Differentiation of pinopsin-immunoreactive cells in the developing quail pineal organ: an in-vivo and in-vitro immunohistochemical study

The avian pineal organ contains several. types of photoreceptors with diffe rent photopigments: rhodopsin, iodopsin, and pinopsin. We have previously e xamined the differentiation of both rhodopsin-like and iodopsin-like immuno reactive cells during pineal development in quail embryos to determine the onset of synthesis of specific proteins and their cellular localization. In the present study, we have performed pinopsin immunohistochemistry on in-v ivo developing and in-vitro cultured pineal organs of quail embryos. The re sults were compared with these obtained with rhodopsin and iodopsin immunoh istochemistry. In the developing pineal organs, pinopsin immunoreactivity w as detected at embryonic day 8, i.e. five days earlier than rhodopsin-like and iodopsin-like immunoreactivities. It was localized exclusively in the p rotrusions extending into the lumen throughout development, whereas rhodops in-like and iodopsin-like immunoreactivities were usually found both in cel l bodies and processes. These differences were also observed under two diff erent types of culture conditions (dissociated cell culture and organ cultu re) indicating that, in the avian pineal organ, the expression pattern of t he pinopsin gene is basically different from those of the other two pineal photopigments. The present study suggests that pineal cells have a mechanis m for the polarized transport of pinopsin molecules.