Unc119 (MRG4) in photoreceptors.
OBJECTIVE
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 two-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 flatmounted 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.
Haeseleer
Françoise
F
Department of Ophthalmology, University of Washington, Seattle, Washington 98195, USA. fanfan@u.washington.edu
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D015153:Blotting, Western; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002846:Chromatography, Affinity; D003001:Cloning, Molecular; D004591:Electrophoresis, Polyacrylamide Gel; D019084:Fluorescent Antibody Technique, Indirect; D047468:Immunoprecipitation; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D013058:Mass Spectrometry; D051379:Mice; D018345:Mice, Knockout; D018613:Microscopy, Confocal; D008868:Microtubule Proteins / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D020419:Photoreceptor Cells, Vertebrate / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D011485:Protein Binding; D013569:Synapses / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
D048868:Adaptor Proteins, Signal Transducing; C494133:Cabp4 protein, mouse; D002135:Calcium-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008868:Microtubule Proteins; D009419:Nerve Tissue Proteins; C489115:Unc119 protein, mouse