Expression of phototransduction cascade genes in the ground squirrel retina

This study describes the expression and distribution of phototransduction cascade gene products in the cone-dominant retina of the ground squirrel Spermophilus tridecemlineatus.

Messenger RNA expression was studied by blot hybridization, and the distribution of the gene products was investigated by immunocytochemistry.

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.

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.