Expression of phototransduction cascade genes in the ground squirrel retina

Purpose. This study describes the expression and distribution of phototransduction cascade gene products in the cone-dominant retina of the ground squirrel Spermophilus tridecemlineatus. Methods. Messenger RNA expression was studied by blot hybridization and the distribution of the gene products was investigated by immunocytochemistry. Results. RNA blot hybridization showed messages for the α2, β1, and β3 subunits of transducin but was negative for rhodopsin, α1-transducin, and the α, β, and γ subunits of cyclic guanosine monophosphate (cGMP) phosphodiesterase. Immunocytochemical labeling indicated that the approximate ratio of the photoreceptor types in ground squirrel retina is 90.6% for green cones, 6.3% for rod-like cells, and 3.1% for blue cones. Rod-like cells were immunopositive for rhodopsin and blue opsin. All photoreceptor elements were labeled by antibodies against α1-transducin (which recognizes both the α1 and α2 isoforms). β3-transducin, and the rod γ subunit of phosphodiesterase, whereas no cells were labeled by antibodies against the rod α and β subunits of phosphodiesterase or against the rod cGMP-gated cation channel. Rod-like cells and blue cones were stained by antibodies against β1-transducin. Conclusions. The authors demonstrate new cone-like traits in the biochemical make-up of rod-like cells, and a distribution of the transducin β subunit in the ground squirrel is different from that found in other mammals.