Retinal differentiation from multipotential pineal cells of the embryonic quail

Pineal anlage tumour - a rare entity with divergent histology

Pineal anlage tumour is a rare tumour of the pineal gland that is not listed in the 2007 World Health Organization classification of tumours of the central nervous system. Pineal anlage has been defined as a primary pineal tumour with both neuroepithelial and ectomesenchymal differentiation but without endodermal differentiation. We report a pineal anlage tumour in a 4-month-old boy, the youngest patient reported with this rare tumour, with a brief review of the literature. Clinicians and neuropathologists should be aware of this entity as it is likely to be misdiagnosed as a teratoma or a melanocytic tumour of the central nervous system.

Evolution of The Vertebrate Pineal Gland: The Aanat Hypothesis

The defining feature of the pineal gland is the capacity to function as a melatonin factory that operates on a approximately 24 h schedule, reflecting the unique synthetic capacities of the pinealocyte. Melatonin synthesis is typically elevated at night and serves to provide the organism with a signal of nighttime. Melatonin levels can be viewed as hands of the clock. Issues relating to the evolutionary events leading up to the immergence of this system have not received significant attention. When did melatonin synthesis appear in the evolutionary line leading to vertebrates? When did a distinct pineal gland first appear? What were the forces driving this evolutionary trend? As more knowledge has grown about the pinealocyte and the relationship it has to retinal photoreceptors, it has become possible to generate a plausible hypothesis to explain how the pineal gland and the melatonin rhythm evolved. At the heart of the hypothesis is the melatonin rhythm enzyme arylalkylamine N-acetyltransferase (AANAT). The advances supporting the hypothesis will be reviewed here and expanded beyond the original foundation; the hypothesis and its implications will be addressed.

NeuroD1: developmental expression and regulated genes in the rodent pineal gland

NeuroD1/BETA2, a member of the bHLH transcription factor family, is known to influence the fate of specific neuronal, endocrine and retinal cells. We report here that NeuroD1 mRNA is highly abundant in the developing and adult rat pineal gland. Pineal expression begins in the 17-day embryo at which time it is also detectable in other brain regions. Expression in the pineal gland increases during the embryonic period and is maintained thereafter at levels equivalent to those found in the cerebellum and retina. In contrast, NeuroD1 mRNA decreases markedly in non-cerebellar brain regions during development. Pineal NeuroD1 levels are similar during the day and night, and do not appear to be influenced by sympathetic neural input. Gene expression analysis of the pineal glands from neonatal NeuroD1 knockout mice identifies 127 transcripts that are down-regulated (>twofold, p < 0.05) and 16 that are up-regulated (>twofold, p < 0.05). According to quantitative RT-PCR, the most dramatically down-regulated gene is kinesin family member 5C ( approximately 100-fold) and the most dramatically up-regulated gene is glutamic acid decarboxylase 1 ( approximately fourfold). Other impacted transcripts encode proteins involved in differentiation, development, signal transduction and trafficking. These findings represent the first step toward elucidating the role of NeuroD1 in the rodent pinealocyte.

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

There are several common features between the pineal organ and the lateral eye in their developmental and evolutionary aspects. The avian pineal is a photoendocrine organ that originates from the diencephalon roof and represents a transitional type between the photosensory organ of lower vertebrates and the endocrine gland of mammals. Previous cell culture studies have shown that embryonic avian pineal cells retain a wide spectrum of differentiative capacities, although little is known about the mechanisms involved in their fate determination. In the present study, we investigated the effects of various cell growth factors on the differentiation of photoreceptor and neural cell types using pineal cell cultures from quail embryos. The results show that IGF-1 promotes differentiation of rhodopsin-immunoreactive cells, but had no effect on neural cell differentiation. Simultaneous administration of EGF and IGF-1 further enhanced differentiation of rhodopsin-immunoreactive cells, although the mechanism of the synergistic effect is unknown. FGF-1 did not stimulate proliferation of neural progenitor cells, but intensively promoted and maintained expression of a neural cell phenotype. FGF-1 appeared to lead to the conversion from an epithelial (endocrinal) to a neuronal type. It also enhanced phenotypic expression of retinal ganglion cell markers but rather suppressed expression of an amacrine cell marker. These results indicate that growth factors are important regulatory cues for pineal cell differentiation and suggest that they play roles in determining the fate of the pineal organ and the eye. It can be speculated that the differences in environmental cues between the retina and pineal may result in the transition of the pineal primordium from a potentially ocular (retinal) organ to a photoendocrine organ.

A 10-month-old boy with a large pineal tumor

February 2005. Case report of a 10-month-old boy with a large tumor located in the pineal gland, consisting of glia, ganglion cells, pigmented neuroepithelium and striated muscle, without immature components. The combination of neuroectodermal and mesenchymal constituents includes entities as pineal anlage tumor (melanotic neuroectodermal tumor of infancy, MNTI), ectomesenchymoma, medullomyoblastoma, and teratoma in the differential diagnosis. Lack of immature elements in this case, however, eliminates ectomesenchymoma and medullomyoblastoma from the differential diagnosis. Retinal anlage tumors, to be considered as MNTI at the site of the pineal gland, usually harbor immature components as well. Therefore, the present case does not match strict criteria of any of the categories mentioned and therefore we have designated it as a "pineal anlage tumor (without immature components)".

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

Pineal evolution is envisaged as a gradual transformation of pinealocytes (a gradual regression of pinealocyte sensory capacity within a particular cell line), the so-called sensory cell line of the pineal organ. In most non-mammals the pineal organ is a directly photosensory organ, while the pineal organ of mammals (epiphysis cerebri) is a non-sensory neuroendocrine organ under photoperiod control. The phylogenetic transformation of the pineal organ is reflected in the morphology and physiology of the main parenchymal cell type, the pinealocyte. In anamniotes, pinealocytes with retinal cone photoreceptor-like characteristics predominate, whereas in sauropsids so-called rudimentary photoreceptors predominate. These have well-developed secretory characteristics, and have been interpreted as intermediaries between the anamniote pineal photoreceptors and the mammalian non-sensory pinealocytes. We have re-examined the original studies on which the gradual transformation hypothesis of pineal evolution is based, and found that the evidence for this model of pineal evolution is ambiguous. In the light of recent advances in the understanding of neural development mechanisms, we propose a new hypothesis of pineal evolution, in which the old notion 'gradual regression within the sensory cell line' should be replaced with 'changes in fate restriction within the neural lineage of the pineal field'.

Effects of gonadal steroids on pineal morphogenesis and cell differentiation of the embryonic quail studied under cell culture conditions

Receptors for gonadal steroid hormones have been localized in the pineal glands of several vertebrate species. No studies, however, have reported on pineal morphogenesis and cell differentiation following hormonal application in vitro during avian embryonic development. Hormonal regulation of embryonic development is crucial in all vertebrate classes. Although gonadal hormones are known to affect organogenesis in avian embryos and chicks, we wanted to investigate whether gonadal steroids (testosterone and estradiol) have any effect on the morphogenesis and cell differentiation of the avian pineal gland. The steroid hormones had a stimulatory influence on pineal morphogenesis in vitro as evidenced from the radial arrangement of colony-forming cells and the subsequent formation of a follicular-like structure under dispersed-cell culture condition. Administration of testosterone in culture medium significantly promoted the numbers of cells that were positively stained for arginine vasopressin and tyrosine hydroxylase, while estradiol showed only a slight effect. Both of the two steroid hormones significantly decreased the numbers of cells positively stained for serotonin and melatonin. Melatonin released in the culture medium decreased in content within the 24 h following steroid treatment (supported by low immunoreactivity in cultured cells and low level released to the medium). These results clearly suggest active roles of gonadal steroid hormones on embryonic pineal morphogenesis and cell differentiation and its physiological activity as they do in adult animals.

The cellular and molecular bases of vertebrate lens regeneration

Lens regeneration takes place in some vertebrates through processes of cellular dedifferentiation and transdifferentiation, processes by which certain differentiated cell types can give rise to others. This review describes the principal forms of lens regeneration that occur in vivo as well as related in vitro systems of transdifferentiation. Classic experimental studies are reviewed that define the tissue interactions that trigger these events in vivo. Recent molecular analyses have begun to identify the genes associated with these processes. These latter studies generally reveal tremendous similarities between embryonic lens development and lens regeneration. Different models are proposed to describe basic molecular pathways that define the processes of lens regeneration and transdifferentiation. Finally, studies are discussed suggesting that fibroblast growth factors play key roles in supporting the process of lens regeneration. Retinoids, such as retinoic acid, may also play important roles in this process.

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

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.

Diffusible factors produced by cultured neural retinal cells enhance in vitro differentiation of pineal cone photoreceptors of developing quail embryos

The avian pineal is a photoreceptive organ and is believed to function as a circadian clock. Avian pineal cells are secretory rudimentary photoreceptors, and previous studies have demonstrated that there are two types of photoreceptors in developing quail pineals, one of which is rhodopsin-like immunoreactive and the other iodopsin-like immunoreactive. Much larger number of rhodopsin-like immunoreactive cells than of iodopsin-like immunoreactive cells were found in quail pineals, both in vivo and in vitro. In the present study we co-cultured pineal cells of embryonic quails with retinal cells but separated the two with a bio-membrane filter. We found that diffusible material produced by the cultured retinal cells intensely promotes the appearance of pineal iodopsin-like immunoreactive cells in vitro. This effect of retina-derived factor(s) is cell-type specific, since there is no effect on the differentiation of pineal rhodopsin-like immunoreactive cells. Retinal cell cultures had much more intensive iodopsin-promoting effect than other embryonic brain cultures such as cerebral cell cultures. The production of the retinal factor(s) seems to be developmentally regulated, since retinal cells from older embryos (E13 and older) did not have such effects. The factor(s) possibly act on pineal precursor cells by stimulating the expression of the iodopsin-like immunoreactive phenotype. Preliminary characterization of conditioned medium obtained from cultured retinal cells shows that the factor is a stable polypeptide, probably of low molecular weight. The pineal-retina culture system will provide a good experimental system to analyze the effect of extrinsic environments on cell differentiation.

Paired pineals in the developing quail (Coturnix coturnix japonica) embryos

Paired pineals were observed as an anomaly in embryonic quail brains between 7 and 9 days of incubation. The size of each pineal was almost the same as that of the normal pineal and it was located slightly lateral of the midline. Histological examination of these paired pineals revealed that both had similar cytological features in comparison with the normal pineal of the same developmental stage. No abnormal features were detected in brains and eyes of the embryos with paired pineals. Since the presumptive pineal rudiments are considered to exist in the neural folds and to fuse in the midline during the formation of the neural tube, the paired pineals may be interpreted as a result of incomplete fusion of the pineal anlagen. This report describes for the first time the symmetrical occurrence of pineal glands in the developing avian brain.

Developing rat pineal cells manifest potential of neuronal differentiation in vitro

The pineal gland in mammals is an endocrine organ and generally does not exhibit neuronal characteristics. However, it is known that under culture conditions, cells from newborn rat pineals express properties characteristic of photoreceptors. Here, we studied the potential of rat pineal cells to differentiate into neuronal cell types using different neural markers. Three phenotype markers characteristic of nerve cells, i.e., intense GABA, neuron-specific antigen (HPC-1) and microtubule-associated protein 2 (MAP2) immunoreactivities, were detected in the pineal culture of newborn rats. Expression of the respective neuronal phenotypes appears to be controlled by different mechanisms; in the normal culture medium containing 5.4 mM KCl, numerous cells were stained intensely with anti-GABA antiserum, whereas only a few were stained intensely either with HPC-1 or MAP2 antibody. In a culture medium with a high concentration of KCl (35 mM), which may induce depolarization of nerve cells, numerous cells became strongly positive for HPC-1 or MAP2; both the cell bodies and the neuritic fibers were stained positively. Since cells intensely immunoreactive to GABA, HPC-1 or MAP2 were not found in intact pineals of the rat, the present results indicate that the neuronal potency of the rat pineal cells is expressed only in vitro and is suppressed in vivo, and that the potency is lost during postnatal development. Norepinephrine at 1 microM, which suppresses differentiation of rhodopsin immunoreactive cells, was ineffective in inducing phenotypic expression of neuronal properties in the present system, indicating that the mechanism of suppression of neuronal properties in the intact pineal may be different from the one for photoreceptors.