THE EMBRYONIC PINEAL-BODY AS A MULTIPOTENT ORGAN

The repertoire of differentiating potency of mammalian and avian pineal cells has been examined utilizing cell culture technique. Skeletal muscle fibers are differentiated from pineal cells of the rat under the usual culture condition and from those of quail under hypertonic conditions. Myogenesis of pineal cells may be explained from the ontogeny of the pineal body. Anlagen of a pineal body are situated in bilateral cephalic neural folds, which also supply multipotent neural crest cells. In some conditions, almost all quail pineal cells are able to differentiate into pigmented epithelial cells and/or lens cells. Opsin containing cells found in culture of rat pineal cells may be in a similar category reflecting the "third eye": the phylogenetic ancestor of the pineal body of avian and mammalian species. Neuron-like cells have also been reported and neuronal morphology has been intensified under the effect of testicular hyaluronidase. The cytodifferentiation described above is suggested to be different expressions of a single type of progenitor cells in the pineal body. In relation to multipotentiality of pineal cells, the original differentiating state of pineal cells is interesting; it has been found that tyrosinase is expressed from the beginning of pineal formation and that its expression is stage-specific (during embryonic period) and site-specific (predominance in the dorsal half of the pineal body and in the apical cytoplasm of the pineal cell). In the 8 day quail embryo used for culture studies, three differentiating states as to tyrosinase are noticed. However, the distinction may be apparent, as even the cells negative in tyrosinase in this stage are still ready to express tyrosinase in the suitable culture condition. Pineal cells are flexible and surprisingly susceptible to environmental factors and useful for the study of cell differentiation in general.