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 alpha 2, beta 1, and beta 3 subunits of transducin but was negative for rhodopsin, alpha 1-transducin, and the alpha, beta, and gamma 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 alpha 1-transducin (which recognizes both the alpha 1 and alpha 2 isoforms), beta 3-transducin, and the rod gamma subunit of phosphodiesterase, whereas no cells were labeled by antibodies against the rod alpha and beta subunits of phosphodiesterase or against the rod cGMP-gated cation channel. Rod-like cells and blue cones were stained by antibodies against beta 1-transducin.
Conclusions: The authors demonstrate new cone-like traits in the biochemical make-up of rod-like cells, and a distribution of the transducin beta subunit in the ground squirrel is different from that found in other mammals.