Induction of c-fos protein-like immunoreactivity in the rat and hamster pineal gland after the onset of darkness

Expression and regulation of Icer mRNA in the Syrian hamster pineal gland

Inducible-cAMP early repressor (ICER) is a potent inhibitor of CRE (cAMP-related element)-driven gene transcription. In the rat pineal gland, it has been proposed to be part of the mechanisms involved in the shutting down of the transcription of the gene coding for arylalkylamine N-acetyltransferase (AA-NAT, the melatonin rhythm-generating enzyme). In this study, we report that ICER is expressed in the pineal gland of the photoperiodic rodent Syrian hamster although with some difference compared to the rat. In the Syrian hamster pineal, Icer mRNA levels, low at daytime, displayed a 20-fold increase during the night. Nighttime administration of a beta-adrenergic antagonist, propranolol, significantly reduced Icer mRNA levels although daytime administration of a beta-adrenergic agonist, isoproterenol, was unable to raise the low amount of Icer mRNA. These observations indicate that Icer mRNA expression is induced by the clock-driven norepinephrine release and further suggest that this stimulation is restricted to nighttime, as already observed for Aa-nat gene transcription. Furthermore, we found that the daily profile of Icer mRNA displayed photoperiodic variation with a lengthening of the nocturnal peak in short versus long photoperiod. These data indicate that ICER may be involved in both daily and seasonal regulation of melatonin synthesis in the Syrian hamster.

Trans-synaptic control of NGFI-A and jun-B expression: contrasting transcriptional and post-transcriptional mechanisms directed by common receptors

Previous studies have demonstrated that of the multiple primary response gene products which are induced in the rat pineal gland through a nocturnally activated adrenoceptor-linked mechanism. JunB is the principal component of a dark phase-specific activator protein-1 DNA binding complex. JunB is therefore implicated as a nuclear component of the mechanisms that determine nocturnal changes in pineal function. It is now shown that the marked increase in jun-B mRNA expression following norepinephrine stimulation in vitro, is mediated through a post-transcriptional mechanism that involves mRNA stabilization. This mode of regulation is contrasted with that controlling the expression of other primary response genes. In the case of NGFI-A, a co-regulated primary response gene which is controlled through a pharmacologically similar pathway, nuclear run-on transcription assays have shown that pineal mRNA levels are elevated through an increase in transcription rate that can be measured both in vitro and in vivo. These results show that multiple molecular mechanisms are engaged to effect the genomic consequences of adrenoceptor stimulation, and that rhythmic changes in gene expression may be controlled by post-transcriptional mechanisms involving mRNA stability.

Circadian expression of transcription factor Fra-2 in the rat pineal gland

Physiological changes in Fos-like immunoreactivity in the rat pineal gland are shown here to be due primarily to changes in a 42/46-kDa Fos-related antigen (Fra). Studies are presented that indicate this 42/46-kDa Fra is Fra-2, a poorly understood member of the Fos family of transcription factors. Both Fra-2 mRNA and protein are absent during the day and increase robustly at night on a circadian basis; organ culture studies indicate that regulation is mediated by an adrenergic-->cyclic AMP mechanism. AP-1 binding activity changes in parallel to changes in the level of Fra-2 protein.

A daily rhythm of activator protein-1 activity in the rat pineal is dependent upon trans-synaptic induction of JunB

The daily cycle of phenotypic variation in the mammalian pineal provides a unique model for the investigation of the molecular mechanisms that regulate neurotransmitter synthesis. In the rat, a circadian adrenergic mechanism directs a change in serotonin metabolism that results in the nocturnal production of melatonin. Activity of the activator protein-1 transcriptional regulatory complex, as demonstrated by band-shift assays of rat pineal gland extracts, has now been shown to exhibit a rhythm, in vivo, which is temporally correlated with the rhythm of melatonin synthesis. Thus, nocturnal activator protein-1 activity (23.00 h) is markedly elevated, being 8-fold higher than the level of light-phase activity (P < 0.005). The nocturnal activator protein-1 protein complex is induced through a trans-synaptic, beta-adrenoceptor-linked mechanism and is characterized by the prolonged participation of JunB as demonstrated using antibodies for specific activator protein-1 proteins. Indeed, JunB appears to be a major component of nocturnal changes in activator protein-1 activity, JunD forming an additional, constitutive component which is not affected by the nocturnal adrenergic signal. The alpha 1-adrenoreceptor-linked c-Fos protein, which is coordinately induced with JunB, does not form a stable component of nocturnal activator protein-1 activity. In contrast, parallel experiments showed that c-Fos does form a major component of the hippocampal activator protein-1 complex that is induced in rats following kainic acid treatment. In the pineal, a similar, although not identical, pattern of activator protein-1 activation has also been demonstrated in cultured glands following treatment with norepinephrine. Immunoblotting has demonstrated parallel accumulation of JunB and c-Fos protein in pineal nuclear fractions following stimulation both in vivo and in vitro. The results provide evidence of posttranscriptional selection of neurotransmitter-stimulated activator protein-1 protein complexes, a mechanism which complements the differential induction of fos and jun genes in the pineal, and serves to generate a specific activator protein-1 transcription factor complex. This finding has general implications for the functional interpretation of fos and jun gene induction in neuronal systems. The stable JunB complex demonstrated here may be considered as one component of a timing mechanism which acts to perpetuate synaptic signals and thereby maintain an appropriate period of nocturnal pineal function.

Expression of c-fos in the rat cerebral cortex after focal ischemia and reperfusion

Time-dependent changes in c-fos-like immunoreactivity (c-fos-LI) were studied in the rat during focal cerebral ischemia and reperfusion after middle cerebral artery (MCA) occlusion. In the permanent ischemia model, the levels of c-fos-LI increased for the first 30 min of ischemia in neuronal nuclei in the lesioned hemisphere. They reached a maximum at 60 min. The level in the parietal cortex (PC) diminished considerably after 120 min, and in the cingulate cortex (CC) it gradually decreased to near the control value at 180 min. Regional cerebral blood flow (rCBF) in the PC fell to 32% and that in the CC fell to 64% of pre-ischemic values after MCA occlusion. Reperfusion induced strong expression of c-fos-LI in the PC and CC after 6 h of reperfusion that followed 30 min of ischemia. The c-fos-LI was effectively reduced by preadministration of the N-methyl-D-aspartate (NMDA) receptor antagonist, ketamine (100 mg/kg, IP). These findings suggest that the expression of c-fos after ischemia may be immediately activated through NMDA receptors and may spread to surrounding regions in a manner sensitive to reductions in rCBF. Reperfusion after ischemia also appears to cause activation of expression of c-fos and of intracellular signal transduction.

Noradrenergic regulation of c-jun expression in the rat pineal gland in culture: positive and negative components

One component of the nocturnal changes in cellular immediate-early gene expression in the rat pineal gland is a decrease in c-jun expression, mediated through beta-adrenoceptors. An in vitro study of the intracellular mechanisms which control c-jun expression has now shown that a norepinephrine-induced increase in c-jun mRNA levels in organ-cultured pineals is differentially modulated by protein kinase inhibitors; N-(2-guanidinoethyl)-5-isoquinolinesulfonamide (HA-1004) potentiated the response; however, in the presence of 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7), a significant decrease in c-jun mRNA was found. Treatment with HA-1004 alone elevated the level of c-jun mRNA, H-7 alone was without effect. Forskolin together with 3-isobutyl-1-methylxanthine suppressed c-jun, whereas phorbol 12,13-dibutyrate raised c-jun mRNA levels. The results demonstrate opposing pathways for c-jun regulation in the pineal gland, and indicate that the nocturnal attenuation of c-jun expression involves selective activation of a negative pathway which may be linked to cAMP.

Differential intracellular mechanisms mediate the co-ordinate induction of c-fos and jun-B in the rat pineal gland

In the rat pineal gland the immediate early genes c-fos and jun-B are co-ordinately induced in vivo following the onset of darkness, and in vitro following treatment with adrenergic drugs. An extensive in vitro analysis of the mechanisms which regulate the induction of these two genes has revealed that, although there are common pathways of control, c-fos and jun-B exhibit differential regulation by adrenoceptor types, second messenger pathways and protein kinase C. The presence of differential intracellular mechanisms of regulation provides precise control over the expression pattern of immediate early genes, a pattern which is crucial for cellular response since the combinatorial actions of the products of these genes are a determinant of target gene activation. The pineal gland is a unique experimental model in which the molecular pharmacology of immediate early gene regulation can be investigated.

Neurotransmitter-stimulated immediate-early gene responses are organized through differential post-synaptic receptor mechanisms

The products of the cellular immediate-early genes (IEGs) are thought to act as messengers in the coupling of trans-synaptic stimuli with altered neuronal gene expression. However, the manner in which neurotransmission specifies particular responses through the IEGs is undefined. In this report, mRNA and transcription analysis of a precisely-timed, physiological IEG response illustrates how an IEG signal may be organized through differential neurotransmitter receptor activation. The nocturnal pattern of IEG expression in the rat pineal gland has been shown to be differentially regulated through post-synaptic adrenergic receptors. Induction of the c-fos gene is primarily mediated through alpha 1-receptors, whereas the coordinately regulated jun-B gene exhibits dual regulation through alpha 1- and beta-receptors. A simultaneous repression of c-jun expression is partly mediated through a beta-receptor mechanism. In vitro analysis of IEGs in cultured pineal glands has confirmed the receptor-specific link between adrenergic neurotransmission and IEG induction. The pineal is a unique neuroendocrine model in which the characteristics and function of the IEG third messenger system may be defined.

In situ hybridization analysis of c-fos and c-jun expression in the rat brain following transient forebrain ischemia

Early induction of the mRNAs encoding the c-Fos and c-Jun nuclear proteins was examined in rat brain by in situ hybridization at various timepoints following global forebrain ischemia by the method of four-vessel occlusion. All animals were subjected to 20 min of transient ischemia. This produced a pattern of proto-oncogene activation that was most intense in the granule cells of the dentate gyrus 30 min after ischemia, while the hilar cells in the dentate and the pyramidal cells of the CA3 region in the hippocampus showed a more delayed but robust expression of these immediate early genes at 1 h. The neurons of the CA1 region exhibited a more moderate hybridization signal at 1-2 h postischemia. Very little hybridization signal for either immediate early gene could be detected in animals perfused with fixative immediately following ischemia, suggesting that cellular energy levels may have to be restored to a certain level before efficient de novo mRNA synthesis can occur. In the cerebellum, a similar temporal pattern was observed: the granule cells exhibited a prompt but patchy expression of c-fos and c-jun that was followed by a delayed signal in the Purkinje cells. Without exception c-fos and c-jun appeared to be expressed in unison, although the time course of c-fos and c-jun mRNA accumulation and decay was different in various brain regions: invariably the cerebellum returned rapidly to its baseline with virtually no remaining signal at 3 h postischemia, while c-fos and c-jun activation in the hippocampus remained high at 3 h and returned to baseline by 6 h. Several other brain regions showed early production of c-fos and c-jun mRNAs, such as the medial habenula, piriform cortex, the amygdala, the centromedian, lateral posterior, paracentral, intermediodorsal and reuniens nuclei of the thalamus and the ventromedial and dorsal nuclei of the hypothalamus; in the brainstem, the trapezoid body and the noradrenergic neurons of the locus ceruleus as well as the adrenergic neurons in the ventrolateral medulla (C1 group) and nucleus tractus solitarius (C2 group) regions displayed slightly less intense hybridization signals. In addition, the ependyma of the lateral ventricles and the third ventricle showed a prompt albeit short-lived production of c-fos and c-jun mRNAs. Sham-operated animals as well as animals that had survived to one week postischemia showed either no or only trace levels of hybridization signal.(ABSTRACT TRUNCATED AT 400 WORDS)

Fos-like immunoreactivity in cultured rat pinealocytes

The expression of Fos-like proteins in cultured rat pinealocytes was investigated immunocytochemically. Pineal glands of 2-day-old rats were dissociated and maintained in culture for 13 days, the last 24 h deprived of animal sera. The pinealocytes were identified morphologically and by serotonin-immunostaining. Incubations with phorbol dibutyrate (PDBu), 8-bromo-cAMP and isoprenaline were carried out for 2 h to test whether Fos-like protein synthesis is activated via serum response element (SRE), calcium/cyclic AMP response element (Ca/CRE) and beta-receptors, respectively. In untreated serum-deprived control cultures, one third of pinealocytes were Fos-immunoreactive suggesting that Fos protein may have a homeostatic role. In cultures incubated with PDBu, more than 70% of the pinealocytes had Fos-like immunoreactive material in their nuclei. Similarly, in cultures incubated with 8-bromo-cAMP or isoprenaline, more than 70% of the pinealocytes were Fos positive. The c-fos gene could be involved in the regulation of pineal melatonin synthesis and SRE and Ca/CRE probably participate in its activation process in pinealocytes.