Developmental potency of cultured pineal cells: An approach to pineal developmental biology

Abstract

The pineal organ is still an enigma in regard to its developmental and phylogenetic origin. Little is known of the mechanism involved in determination and differentiation of pineal cells and virtually no studies have been done on the induction and tissue interactions during pinealogenesis. Interest is also centered on the evolutional transformation in structure and function, which may be related to the developmental alterations in pineal morphogenesis between the lower and higher vertebrate species. For developmental studies, avian embryos have great advantages for various experimental manipulations, such as cell and organ culture, surgical operation, and in situ transfection of developmental genes. The present review describes our cell culture studies, which have been done on developing rat and quail pineal organs, in order to elucidate the developmental potency of pineal cells and the regulatory mechanism involved in the phenotypic expression of cell properties. A number of phenotypes including numerous neuron-specific substances are shown immunohistochemically to be expressed only under culture conditions, and not observed in the mature pineal organ. As development proceeds, some of the potencies for cell differentiation are lost; hence, in the mature pineal organs most neuronal phenotypes are not expressed. Numerous factors were discovered which affect phenotypic expression of cultured pineal cells in a cell-type-specific manner. These findings, together with immunohistochemical observations on developing pineal organs, reveal that the developing pineal organ is a unique and useful model system for developmental neurobiology and that cell culture techniques offer a powerful tool for the understanding of development and cell differentiation of this particular organ.

Evolution of photosensory pineal organs in new light: the fate of neuroendocrine photoreceptors

“…When cultured in the absence of norepinephrine, cells from neonatal rat pineal organs are induced to express rhodopsin immunoreactivity (Araki 1992(Araki , 2001, and respond to light by a decrease in norepinephrineinduced melatonin synthesis (Tosini et al 2000). Cultured in the presence of norepinephrine, rhodopsin expression is suppressed and the pineal cells do not become photosensory.…”

“…In the embryonic quail, there is a time-lag of 2 days between the appearance of rhodopsin-IR and iodopsin-IR pinealocytes . Moreover, in vitro studies have shown that the pineal organ of the embryonic quail contains multipotent progenitor cells that may generate different cell types under different culture conditions Araki 2001). Norepinephrine significantly suppresses differentiation of rhodopsin-IR photoreceptors, and the efficiency of this suppression decreases with age .…”

“…Norepinephrine significantly suppresses differentiation of rhodopsin-IR photoreceptors, and the efficiency of this suppression decreases with age . Growth factors differentially promote the differentiation of pineal neurons or rhodopsin-IR photoreceptors, and it appears the expression of pinopsin, rhodopsin and iodopsin is differentially regulated (Araki 2001). The sequential appearance of different opsins in the developing pineal organ could indicate that there is a progressive fate restriction with respect to photoreceptor cell types, but it does not discriminate whether different photoreceptor types are sequentially generated by common progenitors, or different committed progenitors are activated at different developmental stages.…”

Differential enhancement of neural and photoreceptor cell differentiation of cultured pineal cells by FGF‐1, IGF‐1, and EGF

“…Previous studies have shown that various cell types can be identified in embryonic pineal cultures by applying immunocytochemical methods (Araki, 2001). They can be classified into three categories: endocrinal, photoreceptive, and neuronal cells.…”

“…In lower vertebrates the pineal organ contains neurons and photoreceptors and is an important component of the photoendocrine system (Vollrath, 1981). The pineal organ and the lateral eye have several common features with respect to their develop-mental aspects (see reviews by Araki, 2001;Ekström and Meissl, 2003). Although only limited numbers of cell types differentiate in the pineal gland of higher vertebrates, embryonic pineal cells have been shown experimentally to possess a much wider spectrum of developmental potency (Okada, 1991;Araki, 2001).…”