Co-localization of UNC119 and Transducin α Subunit in Light-Adapted Rods

Abstract

Purpose: : UNC119 is a recently discovered protein partner of transducin α subunit (Gα_t) that participates in the light-driven transducin translocation in rods, due to its highly specific interaction with the myristoylated N-terminus of Gα_t leading to dissociation and translocation of transducin from the membrane. Here we compared the subcellular localization of UNC119 and Gα_t under different conditions of illumination.

Methods: : Pigmented mice and rats were subjected to different levels of illumination and subcellular distribution of UNC119 in rods was analyzed using immunofluorescence and Western blotting of serial tangential sections of the retina. The levels of UNC119 protein were compared in Gα_t -knockout and wild-type mice.

Results: : We found that UNC119 resides predominantly in the rod inner segment. From here some of UNC119 appeared to infiltrate the outer segment, although the apical region of this compartment contained no detectable UNC119. In addition, UNC119 was present in the cell body and synaptic region of rods, however in much smaller amounts. The profile of UNC119 subcellular distribution remains largely unchanged under all tested conditions of illumination, and it closely resembles that of Gα_t in light-adapted rods. Furthermore, in the absence of Gα_t expression, the cellular levels of UNC119 were also significantly reduced.

Conclusions: : Compartmentalization of UNC119 in the rod inner segment and at the base of the outer segment supports the notion that it is involved in the trafficking of transducin from the outer to the inner segment of rods. Downregulation of UNC119 in Gα_t-knockout mice is consistent with the role of Gα_t as a major binding partner for UNC119.

Keywords: photoreceptors • protein structure/function • signal transduction