Induction of photosensitivity in cultured rat pineal affects Aa-nat regulation

Universality and diversity in the signal transduction pathway that regulates seasonal reproduction in vertebrates

Most vertebrates living outside the tropical zone show robust physiological responses in response to seasonal changes in photoperiod, such as seasonal reproduction, molt, and migration. The highly sophisticated photoperiodic mechanism in Japanese quail has been used to uncover the mechanism of seasonal reproduction. Molecular analysis of quail mediobasal hypothalamus (MBH) revealed that local thyroid hormone activation within the MBH plays a critical role in the photoperiodic response of gonads. This activation is accomplished by two gene switches: thyroid hormone-activating (DIO2) and thyroid hormone-inactivating enzymes (DIO3). Functional genomics studies have shown that long-day induced thyroid-stimulating hormone (TSH) in the pars tuberalis (PT) of the pituitary gland regulates DIO2/3 switching. In birds, light information received directly by deep brain photoreceptors regulates PT TSH. Recent studies demonstrated that Opsin 5-positive cerebrospinal fluid (CSF)-contacting neurons are deep brain photoreceptors that regulate avian seasonal reproduction. Although the involvement of TSH and DIO2/3 in seasonal reproduction has been confirmed in various mammals, the light input pathway that regulates PT TSH in mammals differs from that of birds. In mammals, the eye is the only photoreceptor organ and light information received by the eye is transmitted to the pineal gland through the circadian pacemaker, the suprachiasmatic nucleus. Nocturnal melatonin secretion from the pineal gland indicates the length of night and regulates the PT TSH. In fish, the regulatory machinery for seasonal reproduction, from light input to neuroendocrine output, has been recently demonstrated in the coronet cells of the saccus vasculosus (SV). The SV is unique to fish and coronet cells are CSF-contacting neurons. Here, we discuss the universality and diversity of signal transduction pathways that regulate vertebrate seasonal reproduction.

Analysis of daily and circadian gene expression in the rat pineal gland

The mammalian pineal gland is an important component of the circadian system. In the present study, we examined the expression of roughly 8000 genes in the rat pineal gland as a function of time of day under light-dark (LD) cycles and in constant dark (DD) using oligo DNA microarray technique. We identified 47 and 13 genes that showed higher levels at night and day, respectively, under LD. The same patterns of expression were also observed in DD. About half of the genes that peaked at night have a known biological function, i.e., transcription factors and proteins that are involved in signaling cascades, whereas 14 are expressed sequence tags and 8 have an unknown biological function. Twelve of the genes that were up-regulated at night were also up-regulated after 1h NE stimulation, thus suggesting that the expression of these genes is controlled by adrenergic mechanisms. Of the 13 genes that were up-regulated in the daytime, 6 coded for proteins that are involved in intracellular signaling pathways. The results obtained with microarray analysis were well correlated with data obtained using real time quantitative RT-PCR. The present results provide new materials to dissect and understand the pineal physiology.

Genetic aspects of melatonin biology

For decades, the important physiological roles of the pineal hormone have inspired scientific investigations. Research efforts have generated a broad amount of information relevant to various genetic aspects of melatonin biology. Nevertheless, our understanding of the effect of genetic factors upon melatonin biosynthesis and the mechanisms of gene expression regulation by melatonin in target tissues is far from complete. The present review makes an effort to summarize and systematize the existing information on the subject, sequentially discussing (i) the effect of genetic factors upon melatonin biosynthesis, (ii) melatonin receptor expression profiles, and (iii) the effect of melatonin upon expression of genes in target tissues.

Effects of photoperiod on the development of the central glutamate system in tilapia, Oreochromis mossambicus

The effect of photoperiod (light/dark cycle) on the development of the central glutamate system was investigated in tilapia, Oreochromis mossambicus. Tilapia, at 0, 5, and 10 days posthatching were respectively divided into three equal groups to be kept in different photoperiods: 12/12 h, 24/0 h (full day), and 0/24 h (full night). Neither the full-day nor the full-night photoperiod showed any influence on the development of the central glutamate system, including glutamate content and mRNA expression of glutamate receptor 3 alpha, in the developing tilapia brain. These results suggest that neither constant light nor dark photoperiods affected the influence of the central glutamate system on brain sex differentiation in tilapia during the early developing period.