NM A22834 (Albrecht) 3 Across a spectrum of living organisms, ranging from cyanobacteria to humans, it has been observed that biological functions follow a pattern of circadian rhythmicity.These endogenous rhythms display a periodicity close to 24 hours in the absence of environmental cues, thus reflecting the existence of an intrinsic biological clock. In mammals, circadian rhythms in different tissues are coordinated by a master clock located in the suprachiasmatic nucleus (SCN) of the anterior hypothalamus 1 . This circadian clock is thought to be advantageous in synchronising physiological and biochemical pathways, allowing the organism to anticipate daily changes, thus ensuring better adaptation to the environment 2 .The oscillatory mechanism of the circadian clock has been unraveled by means of genetic analysis in Drosophila and mammals [3][4][5] . In the latter, the heterodimeric complex of two transcriptional activators, CLOCK and BMAL1 (MOP3), induce the expression of several genes by interacting with the enhancer elements, termed E-boxes, of their promoters. Amongst these genes are Per1, Per2, Cry1 and Cry2, whose protein products, upon entering the nucleus, inhibit the activity of the CLOCK/BMAL1 complex, and thereby generating an inhibitory feedback loop driving recurrent rhythms in mRNA and protein levels of their own genes. This molecular mechanism seems to be present in the local clocks of most tissues and brain regions. Furthermore, these different clocks may then be synchronized by the SCN via neural and endocrine outputs 6 . Transporter 1, also known as Glast) is found to be reduced in these mice. Excess glutamate is cleared from the synaptic cleft by glutamate transporters 10 , located on astroglial cells and transported back to the neuron via the glutamine-glutamate cycle.A deficit in the removal of glutamate from the synaptic cleft, results in a hyperglutamatergic state and is suggested to produce alterations at the behavioral level 10,11 .Importantly, a hyper-glutamatergic state has been implicated in the aetiology of alcohol dependence [12][13][14] . We observe that in Per2 Brdm1 mutant mice voluntary alcohol consumption is enhanced. In humans we find an association between alcoholic patients and genetic variations in the human PER2 gene. Acamprosate, a medication thought to dampen a hyper-glutamatergic state in the alcohol dependent human brain 15-17 reduces augmented glutamate levels and normalizes enhanced alcohol consumption in Per2 Brdm1 mutant mice. These findings support the view that a hyperglutamatergic state can be involved in several aspects of alcohol dependence [12][13][14][18][19][20] . RESULTS Glutamate transporters in Per2 Brdm1 miceWild type and Per2 Brdm1 mutant mice differ in their behavioral response to a light pulse administered at zeitgeber time (ZT) 14 9 (ZT0 corresponds to lights on and ZT12 to lights off). Therefore, we set out to search for a difference in gene expression between wild type and Per2 Brdm1 mutant mice at ZT15. This time point has been chosen beca...

The transcription factor activator protein 1 (AP-1) 1 was one of the first mammalian transcription factors to be identified, but its physiological functions are still being unraveled. AP-1 is involved in cellular proliferation, transformation, survival, cell death, and the immune response (1, 2). AP-1 converts extracellular signals into changes of the expression of target genes, and AP-1 binding sites are found in a large number of genes. AP-1 is not a single protein, but a homo-or heterodimer composed of members of the JUN, FOS, ATF, and other protein families (1, 2). With the exception of cell cycle regulatory genes, because of the structural and regulatory complexity of AP-1, the knowledge of AP-1 target genes mediating AP-1 functions is far from complete (1, 2). c-JUN is one of the best characterized components of AP-1 (3). Genetic evidence suggests that c-JUN is essential for development and proliferation (1-3). Activity of c-JUN is controlled at multiple levels, first by changes in gene transcription, mRNA turnover, and protein stability, second by interaction with other transcription factors, and third by phosphorylation of its NH 2 -terminal transactivation domain (1-6).The phosphorylation sites required for inducible c-JUN activation have been mapped to serines 63 and 67. A family of 10 highly homologous serine/threonine protein kinases derived from three genes by alternative splicing has been identified that specifically phosphorylate these residues in c-JUN and has therefore been named c-JUN NH 2 -terminal protein kinases (JNK) 1-3 (7, 8). So far, no other protein kinases have been identified that phosphorylate the NH 2 terminus of c-JUN (6, 7). Importantly, early work demonstrated that JNK not only phosphorylate c-JUN, but also bind to a region called the ␦ domain, which is located immediately NH 2 -terminal of the c-JUN transactivation domain (6 -10). Binding of JNK to c-JUN is a remarkable example of a high affinity signaling complex (6 -10). Further studies of the complex in intact cells showed that it does not require the JNK catalytic activity or the presence of the phospho-acceptor sites in c-JUN (11). Presumably, the c-JUN-JNK interaction serves two purposes, first it provides the specificity of JNK for c-JUN, and second it helps to increase the local concentration of JNK at gene promoters that bind c-JUN, thereby enhancing c-JUN-mediated transcription (4).Like the c-JUN protein, JNK have been implicated in numerous biological roles in response to growth factors, stress, and inflammatory cytokines, implying that JNK may mediate their gene regulatory effects mainly through c-JUN (12-14). However, for several reasons this is unlikely. First, JNK phosphorylate other transcription factor substrates, such as ATF-2 (15) and ELK-1 (16); second, individual JNK isoforms display different affinities for c-JUN in vitro (8, 9); and third, the phenotypes of c-JUN and JNK knockout mice show no obvious overlapping phenotype (13,17,18). Therefore, one of the most intriguing questions regarding the c-JUN-JNK i...

SummaryChlamydia pneumoniae causes respiratory infections. In chronic diseases associated with Chlamydia , such as arteriosclerosis, C. pneumoniae is present in a persistent form, which might participate in pathogenesis of chronic inflammatory disease. To elucidate how these intracellular bacteria modulate host-cells during persistence, we compared the expression pattern of a range of host genes after short (24 h) and long (up to 7 days) times of chlamydia infection in HeLa-cells. One day post infection, in three cellculture models of persistence, namely treatment with penicillin or IFN-g g g g , or iron-depletion, infection induced the genes of CTGF, IL-6, IL-8, IL-11, LIF, EGR-1 and ETV4 in a similar fashion. However, after a longer time, two modes of host-cell reaction emerged that were dependent on the persistence model used. After IFN-g g g g and penicillin treatment chlamydia-induced host-cell gene expression was inhibited, while it stayed upregulated in iron-depletion. Human monocytes/macrophages, in which persistence naturally occurs, were additionally investigated: for several genes, UV-inactivated and viable chlamydia caused long-lasting upregulation. Thus, this study reveals (i) the ability of C. pneumoniae to participate in two putative pathomechanisms of persistence, silencing and permanent activation, which might represent different in vivo situations and (ii) a strong dependence on the mode of persistence induction.

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The periodic succession of night and day has influenced life on earth for millions of years. Many organisms have "internalized" this periodic change in the form of the circadian clock. Its main function is to organize the time course of biochemical, physiological and behavioural processes thereby optimizing an organism's performance in anticipating changing environmental conditions. Therefore, it is important to understand the underlying mechanisms that connect the core pacemaker, which is located in the suprachiasmatic nuclei (SCN) of the hypothalamus, with peripheral organs. Several laboratories set out to identify genes that are under the influence of the circadian clock. It appears that the circadian clock coordinates transcription of key metabolic pathways thereby orchestrating the time course of physiological and behavioural processes. We review these investigations and put our experiments, the comparison of gene expression in SCN tissue of Per2 mutant and wild-type mice, in the context of these findings.