Ret-PCP2 colocalizes with protein kinase C in a subset of primate ON cone bipolar cells.

Purkinje cell protein 2 (PCP2), a member of the family of guanine dissociation inhibitors and a strong interactor with the G-protein subunit G alpha(o), localizes to retinal ON bipolar cells. The retina-specific splice variant of PCP2, Ret-PCP2, accelerates the light response of rod bipolar cells by modulating the mGluR6 transduction cascade. All ON cone bipolar cells express mGluR6 and G alpha(o), but only a subset expresses Ret-PCP2. Here we test the hypothesis that Ret-PCP2 contributes to shaping the various temporal bandwidths of ON cone bipolar cells in monkey retina. We found that the retinal splice variants in monkey and mouse are similar and longer than the cerebellar variants. Ret-PCP2 is strongly expressed by diffuse cone bipolar type 4 cells (DB4; marked with anti-PKCalpha) and weakly expressed by midget bipolar dendrites (labeled by antibodies against G alpha(o), G gamma 13, or mGluR6). Ret-PCP2 is absent from diffuse cone bipolar type 6 (DB6; marked with anti-CD15) and blue cone bipolar cells (marked with anti-CCK precursor). Thus, cone bipolar cells that terminate in stratum 3 of the inner plexiform layer (DB4) express more Ret-PCP2 than those that terminate in strata 3 + 4 (midget bipolar cells), and these in turn express more than those that terminate in stratum 5 (DB6 and blue cone bipolar cells). This expression pattern approximates the arborization of ganglion cells (GC) with different temporal bandwidths: parasol GCs stratifying near stratum 3 are faster than midget GCs stratifying in strata 3 + 4, and these are probably faster than the sluggish GCs that arborize in stratum 5.