EXPRESSION OF PHOTOTRANSDUCTION CASCADE GENES IN THE GROUND-SQUIRREL RETINA

Purpose. This study describes the expression and distribution of photo transduction 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. RN A blot hybridization showed messages for the (alpha 2, beta 1 and beta 3 subunits of transducin but was negative for rhodopsin, alpha 1-tran sducin, and the alpha, beta, and gamma subunits of cyclic guanosine mo nophosphate (cGMP) phosphodiesterase. Immunocytochemical labeling indi cated 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 recognizes both the alpha 1and alpha 2 isoforms), beta-trans ducin, and the rod gamma subunit of phosphodiesterase, whereas no cell s were labeled by antibodies against the red alpha and beta subunits o f phosphodiesterase or against the rod cGMP-gated cation channel. Rod- like cells and blue cones were stained by antibodies against beta 1-tr ansducin. 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.