The purpose of this study was to determine if the absence of guanylate cyclase-1 (RetGC1, GC1), a key visual phototransduction cascade enzyme that is expressed in both retinal photoreceptors and pinealocytes, disrupts light regulation of pinopsin mRNA levels in the chicken pineal gland. In this series of experiments, we compared levels of pinopsin and tryptophan 5-hydroxylase mRNA in the pineal glands of GUCY1B (B) and normal chickens housed under either cyclic light or constant dark conditions. The B chicken carries a null mutation in the gene encoding guanylate cyclase-1 that results in blindness in these animals at hatching. The results of our experiments show (1) that the amount of pinopsin mRNA in B pineal is significantly higher than the amount in normal pineal in both light and dark conditions, (2) that light induces an increase in pinopsin mRNA levels in B pineal, (3) that the relative magnitude of the light-induced increase in pinopsin mRNA in B pineal is not significantly different from that observed in normal pineal, and (4) that the changes in the regulation of pinopsin mRNA levels in B pineal gland are not accompanied by changes in the circadian expression of tryptophan 5-hydroxylase mRNA. These results show that the absence of guanylate cyclase-1 expression in the B pineal gland leads to a significant increase in basal levels of pinopsin mRNA in this gland but does not alter the magnitude of the increase in pinopsin mRNA levels that is observed as a result of light stimulation.
