Differential expression of mRNA and protein encoding retinal and pineal S-antigen during the light/dark cycle

Disrupted circadian expression of beta-arrestin 2 affects reward-related µ-opioid receptor function in alcohol dependence

There is increasing evidence for a daily rhythm of μ-opioid receptor (MOR) efficacy and the development of alcohol dependence. Previous studies show that beta-Arrestin 2 (bArr2) has an impact on alcohol intake, at least partially mediated via modulation of MOR signaling, which in turn mediates the alcohol rewarding effects. Considering the interplay of circadian rhythms on MOR and alcohol dependence, we aimed to investigate bArr2 in alcohol dependence at different time-points of the day/light cycle on the level of bArr2 mRNA (in situ hybridization), MOR availability (receptor autoradiography) and MOR signaling (Damgo-stimulated G-protein coupling) in the nucleus accumbens of alcohol-dependent and non-dependent Wistar rats. Using a microarray data set we found that bArr2, but not bArr1, shows a diurnal transcription pattern in the accumbens of naïve rats with higher expression levels during the active cycle. In three-week abstinent rats, bArr2 is upregulated in the accumbens at the beginning of the active cycle (ZT15), whereas no differences were found at the beginning of the inactive cycle (ZT3), compared to controls. This effect was accompanied with a specific downregulation of MOR binding in the active cycle. Additionally, we detect a higher receptor coupling during the inactive cycle compared to the active cycle in alcohol-dependent animals. Together, we report a daily rhythmicity for bArr2 expression linked to an inverse pattern of MOR, suggesting an involvement for bArr2 on circadian regulation of G-protein coupled receptors in alcohol dependence. The presented data may have implications for the development of novel bArr2-related treatment targets for alcoholism.

Rhythmic Regulation of Photoreceptor and RPE Genes Important for Vision and Genetically Associated With Severe Retinal Diseases

Purpose

The aim of the present study was to identify candidate genes for mediating daily adjustment of vision.

Methods

Genes important for vision and genetically associated with severe retinal diseases were tested for 24-hour rhythms in transcript levels in neuronal retina, microdissected photoreceptors, photoreceptor-related pinealocytes, and retinal pigment epithelium-choroid (RPE-choroid) complex by using quantitative PCR.

Results

Photoreceptors of wildtype mice display circadian clock-dependent regulation of visual arrestins (Arr1, Arr4) and the visual cycle gene Rdh12, whereas cells of the RPE-choroid exhibit light-dependent regulation of the visual cycle key genes Lrat, Rpe65, and Rdh5. Clock-driven rhythmicity of Arr1, Arr4, and Rdh12 was observed also in rat pinealocytes, to persist in a mouse model of diabetic retinopathy (db/db) and, in the case of Arr1, to be abolished in retinae of mice deficient for dopamine D₄ receptors. Therefore, the expression rhythms appear to be evolutionary conserved, to be unaffected in diabetic retinopathy, and, for Arr1, to require dopamine signaling via dopamine D4 receptors.

Conclusions

The data of the present study suggest that daily adjustment of retinal function combines clock-dependent regulation of genes responsible for phototransduction termination (Arr1, Arr4) and detoxification (Rdh12) in photoreceptors with light-dependent regulation of genes responsible for retinoid recycling (Lrat, Rpe65, and Rdh5) in RPE. Furthermore, they indicate circadian and light-dependent regulation of genes genetically associated with severe retinal diseases.

The expression of three opsin genes and phototactic behavior of Spodoptera exigua (Lepidoptera: Noctuidae): Evidence for visual function of opsin in phototaxis

Phototaxis in nocturnal moths is widely utilized to control pest populations in practical production. However, as an elusive behavior, phototactic behavior is still not well understood. Determination of whether the opsin gene plays a key role in phototaxis is an interesting topic. This study was conducted to analyze expression levels and biological importance of three opsin genes (Se-uv, Se-bl, and Se-lw) and phototactic behavior of Spodoptera exigua. The three opsin genes exhibited higher expression levels during daytime, excluding Se-bl in females, whose expression tended to increase at night. And cycling of opsin gene levels tended to be upregulated at night, although the magnitude of increase in females was lower than that in males exposed to constant darkness. The results of western blotting were consistent with those of qRT-PCR. Furthermore, opsin gene expression was not influenced by light exposure during the scotophase, excluding Se-uv in males, and tended to be downregulated by starvation in females and copulation in both female and male moths. To determine the relationship between opsin gene expression and phototactic behavior, Se-lw was knocked down by RNA interference. Moths with one opsin gene knocked down showed enhanced expression of the other two opsin genes, which may play important roles in compensation in vision. The Se-lw-knockdown moths exhibited reduced phototactic efficiency to green light, suggesting that Se-LW contributes to phototaxis, and increases phototactic efficiency to green light. Our finding provides a sound theoretical basis for further investigation of visual expression pattern and phototactic mechanisms in nocturnal moths.

Arrestin 1 and Cone Arrestin 4 Have Unique Roles in Visual Function in an All-Cone Mouse Retina

PURPOSE

Previous studies discovered cone phototransduction shutoff occurs normally for Arr1-/- and Arr4-/-; however, it is defective when both visual arrestins are simultaneously not expressed (Arr1-/-Arr4-/-). We investigated the roles of visual arrestins in an all-cone retina (Nrl-/-) since each arrestin has differential effects on visual function, including ARR1 for normal light adaptation, and ARR4 for normal contrast sensitivity and visual acuity.

METHODS

We examined Nrl-/-, Nrl-/-Arr1-/-, Nrl-/-Arr4-/-, and Nrl-/-Arr1-/-Arr4-/- mice with photopic electroretinography (ERG) to assess light adaptation and retinal responses, immunoblot and immunohistochemical localization analysis to measure retinal expression levels of M- and S-opsin, and optokinetic tracking (OKT) to measure the visual acuity and contrast sensitivity.

RESULTS

Study results indicated that Nrl-/- and Nrl-/-Arr4-/- mice light adapted normally, while Nrl-/-Arr1-/- and Nrl-/-Arr1-/-Arr4-/- mice did not. Photopic ERG a-wave, b-wave, and flicker amplitudes followed a general pattern in which Nrl-/-Arr4-/- amplitudes were higher than the amplitudes of Nrl-/-, while the amplitudes of Nrl-/-Arr1-/- and Nrl-/-Arr1-/-Arr4-/- were lower. All three visual arrestin knockouts had faster implicit times than Nrl-/- mice. M-opsin expression is lower when ARR1 is not expressed, while S-opsin expression is lower when ARR4 is not expressed. Although M-opsin expression is mislocalized throughout the photoreceptor cells, S-opsin is confined to the outer segments in all genotypes. Contrast sensitivity is decreased when ARR4 is not expressed, while visual acuity was normal except in Nrl-/-Arr1-/-Arr4-/-.

CONCLUSIONS

Based on the opposite visual phenotypes in an all-cone retina in the Nrl-/-Arr1-/- and Nrl-/-Arr4-/- mice, we conclude that ARR1 and ARR4 perform unique modulatory roles in cone photoreceptors.

Dopamine receptor D4 internalization requires a beta-arrestin and a visual arrestin

PURPOSE

The G-protein coupled receptor (GPCR) Dopamine Receptor D4 (DRD4) plays an essential role in cAMP regulation and gap junctional coupling in the photoreceptors, where DRD4 expression is under circadian control. Previous in vitro transfection studies of human DRD4 desensitization have reported that DRD4 is not internalized upon dopamine stimulation when beta-arrestin is co-transfected with DRD4. We hypothesized that the visual arrestins, ARR1 and ARR4, play a modulatory role in DRD4 desensitization in the photoreceptors.

METHODS

To test this hypothesis, immunohistochemistry analysis of mouse retinas was used to determine the cellular localization of beta-arrestins and DRD4 in photoreceptors. In vitro studies were performed in HEK293T cells transiently transfected with human DRD4 and arrestins. First, co-immunoprecipitation experiments were executed to test protein-protein interactions and to investigate the effect of dopamine stimulation. Second, immunohistochemistry analysis was implemented to study DRD4 internalization and translocation of ARR4.

RESULTS

Immunohistochemistry studies of mouse retinas confirmed the expression of beta-arrestin 2, ARR1 and ARR4, as well as DRD4 in mouse cone photoreceptor inner segments. Co-immunoprecipitation experiments revealed a dopamine-dependent protein-protein interaction between human DRD4 and ARR4. In vitro internalization experiments showed that no detectable internalization of DRD4 was observed with any single arrestin co-transfected. However, a dopamine-dependent internalization of DRD4 was observed with three out of six sets of two arrestins co-transfected with DRD4. Each of these pairs of arrestins contained one visual arrestin and one beta-arrestin, and no internalization was observed with either two visual arrestins or two beta-arrestins. Additional time-course experiments revealed that in vitro, ARR4 translocates to co-localize with DRD4 at the plasma membrane in response to 30min of dopamine stimulation.

CONCLUSIONS

The results have functional implications and we hypothesize that the desensitization and internalization of DRD4 in photoreceptors are synergistically mediated by both visual and beta-arrestins. These results are additionally unique because they demonstrate for the first time that at least one G-protein coupled receptor, DRD4, requires two arrestins for desensitization and internalization, and opens up the possibility that other G-protein coupled receptors may require more than one arrestin for desensitization and/or internalization.

The expression of three opsin genes from the compound eye of Helicoverpa armigera (Lepidoptera: Noctuidae) is regulated by a circadian clock, light conditions and nutritional status

Visual genes may become inactive in species that inhabit poor light environments, and the function and regulation of opsin components in nocturnal moths are interesting topics. In this study, we cloned the ultraviolet (UV), blue (BL) and long-wavelength-sensitive (LW) opsin genes from the compound eye of the cotton bollworm and then measured their mRNA levels using quantitative real-time PCR. The mRNA levels fluctuated over a daily cycle, which might be an adaptation of a nocturnal lifestyle, and were dependent on a circadian clock. Cycling of opsin mRNA levels was disturbed by constant light or constant darkness, and the UV opsin gene was up-regulated after light exposure. Furthermore, the opsin genes tended to be down-regulated upon starvation. Thus, this study illustrates that opsin gene expression is determined by multiple endogenous and exogenous factors and is adapted to the need for nocturnal vision, suggesting that color vision may play an important role in the sensory ecology of nocturnal moths.

Circadian and noncircadian modulation of autophagy in photoreceptors and retinal pigment epithelium

PURPOSE

Autophagy in photoreceptors and the RPE promotes homeostasis and survival. The purpose of this study is to determine the daily pattern of changes in autophagy and factors contributing to its regulation in the outer retina.

METHODS

Levels of autophagy markers in the retina and RPE were evaluated over a 24-hour period. To assess the role of phagocytosis in stimulating autophagy in the RPE, cultured RPE-J cells were incubated with isolated photoreceptor outer segments and levels of autophagy markers were measured. Electron microscopy was performed on retina sections and RPE-J cells to assess formation of double-membraned vesicles consistent with autophagosomes.

RESULTS

In wild-type C57BL/6 mice maintained under normal cycling light conditions, autophagy in photoreceptor cells and the RPE exhibited a bimodal pattern of activation. In photoreceptors, shifts between light and dark evoked a sharp decrease in autophagy that was followed by a time-dependent increase. In photoreceptors, translocation of transducin and arrestin from the outer to inner segment appeared to contribute to the light-dependent upregulation of autophagy. In contrast, the cyclic variations in RPE autophagy were independent of lighting conditions, and are triggered, at least in part, by ingestion of outer segments.

CONCLUSIONS

Activation of autophagy in the outer retina exhibits a bimodal pattern that correlates with shifts in transduction proteins within the photoreceptor and by circadian ingestion of outer segments in the RPE. These dynamic shifts suggest a critical role for this pathway in maintaining homeostasis, with further study needed to define the mechanisms underlying the regulation of this phenomenon.

Cone arrestin: deciphering the structure and functions of arrestin 4 in vision

Cone arrestin (Arr4) was discovered 20 years ago as a human X-chromosomal gene that is highly expressed in pinealocytes and cone photoreceptors. Subsequently, specific antibodies were developed to identify Arr4 and to distinguish cone photoreceptor morphology in health and disease states. These reagents were used to demonstrate Arr4 translocation from cone inner segments in the dark to outer segments with light stimulation, similarly to Arrestin 1 (Arr1) translocation in rod photoreceptors. A decade later, the Arr4 crystal structure was solved, which provided more clues about Arr4's mechanisms of action. With the creation of genetically engineered visual arrestin knockout mice, one critical function of Arr4 was clarified. In single living cones, both visual arrestins bind to light-activated, G protein receptor kinase 1 (Grk1) phosphorylated cone opsins to desensitize them, and in their absence, mouse cone pigment shutoff is delayed. Still under investigation are additional functions; however, it is clear that Arr4 has non-opsin-binding partners and diverse synaptic roles, including cellular anchoring and trafficking. Recent studies reveal Arr4 is involved in high temporal resolution and contrast sensitivity, which opens up a new direction for research on this intriguing protein. Even more exciting is the potential for therapeutic use of the Arr4 promoter with an AAV-halorhodopsin that was shown to be effective in using the remaining cones in retinal degeneration mouse models to drive inner retinal circuitry for motion detection and light/dark discrimination.

The Antarctic krill Euphausia superba shows diurnal cycles of transcription under natural conditions

BACKGROUND

Polar environments are characterized by extreme seasonal changes in day length, light intensity and spectrum, the extent of sea ice during the winter, and food availability. A key species of the Southern Ocean ecosystem, the Antarctic krill (Euphausia superba) has evolved rhythmic physiological and behavioral mechanisms to adapt to daily and seasonal changes. The molecular organization of the clockwork underlying these biological rhythms is, nevertheless, still only partially understood.

METHODOLOGY/PRINCIPAL FINDINGS

The genome sequence of the Antarctic krill is not yet available. A normalized cDNA library was produced and pyrosequenced in the attempt to identify large numbers of transcripts. All available E. superba sequences were then assembled to create the most complete existing oligonucleotide microarray platform with a total of 32,217 probes. Gene expression signatures of specimens collected in the Ross Sea at five different time points over a 24-hour cycle were defined, and 1,308 genes differentially expressed were identified. Of the corresponding transcripts, 609 showed a significant sinusoidal expression pattern; about 40% of these exibithed a 24-hour periodicity while the other 60% was characterized by a shorter (about 12-hour) rhythm. We assigned the differentially expressed genes to functional categories and noticed that those concerning translation, proteolysis, energy and metabolic process, redox regulation, visual transduction and stress response, which are most likely related to daily environmental changes, were significantly enriched. Two transcripts of peroxiredoxin, thought to represent the ancestral timekeeping system that evolved about 2.5 billion years ago, were also identified as were two isoforms of the EsRh1 opsin and two novel arrestin1 sequences involved in the visual transduction cascade.

CONCLUSIONS

Our work represents the first characterization of the krill diurnal transcriptome under natural conditions and provides a first insight into the genetic regulation of physiological changes, which occur around the clock during an Antarctic summer day.

The expression of genes encoding visual components is regulated by a circadian clock, light environment and age in the honeybee (Apis mellifera)

The honeybee, Apis mellifera, has been used as a model to study the development of the visual system and adult bee behaviour. However, the regulation of the levels of visual component genes has never been addressed in this organism. We isolated honeybee cDNAs encoding green-sensitive opsin and visual arrestin and then measured their mRNA levels in honeybee workers. Both mRNAs fluctuate on a daily cycle that depends on a pacemaker that functions separately from the pacemaker which controls rhythmic locomotor activity. The cycling-patterns of opsin and arrestin mRNAs are different from each other and are modified by light. Furthermore, light exposure can increase the absolute levels of both mRNAs and the arrestin mRNA level is also dependent on age. Consistent with these results, both mRNA levels are higher in foragers than in in-hive bees under natural conditions. This study thus shows that the expression of genes encoding visual components is regulated by multiple factors and is adjusted to the honeybees' need for vision during the day, and throughout their lives. Comparison of data obtained with honeybees and other organisms indicates that there is a link between the regulation of phototransduction components and vision-related animal behaviour.

Light-driven translocation of the protein phosphatase 2A complex regulates light/dark dephosphorylation of phosducin and rhodopsin

In steps of protein purification of bovine retinal protein phosphatase 2A (PP2A), phosducin dephosphorylation activity peaks coelute with a PP2A enzyme complex, shown by peptide sequence analysis to contain a B' subunit, B56 epsilon. Other PP2A complexes with a slightly larger (56.5 kDa) B' subunit (sequenced to be B56 alpha) or with the B alpha regulatory subunit have no phosducin dephosphorylation activity. Upon exposure to light, a significant increase in the immunoreactive protein level of the A, C, and B56 epsilon PP2A subunits is observed in the cytosolic fraction of mouse retina, the phosducin dephosphorylation of which occurs rapidly. During dark exposure, these subunits translocate to the membrane fraction where rhodopsin is slowly dephosphorylated. This PP2A redistribution occurs in less than 1.5 min and is dependent upon light and not upon an intrinsic circadian rhythm. Forty times more of the A subunit (approximately 20 ng/mouse retina) and 9 times more of the C subunit (approximately 4 ng/mouse retina) than of the B56 epsilon subunit (approximately 0.45 ng/mouse retina) redistribute, which suggests that the predominant form of the PP2A enzyme complex on the membrane in the dark is a dimer, consisting of only A and C subunits. We observe that the dimer favors phosphorylated opsin as a substrate, while the trimer, particularly the enzyme complex with the B56 epsilon subunit, greatly prefers phosphorylated phosducin, with an activity several hundred times those of other substrates that were tested. This light-driven PP2A translocation provides a potential mechanism for efficient dephosphorylation of two critical photoreceptor transduction proteins, cytosolic phosducin and membrane-bound rhodopsin, by the same enzyme.

Mouse cone arrestin gene characterization: promoter targets expression to cone photoreceptors

Cone arrestin (CAR) is a novel member of the arrestin superfamily expressed in retinal cone photoreceptors and the pineal gland. To understand the regulatory mechanisms controlling its cone- and pineal-specific expression, and to facilitate further functional studies using gene knockout approaches, we characterized the genomic organization and the 5'-flanking region of the mouse CAR (mCAR) gene. The mCAR gene is comprised of 17 exons and 16 introns, encoding five alternatively spliced transcripts. A 215-bp proximal promoter fragment containing a TATA box, an Sp1 site and four cone-rod homeobox-binding sites is sufficient to direct expression in cultured retinoblastoma cells and in cone photoreceptors and the pineal gland in transgenic Xenopus laevis.

Modulation of CRX transactivation activity by phosducin isoforms

Phosducin (Phd) and Phd-like proteins (PhLPs) selectively bind guanine nucleotide protein (G protein) betagamma subunits (Gbetagamma), while Phd-like orphan proteins (PhLOPs) lack the major functional domain for the binding of Gbetagamma. A retina- and pineal gland-specific transcription factor, cone-rod homeobox (CRX), was identified by a yeast two-hybrid screen using PhLOP1 as the bait. Direct protein-protein interactions between Phd or PhLOP1 and CRX were demonstrated using a beta-galactosidase quantitative assay in the yeast two-hybrid system and were confirmed by an in vitro binding assay and a glutathione S-transferase (GST) pull-down assay. To determine if the interaction with Phd or PhLOP1 affected CRX transactivation, a 120-bp interphotoreceptor retinoid binding protein (IRBP) promoter-luciferase reporter construct containing a CRX consensus element (GATTAA) was cotransfected into either COS-7 or retinoblastoma Weri-Rb-1 cells with expression constructs for CRX and either Phd or PhLOP1. Phd and PhLOP1 inhibited the transcriptional activation activity of CRX by 50% during transient cotransfection in COS-7 cells and by 70% in Weri-Rb-1 cells and COS-7 cells stably transfected with CRX. Phd inhibited CRX transactivation in a dose-dependent manner. Whereas Phd is a cytoplasmic phosphoprotein, coexpression of Phd with CRX results in Phd being localized both in the cytoplasm and nucleus. By contrast, PhLOP1 is found in the nucleus even without CRX coexpression. To address the physiological relevance of these potential protein interacting partners, we identified immunoreactive proteins for Phd and CRX in retinal cytosolic and nuclear fractions. Immunohistochemical analysis of bovine retinas reveals colocalization of Phd isoforms with CRX predominantly in the inner segment of cone cells, with additional costaining in the outer nuclear layer and the synaptic region. Our findings demonstrate that both Phd and PhLOP1 interact directly with CRX and that each diminishes the transactivation activity of CRX on the IRBP promoter. A domain that interacts with CRX is found in the carboxyl terminus of the Phd isoforms. Phd antibody-immunoreactive peptides are seen in light-adapted mouse retinal cytosolic and nuclear extracts. Neither Phd nor PhLOP1 affected CRX binding to its consensus DNA element in electrophoretic mobility shift assays. A model that illustrates separate functional roles for interactions between Phd and either SUG1 or CRX is proposed. The model suggests further a mechanism by which Phd isoforms could inhibit CRX transcriptional activation.

Identification of specific histidine residues and the carboxyl terminus are essential for serotonin N-acetyltransferase enzymatic activity

Melatonin is synthesized in pinealocytes of the pineal gland and in photoreceptors of the retina. Synthesis rate from serotonin to melatonin is controlled by the rapid and dramatic enzymatic increase in darkness of serotonin N-acetyltransferase (arylalkylamine N-acetyltransferase, AA-NAT, EC 2.3.1.87) and hydroxyindole-O-methyltransferase (HIOMT, EC 2.1.1.4). The primary structure of these critical indoleamine enzymes is now known and the regulation of the enzyme catalysis can be examined. As a first step, the conserved cysteine (C) and histidine (H) residues were targeted for site-directed mutagenesis as potential amino acid residues involved in the N-acetylation reaction of AA-NAT. Our studies concluded that among 6 histidine (H) to alanine (A) mutations, three residues (H110A, H118A, H120A) within the AA-NAT protein showed little or no enzymatic activity, whereas the others (H28A, H70A, H125A) retained enzymatic activity, compared to the unaltered AA-NAT protein. Cysteine to alanine mutations, C37A and C177A, had no significant effect on the AA-NAT enzymatic activity; however, C61A had a four-fold increase in K(m) for acetyl CoA and an altered sensitivity to the thiol modification chemical, N-ethylmaleimide (NEM), implying that C61 may participate in the acetyl CoA binding. Further studies examined the AA-NAT enzyme regulation of the highly conserved carboxyl terminus. When 12 terminal amino acid residues were deleted systematically from the carboxyl terminus of the 205 amino acid residue AA-NAT protein, enzyme activity was retained. However, further residue deletion resulted in enzyme activity plummeting, implicating that the essential information either for the correct structural folding into an active enzyme form or for enzyme stability is in the 193 residues. To test the relative importance of the AA-NAT carboxyl terminal region, a single leucine (L) was altered to alanine (A) or proline (P). Both mutants, either L193A or L193P, had a marked decrease in AA-NAT enzymatic activity and a decrease in thermal stability, suggesting the leucine, in addition to the cysteine and histidine residues, is involved in either enzyme catalysis or stability. In light of the recently reported three-dimensional structure of AA-NAT (17,18), the site-directed mutagenesis data demonstrate experimentally the importance of essential amino acid residues for acetyl CoA binding and AA-NAT activation.

Circadian oscillation of photopigment transcript levels in the mouse retina

The mammalian retina contains an autonomous circadian oscillator that can sustain rhythms in outer segment disc shedding and melatonin synthesis even in the absence of cues from the central oscillator in the suprachiasmatic nucleus (SCN). The present investigation aimed to ascertain whether the steady-state levels of rod and cone opsin mRNA exhibited a circadian oscillation in the mouse, and if so, to characterise this oscillation with regard to phase. Retinas were collected from mice free-running in constant darkness at circadian times (CT) 0, 4, 12, 16, and 20. RNA was extracted for the production of Northern blots, which were sequentially hybridised with probes for alpha-tubulin (control), ultraviolet opsin, and rhodopsin. Whereas no significant oscillation was detected in the levels of alpha-tubulin, the levels of both ultraviolet opsin and rhodopsin transcripts oscillated with an amplitude of at least 3-fold. The highest levels were found at around CT12 (which corresponds to the subjective evening, the time of activity onset in the mouse). These results show that the levels of rod and cone photopigment mRNA are under circadian control. The significance of the rhythms and their phasing is discussed. These findings have potential clinical implications both with regard to nocturnal light treatment of phase asynchrony, and in the timing of chemo- and radiotherapy.

Biochemical characterization of recombinant serotonin N-acetyltransferase

Pineal and retinal melatonin synthesis is controlled by the enzymatic activity of arylalkylamine N-acetyltransferase (AA-NAT, EC 2.3.1.87), which is regulated by light/dark signals and circadian factors. This enzyme converts serotonin to N-acetylserotonin by the transfer of an acetyl group from acetyl coenzyme A. Endogenous AA-NAT instability during routine purification has made enzyme characterization difficult, but now a stable recombinant protein for AA-NAT has been synthesized to investigate the intrinsic biochemical properties of AA-NAT from a rat pineal cDNA encoding a 205 amino acid, 23 kilodalton protein, by using a glutathione-S-transferase (GST) fusion protein system. Recombinant GST-AA-NAT showed substrate specificity for arylalkylamines and stability at 4 degrees C; however, the enzyme activity was reduced by 40% upon preincubation at 37 degrees C for 2 hr. GST-AA-NAT is preferentially phosphorylated by either cyclic AMP- or cyclic GMP-dependent kinases in vitro, but no detrimental effect was observed on AA-NAT enzymatic activity. Among the metal cations tested in this study, Ca2+, Mg2+, Mn2+, Fe2+, and Co2 showed little or no inhibitory potency, while either 1 mM Zn2+ or 0.1 mM Cu2+ nearly abolished the enzymatic activity. GST-AA-NAT enzyme activity is also inhibited by reagents that are known biochemically to modify thiol groups (N-ethylmaleimide, NEM) and histidine residues (p-chloromercuribenzoate, NBS and diethyl pyrocarbonate, DEPC), suggesting the presence of essential cysteine and histidine moieties. Moreover, preincubation of acetyl CoA completely protects the recombinant AA-NAT from inactivation by NEM and DEPC, indicating that specific cysteine and histidine residues may be at the acetylation site. The conclusion is that the biochemical properties of rat recombinant AA-NAT is similar to the endogenous pineal and retinal AA-NAT with respect to the sensitivity to temperature, metal cations, as well as the thiol modification reagents. These data also suggest that the phosphorylation status of the AA-NAT does not affect enzymatic activity directly, and histidine residues are potentially important residues required for high catalytic activity.

Photoreceptor function of retinal transplants implicated by light-dark shift of S-antigen and rod transducin

The aim was to demonstrate functional properties of transplanted histologically normal photoreceptors. Subretinal intact-sheet transplants of fetal E17-E20 rat retinas to light-damaged albino rat eyes were fixed in light or dark, 2 to 42 weeks after transplantation, and stained immunohistochemically for certain phototransduction proteins. In light adapted transplants, transducin was predominantly found in inner segments of parallel-organized photoreceptors. Transducin shifted to the outer segments with dark-adaptation. S-antigen distribution was opposite to transducin. Rhodopsin distribution did not change. The shift of signal transduction proteins correlated to the light conditions indicates that normal phototransduction processes were established in photoreceptors of transplanted retinal sheets.

Immediate upstream sequence of arrestin directs rod-specific expression in Xenopus

Arrestins are a family of proteins that modulate G protein-coupled receptor responses with distinct arrestin genes expressed in rods and cones. To understand the regulatory mechanisms controlling rod-specific expression, the abundant Xenopus rod arrestin cDNA and a partial genomic clone, containing the immediate upstream region and amino terminus of the polypeptide, have been characterized. The deduced polypeptide has approximately 69% identity to other vertebrate rod arrestins. Southern blot analysis and polymerase chain reaction of intronic sequences demonstrated multiple alleles for rod arrestin. DNase I footprinting with retinal proteins revealed four major DNA binding sites in the proximal promoter, coinciding with consensus sequences reported in mammalian promoters. Purified bovine Crx homeodomain and mouse Nrl proteins protected a number of these sites. A dual approach of transient embryo transfections and transgenesis was used to locate transcriptional control sequences essential for rod-specific expression in Xenopus. Constructs containing -1287/+113 of 5' upstream sequence with or without intron 1 directed high level expression, specifically in rods. A construct containing only -287/+113 directed expression of green fluorescent protein solely in rod cells. These results suggest that the Crx and Nrl binding sites in the proximal promoter are the primary cis-acting sequences regulating arrestin gene expression in rods.

Bovine arylalkylamine N-acetyltransferase activity correlated with mRNA expression in pineal and retina

Arylalkylamine N-acetyltransferase (AA-NAT, E. C. 2.3.1.87) is the enzyme that catalyzes the transfer of an acetyl group from acetyl-CoA to serotonin to form N-acetylserotonin (NAS) in the indoleamine biosynthetic pathway. Bovine pineal AA-NAT, partially purified on an anion exchange column, displayed an 8-fold higher enzymatic activity in pineals from animals killed in early morning (0800) compared to an afternoon group (1430). Poly A(+) mRNA was isolated from early morning bovine pineals, used to construct a mammalian expression cDNA library (lambdaZAP Express), and then screened with a rat AA-NAT cDNA to isolate a 924 basepair cDNA that encodes the bovine pineal AA-NAT. The amino acid sequence alignment reveals that bovine AA-NAT shares 94.20%, 78.54%, 76.33% and 56.3% identity to ovine, rat, human and chicken sequences, respectively. Northern blot analysis demonstrates a 0.7-fold higher mRNA level in pineal glands taken from animals from the 0800 time-point compared with mRNA from the 1430 time-point. AA-NAT mRNA was expressed at high levels in pineal and retina, but the message was undetectable in adrenal, cerebellum, cortex, small intestine, testis and thyroid. Based on the significant identity of amino acid sequence and the similar mRNA expression pattern, these data suggest that the bovine AA-NAT is more analogous to the ovine rather than either the rat, human or chicken AA-NAT.

PhLPs and PhLOPs in the phosducin family of G beta gamma binding proteins

In this study, we identify new isoforms of the retinal phosducin and investigate the expression of the phosducin family, showing that an isoform, PhLP1, has sequence homology with Phd and Gbeta gamma binding capability, whereas two isoforms (phosducin-like orphan proteins, PhLOPs) share sequence homology with Phd but fail to bind Gbeta gamma. Original identification of PhLP1 and the PhLOPs was from a human retina cDNA library, using a PCR product for library hybridization screening that contained a predicted functional epitope domain. The screen identified Phd and three related, but distinct, recombinants (PhLP1, PhLOP1, and PhLOP2). By RT-PCR, all isoforms are expressed in either retina or forskolin-stimulated Y79 retinoblastoma cells; however, the new isoforms are below the level of detection on Northern blot analysis. The predicted amino acid translation of each homologue revealed major differences, arising from either splice variants or gene duplication of Phd. To test the functional interaction of all phosducin isoforms with Gbeta gamma in vitro, a glutathione S-transferase (GST) fusion protein was developed for each member. Biochemical interaction with purified retinal transducin Gbeta gamma was verified for GST-Phd and demonstrated for GST-PhLP1; however, neither GST-PhLOP1 nor GST-PhLOP2 bound Gbeta gamma. Comparable results were observed when the GST-phosducin fusion proteins selectively sequestered Gbeta gammas from retinal extracts or when functional Gbeta gamma interactions were assessed using surface plasmon resonance technology. Phosducin and its isoforms are widely distributed in body tissues where they may participate in signal transduction pathways. Phd and PhLP1 possess an 11-amino acid conserved epitope domain (TGPKGVINDWR) that controls the high-affinity binding of Gbeta gamma; these isoforms are implicated in the G-protein signaling pathway. The phosducin-like orphan proteins (PhLOPs) fail to bind Gbeta gamma, suggesting that the PhLOP isoforms may participate in still unidentified signaling pathways.

Developmental expression pattern of phototransduction components in mammalian pineal implies a light-sensing function

Whereas the pineal organs of lower vertebrates have been shown to be photosensitive, photic regulation of pineal function in adult mammals is thought be mediated entirely by retinal photoreceptors. Extraretinal regulation of pineal function has been reported in neonatal rodents, although both the site and molecular basis of extraretinal photoreception have remained obscure. In this study we examine the developmental expression pattern of all of the principal components of retinal phototransduction in rat pineal via cRNA in situ hybridization. All of the components needed to reconstitute a functional phototransduction pathway are expressed in the majority of neonatal pinealocytes, although the expression levels of many of these genes decline dramatically during development. These findings strongly support the theory that the neonatal rat pineal itself is photosensitive. In addition, we observe in neonatal pinealocytes the expression of both rod-specific and cone-specific phototransduction components, implying the existence of functionally different subtypes of pinealocytes that express varying combinations of phototransduction enzymes.

Microglia in the pineal gland of the neonatal rat: characterization and effects on pinealocyte neurite length and serotonin content

Microglia in the pineal gland of 1-day-old Sprague-Dawley rats were examined by OX-42 immunocytochemistry and DiI-acetylated-LDL uptake in pineal cell suspension and were found to comprise 3-5% of the total cells in the pineal gland of the neonates. In order to investigate the effects of microglia on pinealocyte structure and function, microglia-depleted and microglia-enriched pineal cell cultures were generated from 1-day-old neonate by fluorescence activated cell sorting (FACS). After 7 days of culture, tissues were processed for either immunocytochemistry for pinealocyte S-antigen and serotonin or high performance liquid chromatography to measure serotonin. Morphometric analysis of immunoreacted cells revealed that pinealocyte neurite length was enhanced in microglia-depleted cultures and was inhibited in a microglia-enriched environment (ANOVA, P < 0.001). Serotonin content of pineal cultures decreased in microglia-depleted cultures and was elevated in microglia-enriched cultures (ANOVA, P < 0.001) without any significant change in pinealocyte numbers. These findings are consistent with a working hypothesis that microglia function to mediate neuroendocrine-immune interactions of the gland.

Diurnal expression of recoverin in the rat retina

The levels of expression of recoverin mRNA and protein was examined during a 24-h period in the rat retina. Northern blot analysis revealed that rat recoverin mRNA expression was consistently high during the light period, then decreased after onset of darkness, and gradually increased later during the dark period. The cyclic rhythm in recoverin protein expression was consistent with the cyclic rhythm in recoverin mRNA expression, insofar as recoverin mRNA and protein levels were lowest soon after lights off, and there was an increase in expression late in the dark period. These observations suggest that the rate of recoverin transcription may occur maximally during the period of greatest exposure to light, presumably when it is most needed by the photoreceptor to fulfill its role in visual transduction, then decreases at night, when high levels of expression are not required.

Light-mediated retinoic acid production

Retinoids serve two main functions in biology: retinaldehyde forms the chromophore bound to opsins, and retinoic acid (RA) is the activating ligand of transcription factors. These two functions are linked in the vertebrate eye: we describe here that illumination of the retina results in an increase in RA synthesis, as detected with a RA bioassay and by HPLC. The synthesis is mediated by retinaldehyde dehydrogenases which convert some of the chromophore all-trans retinaldehyde, released from bleached rhodopsin, into RA. As the eye contains high levels of retinaldehyde dehydrogenases, and as the oxidation of retinaldehyde is an irreversible reaction, RA production has to be considered an unavoidable by-product of light. Through RA synthesis, light can thus directly influence gene transcription in the eye, which provides a plausible mechanism for light effects that cannot be explained by electric activity. Whereas the function of retinaldehyde as chromophore is conserved from bacteria to mammals, RA-mediated transcription is fully evolved only in vertebrates. Invertebrates differ from vertebrates in the mechanism of chromophore regeneration: while in the invertebrate visual cycle the chromophore remains bound, it is released as free all-trans retinaldehyde from illuminated vertebrate rhodopsin. RA synthesis occurring as corollary of dark regeneration in the vertebrate visual cycle may have given rise to the expansion of RA-mediated transcriptional regulation.

Circadian regulation of hydroxyindole-O-methyltransferase mRNA levels in rat pineal and retina

Hydroxyindole-O-methyltransferase (HIOMT, EC 2.1.1.4) catalyzes the methylation of acetylserotonin to complete the synthesis of melatonin in the pineal and retina. A complete 1728 nucleotide cDNA encoding rat pineal HIOMT was isolated, characterized, and used to evaluate day/night levels of HIOMT mRNA. As previously reported for HIOMT enzyme activity, HIOMT mRNA levels were also greater in the pineal than in the retina. Northern blot analysis and in situ hybridization were useful for detection of HIOMT mRNA in the pineal but not the retina, whereas the reverse transcriptase-polymerase chain reaction or RNase protection assay revealed transcripts for HIOMT both in the pineal and retina. Investigating HIOMT mRNA levels in rat pineal and retina at 6 time-points throughout a 24 h period revealed higher levels of HIOMT message during darkness. The daily fluctuation in HIOMT mRNA persisted in constant darkness, verifying an endogenous circadian rhythm both in the pineal and retina. In mammalian pineals, sympathetic innervation, synthesizing norepinephrine that activates beta (beta) adrenergic receptors, entrain several circadian bodily functions through the synthesis and release of melatonin. A single injection of the beta-adrenergic agonist, isoproterenol, induced a dramatic increase of HIOMT mRNA levels in the light-adapted pineal, in vivo. Moreover, a single injection of the beta-adrenergic antagonist, propranolol, prevented the nocturnal increase of pineal HIOMT mRNA. Using a combination of methods, it has been shown that the level of HIOMT mRNA fluctuates daily in both the pineal gland and retina. This day/night rhythm can be modulated either by beta receptor agonists or antagonists when applied appropriately during the circadian cycle, suggesting that the mRNA changes in HIOMT may be controlled at the transcriptional level.

Hydroxyindole-O-methyltransferase in the chicken retina: immunocytochemical localization and daily rhythm of mRNA

In the vertebrate retina and pineal gland, melatonin production displays diurnal variations with high levels at night. Hydroxyindole-O-methyltransferase (HIOMT, EC 2.1.1.4) catalyses the last step of melatonin biosynthesis. In the present study, a cDNA encoding chicken HIOMT was used to examine the effects of environmental lighting on HIOMT mRNA expression in the chicken retina. A day/night rhythm of HIOMT mRNA level was observed, with an average 5-fold increase during the night. Light strongly suppressed the night-time rise in HIOMT mRNA concentration while darkness prevented its daytime fall. An antibody directed against chicken HIOMT was used for immunocytochemical identification of retinal melatoninergic cells. HIOMT immunoreactivity could be observed in rods as well as in cones. However, the lowest levels of HIOMT immunoreactivity were always observed in the accessory cones of double cones. A few HIOMT-positive cell bodies could also be observed in the inner nuclear layer. Altogether, these data indicate that HIOMT gene expression in the retina is organized on a daily basis as a direct response to light, and that the different types of photoreceptors may not be equally involved in melatonin production.

The arrestin superfamily: cone arrestins are a fourth family

Arrestins constitute a superfamily of regulatory proteins that down-regulate phosphorylated G-protein membrane receptors, including rod and cone photoreceptors and adrenergic receptors. The potential role of arrestin in color visual processes led us to identify a cDNA encoding a cone-like arrestin in Xenopus laevis, the principle amphibian biological model system. Alignment of 18 deduced amino acid sequences of all known arrestins from both invertebrate and vertebrate species reveals five arrestin families. Further analysis identifies 7 variable and 4 conservative arrestin structural motifs that may identify potential functional domains. The adaptive evolutionary relationship of Xenopus cone arrestin to the arrestin gene tree suggests high intrafamily homology and early gene duplication events.

Identification of circadian gene expression in the rat pineal gland and retina by mRNA differential display

To identify unique gene products that could be crucial for circadian and light-dark regulations, using the technology of differential display, we have investigated mRNAs that were isolated from rat pineals and retinas collected either during subjective day (D) or subjective night (N). A subpopulation of about 50 mRNAs were amplified from pineal using designed primers and reverse transcriptase-polymerase chain reaction. Thirty five of the mRNAs were expressed equivalently in both D and N samples. From the 15 mRNAs showing differential expression, four amplified products were selected, based on higher expression during the subjective night (N310, N320, N383, N420) and each was subcloned and sequenced. Of the four cDNAs studied, only N310 was determined to have significant identity to a known cell adhesion protein, called F3. This protein is highly expressed in developing mouse neurons and is related to chicken contactin. Each differentially displayed product identified is being examined further in order to understand their potential significance in the circadian regulation of pineal and retinal activities.

Immunochemical evaluation of S-antigen of rabbit pineal gland

Purified S-antigen of photoreceptor cells induces experimental autoimmune uveoretinitis (EAU) and experimental autoimmune pinealitis (EAP) in laboratory animals. However, in rabbits, S-antigen induces only EAU without EAP. To evaluate this difference, the authors studied immunochemical reactivity of rabbit pineal gland with a panel of anti-S-antigen monoclonal antibodies (MAb). Rabbit pineal gland reacted with the MAbs by ELISA and immunoblot but not by immunohistochemistry. In contrast, rabbit retina like guinea pig retina, guinea pig pineal gland and bovine retina reacted with these MAbs by immunohistochemistry as well as by ELISA and immunoblot. Also, S-antigen purified from rabbit retina reacted as did bovine and guinea pig S-antigen. Therefore, S-antigen in situ in rabbit pineal gland is different from S-antigen of rabbit retina and different from S-antigen of pineal gland and retina of other species. Just as the MAbs did not react with S-antigen in rabbit pineal gland, it is possible that S-antigen activated lymphocytes may not recognize S-antigen in rabbit pineal gland and thereby not induce EAP.

The molecular basis for winter depression

A pulse of light is capable of inducing the circadian phase-dependent gene expression in neurons. The phase or amplitude of the circadian rhythms can be modulated by critically timed exposures to light. A significant heritability for the light-induced responses has been observed in hamsters. In humans, light has been used for treatment of the light-dependent winter depressive disorder. A genetic predisposition for high responsiveness to light may occur in patients with winter depression. The altered gene expression induced by light may account for a unique sensitivity to light and mediate the anti-depressant effect of light treatment.

Light-dependent regulation of the transcriptional activity of the mammalian gene for arrestin

The purpose of this investigation was to determine if the cyclic variations in the amount of arrestin mRNA that occur in the mouse retina during the light/dark cycle are controlled by light, a circadian clock, or both. In this study, an experimental paradigm was designed and used to distinguish among these molecular mechanisms. The data show that the initiation and the maintenance of an increased rate of syntheses of arrestin mRNA requires light and is not dependent on the time of day. Therefore the changes in transcriptional activity of the mouse arrestin gene are controlled by light, independent of circadian clock. The mechanism for this light-dependent regulation of gene transcription in the retina is distinct from the light-dependent increases in mRNA concentrations of early response genes which occur in the suprachiasmatic nucleus and a comparative analysis of such changes in these different regions of the CNS may lead to the identification of the molecular relationship between light- and circadian-dependent gene regulation.

Alterations in light-evoked dopamine metabolism in dystrophic retinas of mutant rds mice

In dystrophic retinas of rds mice, which are devoid of photoreceptor outer segments, high steady state levels of dopamine were found in dark and light periods. These levels were similar to those observed in normal, BALB/c mouse retinas. Major differences were determined, however, between dopamine turnover in normal and dystrophic retinas. While substantial light-evoked elevation of dopamine synthesis and utilization was observed in normal retinas, dopamine synthesis and metabolism in rds retinas was very low and response to light was depressed. Retinal dopamine metabolism was already depressed in 2 week old rds mice, prior to the onset of photoreceptor cell death, relative to that in age-matched BALB/c mice. At 1 month of age, robust light/dark differences in retinal dopamine metabolism were observed in BALB/c mice, while no significant effect of light was seen in rds mice. The limited ability of the dopaminergic system in rds retinas to respond to light may be due to the absence of normal outer segments. Interestingly, in old rds retinas, although most photoreceptor cells had degenerated, a small but significant light-evoked increase in dopamine metabolism was measured. The presence of relatively high steady state levels of dopamine in rds retinas, despite the reduced dopamine synthetic activity, is maintained by a compensatory reduction in dopamine utilization. Thus, although a considerable amount of dopamine is present in the rds retina, it might not be available to exert its biological functions.

Tryptophan hydroxylase expression is regulated by a circadian clock in Xenopus laevis retina

A circadian clock has been localized to the photoreceptor layer in the Xenopus laevis retina. This clock controls the rhythmic synthesis of melatonin, which results in elevated levels during the night and low levels during the day. The rate-limiting enzyme in melatonin synthesis in Xenopus laevis retina is tryptophan hydroxylase. A cDNA clone coding for Xenopus tryptophan hydroxylase was isolated, characterized, and used as a probe for analysis of tryptophan hydroxylase mRNA expression. Northern blot analyses of total retinal RNA show that the tryptophan hydroxylase message levels are low in the day and higher at night. The expression of tryptophan hydroxylase mRNA is under circadian control because rhythmic changes are also seen in constant darkness, with elevated levels during the subjective night. Nuclear run-on analysis during the first subjective day in constant darkness revealed that transcription initiation is low early in the day and increases throughout the day. Our observations suggest that the circadian clock modulates tryptophan hydroxylase gene expression. An understanding of how the circadian clock controls tryptophan hydroxylase expression may lead to a clearer understanding of the melatonin biosynthetic pathway, and possibly the clock itself.

Effect of hydroxylamine on the subcellular distribution of arrestin (S-antigen) in rod photoreceptors

The immunocytochemical labeling of arrestin (S-antigen) in photoreceptors of the ovine retina was examined following incubation of the retina with hydroxylamine (NH2OH), an agent known to inhibit the phosphorylation of photoactivated rhodopsin. Intact, isolated retinas bathed in medium containing 20 mM NH2OH, or in control medium lacking NH2OH, were maintained in darkness or exposed to bright light for 3 min (dark-adapted and light-adapted conditions, respectively); further incubated in darkness for 10 min; and then fixed and prepared for cryosectioning. Cryosections were incubated with anti-S-antigen monoclonal antibody MAb A2G5; with secondary antibodies that were conjugated with horseradish peroxidase; and with either 3-amino-9-ethyl carbazole or diaminobenzidine as chromogen. Anti-arrestin labeling in cryosections was then analyzed densitometrically using a light-microscopic image processing system. In dark-adapted control retinas, labeling density of the photoreceptor outer segment (OS) layer (0.061 +/- 0.004; average +/- S.E.M.) was less than that of the inner segment (IS) layer (0.138 +/- 0.011). In light-adapted control retinas, OS labeling density (0.139 +/- 0.007) exceeded IS labeling density (0.095 +/- 0.005). Incubation with NH2OH eliminated this light-dependent increase in labeling of the OS relative to that of the IS, i.e. eliminated the increase in relative OS/IS labeling. Densities of labeling were 0.110 +/- 0.006 (OS) and 0.183 +/- 0.006 (IS) in NH2OH-treated dark-adapted retinas vs. 0.078 +/- 0.004 (OS) and 0.182 +/- 0.008 (IS) in NH2OH-treated light-adapted retinas. Anti-arrestin labeling was also examined in retinas that were exposed to 3 min or 13 min of bright light and then immediately fixed.(ABSTRACT TRUNCATED AT 250 WORDS)

Diurnal expression of NGF1-A mRNA in retinal degeneration slow (rds) mutant mouse retina

The retinal degeneration slow (rds) mutant mouse is a model for studying the retinal dystrophy for human disease, retinitis pigmentosa (RP). To continue our effort towards a possible mechanism of photoreceptor cell death in retinal dystrophies, we have studied the impact of the rds mutation on diurnal expression of a 'zinc-finger' DNA-binding protein, NGF1-A mRNA in the isolated retinas of rds mutant mice compared to those of BALB/c mice. Background levels of NGF1-A mRNA were maintained during the subjective light period. Higher levels of NGF1-A mRNA were observed immediately after the light offset and peaked two hours into the light offset for both the BALB/c and the rds mutant retinas and remained higher for several hours in the dark. If the animals were left continuously in light during the subjective dark period, NGF1-A mRNA levels were not induced and remained lower. On the other hand NGF1-A mRNA levels were transiently induced during the transition of the dark-to-light phase. The data suggest that NGF1-A mRNA is differentially regulated by light and dark stimuli in the retina and an absence of rod outer segments in the rds mutant retina does not alter the normal diurnal cycle of NGF1-A mRNA expression.

NonO, a non-POU-domain-containing, octamer-binding protein, is the mammalian homolog of Drosophila nonAdiss

We have cloned the ubiquitous form of an octamer-binding, 60-kDa protein (NonO) that appears to be the mammalian equivalent of the Drosophila visual and courtship song behavior protein, no-on-transient A/dissonance (nonAdiss). A region unprecedently rich in aromatic amino acids containing two ribonuclear protein binding motifs is highly conserved between the two proteins. A ubiquitous form of NonO is present in all adult tissues, whereas lymphocytes and retina express unique forms of NonO mRNA. The ubiquitous form contains a potential helix-turn-helix motif followed by a highly charged region but differs from prototypic octamer-binding factors by lacking the POU DNA-binding domain. In addition to its conventional octamer duplex-binding, NonO binds single-stranded DNA and RNA at a site independent of the duplex site.

NonO, a non-POU-domain-containing, octamer-binding protein, is the mammalian homolog of Drosophila nonAdiss

We have cloned the ubiquitous form of an octamer-binding, 60-kDa protein (NonO) that appears to be the mammalian equivalent of the Drosophila visual and courtship song behavior protein, no-on-transient A/dissonance (nonAdiss). A region unprecedently rich in aromatic amino acids containing two ribonuclear protein binding motifs is highly conserved between the two proteins. A ubiquitous form of NonO is present in all adult tissues, whereas lymphocytes and retina express unique forms of NonO mRNA. The ubiquitous form contains a potential helix-turn-helix motif followed by a highly charged region but differs from prototypic octamer-binding factors by lacking the POU DNA-binding domain. In addition to its conventional octamer duplex-binding, NonO binds single-stranded DNA and RNA at a site independent of the duplex site.

Diurnal expression of c-fos in the mouse retina

The diurnal levels of c-fos mRNA were studied in the mouse retinas by means of RNA blot analysis. Mice were kept on a 12/12 h dark/light cycle and gene expression was studied at various time points during the day and night periods. The highest levels of c-fos mRNA were measured during the first half of the night period. The high levels persisted for about 4-5 h. The c-fos mRNA levels declined during the second half of the night period and remained low during the day period. Continuous illumination of mice during the first hours of the night period prevented the increase in c-fos mRNA. If mice were kept in the dark during the day period, they failed to show an increase in c-fos mRNA levels in the subsequent night period. Hence, following activation of c-fos during the night period, a refractory period exists at which illumination is required before c-fos can be induced again by dark. Although light appears to suppress the activation of c-fos in the night period, a short lived burst in c-fos expression of 30-60 min in duration was observed when dark-adapted animals were illuminated, either at the transition between the dark and light period or during the dark period. Thus, it appears that c-fos is activated in at least two different cell types in the retina which respond differently to light and dark stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunocytochemical demonstration of nerve growth factor (NGF) receptor in the pineal gland: effect of NGF on pinealocyte neurite formation

Nerve growth factor receptor immunoreactivity (NGFRI) in the pineal gland was examined both light and electron microscopically using the monoclonal antibody 192IgG. NGFRI was located on sympathetic fibers and on perivascular cells resembling macrophage/microglia. A pineal gland dispersed cell culture model confirmed the presence of NGFRI in cells that exhibited processes of varying lengths and were distributed among pinealocytes and other flat cells. Pinealocytes in dispersed cell culture were identified immunocytochemically by their expression of S-antigen, their round shape and small size and their tendency to extend neurites in the direction of the flat cells in culture. The length of pinealocyte neurites showed a significant increase when cultured in the presence of NGF (25 ng/ml), suggesting that trophic factors, mediated by these macrophage/microglial cells, are important to the morphogenesis of these neuroendocrine cells. Neurotrophic activation of these neuroendocrine macrophage/microglia may have neuro-immunomodulatory implications leading to expression of proteins encoded by the major histocompatibility complex.

Experimental autoimmune pinealitis in the rat: ultrastructure and quantitative immunocytochemical characterization of mononuclear infiltrate and MHC class II expression

Lewis rats immunized with Peptide M (an oligopeptide epitope of the S-antigen protein) developed experimental autoimmune uveoretinitis (EAU) and experimental autoimmune pinealitis (EAP). Temporal changes in mononuclear infiltrate to the pineal gland were quantitated by computer image analysis of sections immunostained with monoclonal antibodies to specific mononuclear populations. T helper/inducer cells (W3/25+) and monocyte/macrophages (OX-42+) were elevated during the early phases of inflammation (day 15) while cytotoxic/suppressor T cells (OX-8+) were elevated at days 15 and 21. Expression of MHC class II (OX-6) was markedly enhanced on pineal glia, but was not present on vascular endothelia during EAP. Ultrastructurally, many capillaries exhibited thickenings of the endothelia and basal lamina. EAP had little effect on the fine structure of pinealocytes and glia and there was little evidence of cellular destruction by day 21, in contrast to the extensive retinal destruction resulting from EAU. These findings suggest fundamental differences between EAU and EAP related to mechanisms of antigen processing/recognition in autoimmune diseases. Our study further indicates the importance of EAP as a model to investigate neuroendocrine-immune interactions.

Immunocytochemistry and calcium cytochemistry of the mammalian pineal organ: A comparison with retina and submammalian pineal organs

Morphologically the mammalian pineal organ is a part of the diencephalon. It represents a neural tissue histologically ("pineal nervous tissue") and is dissimilar to endocrine glands. Submammalian pinealocytes resemble the photoreceptor cells of the retina, and some of their cytologic characteristics are preserved in the mammalian pinealocytes together with compounds demonstrable by cyto- and immunocytochemistry and participating in photochemical transduction. In our opinion, the main trend of today's literature on pineal functions--only considering the organ as a common endocrine gland--deviates from this structural and histochemical basis. In mammals, similar to the lower vertebrates, the pinealocytes have a sensory cilium developed to a different extent. The axonic processes of pinealocytes form ribbon-containing synapses on secondary pineal neurons, and/or neurohormonal terminals on the basal lamina of the surface of the pineal nervous tissue facing the perivascular spaces. Ribbon-containing axo-dendritic synapses were found in the rat, cat, guinea pig, ferret, and hedgehog. In the cat, we found GABA-immunoreactive interneurons, while the secondary nerve cells, whose axons enter the habenular commissure, were GABA-immunonegative. GABA-immunogold-labeled axons run between pinealocytes and form axo-dendritic synapses on intrapineal neurons. There is a similarity between the light and electron microscopic localization of Ca ions in the mammalian and submammalian pineal organs and retina of various vertebrates. Calcium pyroantimonate deposits--showing the presence of Ca ions--were found in the outer segments of the pineal and retinal photoreceptors of the frog. In the rat and human pineal organ, calcium accumulated on the plasmalemma of pinealocytes and intercellularly among pinealocytes. The formation of pineal concrements in mammals may be connected to the high need for Ca exchange of the pinealocytes for their supposed receptor and effector functions.

Transient, cyclic changes in mouse visual cell gene products during the light-dark cycle

Temporal and spatial changes in the cellular and subcellular concentrations of photoreceptor cell gene products appear to be important features of phototransduction in rod photoreceptor cells. The time course of the rapid, light-dependent movement of S-antigen (S-Ag) (48k; Arrestin) from the inner segments to the outer segments was analyzed using polyclonal and monoclonal antibodies. The concentrations of mRNA change about threefold for rhodopsin and about sixfold for S-Ag in cyclic, independent modes during the normal light-dark cycle. Kinetic analysis indicates that the oscillations of S-Ag mRNA levels are due to changes in the transcriptional activity of the gene itself. An experimental model is presented summarizing the relationships between mRNA levels, protein localization, disc shedding, and phototransduction in the photoreceptors cells.

Maintenance of opsin and S-antigen gene expression in RCS dystrophic rats following RPE transplantation

The effects of retinal pigment epithelium (RPE) transplantation in rescuing photoreceptor cells (PRC) were studied in RCS rats bearing the rdy mutation. RPE preparations from Long-Evans rats were transplanted into the subretinal space of post-natal (P) 17-19-day-old RCS rats. Age-matched RCS animals in the control group received injections of the transplantation vehicle buffer alone. The animals were killed at various post-natal ages after RPE transplantation. Immunocytochemical studies using antibodies to opsin and S-antigen indicated intact photoreceptor cells in the transplanted retinas. In contrast age-matched sham-injected animals did not show any rescue of photoreceptor cells at P90. Single RPE transplantation of 60,000 cells in each eye resulted in restoration of near normal mRNA levels for opsin, and S-antigen proteins. Comparisons of mRNA levels of two visual proteins using cDNA probes demonstrated a therapeutic effect of RPE transplantation in preventing a progressive decline in mRNA levels due to retinal degeneration. In contrast, P109 sham-injected controls showed no detectable mRNA levels for these proteins. In vitro protein synthesis in RPE-transplanted retinas implied further competence of these retinas. These data suggest that RPE transplantation not only rescues photoreceptors from degeneration, but more importantly, it allows normal transcription and translation in these cells rendering them capable of participating in the visual and signal transduction cascade.

Photoreceptors of the retina and pinealocytes of the pineal gland share common components of signal transduction

Light absorbed by retinal photoreceptors triggers a cascade of reactions that initiate cGMP hydrolysis, cation channel closure and membrane hyperpolarization. Down-regulation of the cascade involves additional proteins that interfere with amplification along the cascade. Pinealocytes are activated by norepinephrine during the dark phase of the day/night cycle. Mature pinealocytes of the mammalian pineal express the known photoreceptor proteins that are implicated in down-regulation of the visual cascade, but the cascade components that produce cGMP hydrolysis and membrane hyperpolarization are absent. Pinealocytes accumulate cyclic AMP minimally when norepinephrine activates their beta adrenergic receptors alone, but the response is potentiated by the simultaneous activation of their alpha-1 adrenergic receptors. A model is proposed whereby phosducin, a phosphoprotein that binds the beta,gamma subunit of G-proteins, could modulate the synthesis of cyclic AMP by buffering the amount of beta,gamma G-protein subunits that are available for activating adenylate cyclase.