Resource: A multi-species multi-timepoint transcriptome database and webpage for the pineal gland and retina.

The website and database https://snengs.nichd.nih.gov provides RNA sequencing data from multi-species analysis of the pineal glands from zebrafish (Danio rerio), chicken (White Leghorn), rat (Rattus novegicus), mouse (Mus musculus), rhesus macaque (Macaca mulatta), and human (Homo sapiens); in most cases, retinal data are also included along with results of the analysis of a mixture of RNA from tissues. Studies cover day and night conditions; in addition, a time series over multiple hours, a developmental time series and pharmacological experiments on rats are included. The data have been uniformly re-processed using the latest methods and assemblies to allow for comparisons between experiments and to reduce processing differences. The website presents search functionality, graphical representations, Excel tables, and track hubs of all data for detailed visualization in the UCSC Genome Browser. As more data are collected from investigators and improved genomes become available in the future, the website will be updated. This database is in the public domain and elements can be reproduced by citing the URL and this report. This effort makes the results of 21st century transcriptome profiling widely available in a user-friendly format that is expected to broadly influence pineal research.

The Retinal Circadian Clock and Photoreceptor Viability.

Circadian rhythms are present in most living organisms, and these rhythms are not just a consequence of the day/night fluctuation, but rather they are generated by endogenous biological clocks with a periodicity of about 24 h. In mammals, the master pacemaker of circadian rhythms is localized in the suprachiasmatic nuclei (SCN) of the hypothalamus. The SCN controls circadian rhythms in peripheral organs. The retina also contains circadian clocks which regulate many aspects of retinal physiology, independently of the SCN. Emerging experimental evidence indicates that the retinal circadian clocks also affect ocular health, and a few studies have now demonstrated that disruption of retinal clocks may contribute to the development of retinal diseases. Our study indicates that in mice lacking the clock gene Bmal1, photoreceptor viability during aging is significantly reduced. Bmal1 knockout mice at 8-9 months of age have 20-30% less nuclei in the outer nuclear layer. No differences were observed in the other retinal layers. Our study suggests that the retinal circadian clock is an important modulator of photoreceptor health.

Regulation of arylalkylamine N-acetyltransferase (AANAT) in the retina.

Melatonin synthesis in retinal photoreceptors is under photic and circadian control and is regulated primarily by changes in the activity of arylalkylamine N-acetyltransferase (AANAT). Previous investigations demonstrated that Aanat transcripts are predominantly expressed in the photoreceptor cells. AANAT activity is high at night and low during the day, and illumination of the retina during the night induces rapid reduction in the activity of this enzyme. The enzyme is subject to both transcriptional and post-translational regulatory mechanisms. AANAT transcription is regulated directly by the circadian clock via the E-box present in the promoter region of the gene; the photic environment and circadian clock also influence AANAT transcription via cAMP-responsive elements. The stability of AANAT is regulated by cAMP, and light, which decreases cAMP levels in photoreceptor cells, results in rapid degradation of AANAT protein by proteasomal proteolysis. The circadian rhythm in the levels of Aanat mRNA in the rat retina persists after the suprachiasmatic nucleus (SCN) of the hypothalamus has been lesioned, indicative of its relative independence from the master clock in the brain. In non-mammalian vertebrates, the retinal clock controlling melatonin synthesis is in photoreceptor cells, but it has not been definitively localized in mammals. Several studies have also shown that dopamine plays an important role in the regulation of AANAT activity by acting via D2/D4-like receptors that are present on the photoreceptors. Finally, it is important to mention that AANAT, in addition to its role in melatonin synthesis, may play a detoxification role in the vertebrate retina by acetylating arylalkylamines that may react with retinaldehyde.

UV-A light regulation of arylalkylamine N-acetyltransferase activity in the chick pineal gland: role of cAMP and proteasomal proteolysis.

Acute exposure of dark-adapted, cultured chick pineal glands to UV-A light significantly decreased the tissue cAMP concentration and the activity of arylalkylamine N-acetyltransferase (AANAT), the penultimate and key regulatory enzyme in the melatonin biosynthetic pathway. The magnitude of these changes was dependent on the duration of UV-A exposure. The UV-A light-evoked decline in pineal AANAT activity was blocked by cAMP protagonists (forskolin and dibutyryl-cAMP) and by inhibitors of the proteasomal degradation pathway (MG-132, proteasome inhibitor I, and lactacystin). These results indicate that the chick pineal gland is directly sensitive to UV-A light. By analogy to white light, the suppressive action of UV-A radiation on AANAT activity in the chick pineal gland involves changes in the tissue cAMP level and enhanced proteasomal proteolysis.

K(+)-evoked depolarization induces serotonin N-acetyltransferase activity in photoreceptor-enriched retinal cell cultures. Involvement of calcium influx through l-type channels.

The roles of membrane depolarization and calcium influx in the regulation of retinal serotonin N-acetyltransferase (NAT) activity were investigated in low-density monolayer cultures of chick retinal cells, in which photoreceptors represented approximately 70% of the total cell population. NAT activity expressed by the cells in these cultures was markedly increased by elevating the concentration of extracellular K(+). Activity increased rapidly during the first 6 h of exposure to K(+), and remained elevated for at least 30 h. Chelation of calcium in the culture medium abolished the K(+)-evoked increase in NAT activity. Antagonists of voltage-sensitive calcium channels, nifedipine, methoxyverapamil (D600), Mn(2+), Mg(2+), and Cd(2+) inhibited the K(+)-evoked increase of NAT activity. Bay K 8644, a dihydropyridine calcium channel agonist, increased NAT activity when added alone and potentiated the K(+)-evoked increase of activity. The effect of Bay K 8644 was antagonized by nifedipine. Addition of nifedipine 18 h after addition of K(+), when NAT activity is elevated, caused activity to decrease to basal levels. These studies indicate that the increase of retinal NAT activity induced by K(+)-depolarization is mediated by a calcium-dependent process that involves sustained Ca(2+) influx through L-type voltage-sensitive Ca(2+)-channels.