MicroRNA-122 modulates the rhythmic expression profile of the circadian deadenylase Nocturnin in mouse liver.

Nocturnin is a circadian clock-regulated deadenylase thought to control mRNA expression post-transcriptionally through poly(A) tail removal. The expression of Nocturnin is robustly rhythmic in liver at both the mRNA and protein levels, and mice lacking Nocturnin are resistant to diet-induced obesity and hepatic steatosis. Here we report that Nocturnin expression is regulated by microRNA-122 (miR-122), a liver specific miRNA. We found that the 3'-untranslated region (3'-UTR) of Nocturnin mRNA harbors one putative recognition site for miR-122, and this site is conserved among mammals. Using a luciferase reporter construct with wild-type or mutant Nocturnin 3'-UTR sequence, we demonstrated that overexpression of miR-122 can down-regulate luciferase activity levels and that this effect is dependent on the presence of the putative miR-122 recognition site. Additionally, the use of an antisense oligonucleotide to knock down miR-122 in vivo resulted in significant up-regulation of both Nocturnin mRNA and protein expression in mouse liver during the night, resulting in Nocturnin rhythms with increased amplitude. Together, these data demonstrate that the normal rhythmic profile of Nocturnin expression in liver is shaped in part by miR-122. Previous studies have implicated Nocturnin and miR-122 as important post-transcriptional regulators of both lipid metabolism and circadian clock controlled gene expression in the liver. Therefore, the demonstration that miR-122 plays a role in regulating Nocturnin expression suggests that this may be an important intersection between hepatic metabolic and circadian control.

A comprehensive analysis of gene expression profiles in distal parts of the mouse renal tubule.

The distal parts of the renal tubule play a critical role in maintaining homeostasis of extracellular fluids. In this review, we present an in-depth analysis of microarray-based gene expression profiles available for microdissected mouse distal nephron segments, i.e., the distal convoluted tubule (DCT) and the connecting tubule (CNT), and for the cortical portion of the collecting duct (CCD; Zuber et al., Proc Natl Acad Sci USA 106:16523-16528, 2009). Classification of expressed transcripts in 14 major functional gene categories demonstrated that all principal proteins involved in maintaining the salt and water balance are represented by highly abundant transcripts. However, a significant number of transcripts belonging, for instance, to categories of G-protein-coupled receptors or serine/threonine kinases exhibit high expression levels but remain unassigned to a specific renal function. We also established a list of genes differentially expressed between the DCT/CNT and the CCD. This list is enriched by genes related to segment-specific transport functions and by transcription factors directing the development of the distal nephron or collecting ducts. Collectively, this in silico analysis provides comprehensive information about relative abundance and tissue specificity of the DCT/CNT and the CCD expressed transcripts and identifies new candidate genes for renal homeostasis.

Neurochemical profile of the mouse hypothalamus using in vivo 1H MRS at 14.1T.

The hypothalamus plays an essential role in the central nervous system of mammals by among others regulating glucose homeostasis, food intake, temperature, and to some extent blood pressure. Assessments of hypothalamic metabolism using, e.g. (1)H MRS in mouse models can provide important insights into its function. To date, direct in vivo (1)H MRS measurements of hypothalamus have not been reported. Here, we report that in vivo single voxel measurements of mouse hypothalamus are feasible using (1)H MRS at 14.1T. Localized (1)H MR spectra from hypothalamus were obtained unilaterally (2-2.2 microL, VOI) and bilaterally (4-4.4 microL) with a quality comparable to that of hippocampus (3-3.5 microL). Using LCModel, a neurochemical profile consisting of 21 metabolites was quantified for both hypothalamus and hippocampus with most of the Cramér-Rao lower bounds within 20%. Relative to the hippocampus, the hypothalamus was characterized by high gamma-aminobutryric acid and myo-inositol, and low taurine concentrations. When studying transgenic mice with no glucose transporter isoform 8 expressed, small metabolic changes were observed, yet glucose homeostasis was well maintained. We conclude that a specific neurochemical profile of mouse hypothalamus can be measured by (1)H MRS which will allow identifying and following metabolic alterations longitudinally in the hypothalamus of genetic modified models.

Dysfunction of epithelial sodium transport: from human to mouse.

The highly amiloride-sensitive epithelial sodium channel (ENaC) is an apical membrane constituent of cells of many salt-absorbing epithelia. In the kidney, the functional relevance of ENaC expression has been well established. ENaC mediates the aldosterone-dependent sodium reabsorption in the distal nephron and is involved in the regulation of blood pressure. Mutations in genes encoding ENaC subunits are causative for two human inherited diseases: Liddle's syndrome, a severe form of hypertension associated with ENaC hyperfunction, and pseudohypoaldosteronism (PHA-1), a salt-wasting syndrome caused by decreased ENaC function. Transgenic mouse technologies provide a useful tool to study the role of ENaC in vivo. Different mouse lines have been established in which each of the ENaC subunits was affected. The phenotypes observed in these mice demonstrated that each subunit is essential for survival and for regulation of sodium transport in kidney and colon. Moreover, the alpha subunit plays a specific role in the control of fluid absorption in the airways at birth. Such mice can now be used to study the role of ENaC in various organs and can serve as models to understand the pathophysiology of these human diseases.

Differential distribution of MAP1a and aldolase c in adult mouse cerebellum.

MAP1a is a microtubule-associated protein with an apparent molecular weight of 360 kDa that is found in the axonal and dendritic processes of neurons. Two monoclonal anti-MAP1a antibodies anti-A and anti-BW6, revealed different epitope distributions in the adult mouse cerebellum. Anti-A stained Purkinje and granule cells uniformly throughout the cerebellum. In contrast, anti-BW6 selectively stained the dendriites of a subset of Purkinje cells, revealing parasagittal bands of immunoreactivity in the molecular layer. The compartmentation of the BW6 epitope was compared to the Purkine cells as revealed by immunostaining with anti-zebrin II, a well known antigen expressed selectively by bands of Purkinje cells. The anti-BW6 staining pattern was complementary to the zebrin II bands, the zebrin II- Purkinjke cells having BW6+ dendrites. These results demonstrate that MAP1a is present in two forms in the mouse cerebellum, one of which is segregated into parasagittal bands. This may indicate a unique MAP1a isoform or may reflect differences in the metabolic states of Purkinje cell classes, and regional differences in their functions.

Binding of low concentration of peptide to H-2Kd produced in insect cells requires mouse beta 2-microglobulin co-expression.

A recombinant baculovirus expressing the murine class I MHC heavy chain H-2Kd cDNA under the transcriptional control of Autografa californica nuclear polyhedrosis virus (AcNPV) polyhedrin promoter has been isolated and used to infect Sf9 lepidopteran cells either alone or in association with a previously isolated virus expressing mouse beta 2-microglobulina (beta 2-ma). When infected with the heavy chain-encoding virus alone, H-2Kd was produced in a beta 2-m-free conformation detected on the surface of infected cells by conformation-independent antibodies. When Sf9 cells were co-infected with both viruses, approximately 10% of the heavy chain pool was engaged in the formation of native heterodimeric MHC class I molecules, which were glycosylated and transported to the cell surface as demonstrated by radio-binding experiments and flow cytometry. The assembly of the recombinant class I molecule was dependent on peptide, since heterodimer formation was brought about by H-2Kd-specific peptide ligands both in vivo, upon incubation with dually infected cells, and in vitro, in cell-free detergent extracts. In addition, a change in heavy chain conformation was brought about upon incubation with high concentrations (100 microM) of an H-2Kd-restricted octapeptide epitope from Plasmodium berghei. Furthermore, using low concentrations (3 nM) of a photoaffinity label derivative of this peptide, we show direct binding to cells co-expressing class I heavy chain and mouse beta 2-m but not to cells expressing free heavy chain only.

Antigen-secretory IgA immune complexes are retro-transported into mouse Peyer's patches: immunotargeting to dendritic cells

RÉSUMÉ Les plaques de Peyer (PP) représentent le site d'entrée majeur des pathogènes au niveau des muqueuses intestinales. Après avoir traversé la cellule M, l'antigène est pris en charge par les cellules dendritiques (DC) de la région sub-épithéliale du dôme des PP. Ces dernières activent une réponse immunitaire qui conduit à la production de l'IgA de sécrétion (SIgA), l'anticorps majeur au niveau muqueux. Des études précédentes dans notre laboratoire ont démontré qu'après administration de SIgA dans des anses intestinales de souris, les SIgA se lient spécifiquement aux cellules M, entrent dans les PP, et sont éventuellement internalisées par les DC. Le but de ce travail est de comprendre la relevance biologique de l'entrée des SIgA dans les PP et leur relevance physiologique dans l'homéostasie mucosale. Dans un premier temps, nous avons montré en utilisant une méthode de purification optimisée basée sur une isolation magnétique, que, en plus des DC myéloïdes (CD11c+/CD11b+) et des DC lymphoïdes (CD11c+/CD8+), les PP de souris contiennent un nouveau sous-type de DC exprimant les marqueurs CD11c et CD19. L'utilisation de la microscopie confocale nous a permis de démontrer que les DC myéloïdes internalisent des SIgA, contrairement aux DC lymphoïdes qui n'interagissent pas avec les SIgA, alors que le nouveau sous-type de DC exprimant CD19 lie les SIgA. En plus, nous avons démontré qu'aucune des DC de rate, de ganglion bronchique ou de ganglion inguinal interagit avec les SIgA. Dans le but d'explorer si les SIgA peuvent délivrer des antigènes aux DC des PP in vivo, nous avons administré des complexes immunitaires formés de Shigella flexneri complexées à des SIgA, dans des anses intestinales de souris. Nous avons observé une entrée dans les PP, suivie d'une migration vers les ganglions mésentériques drainants, contrairement aux Shigella flexneri seules, qui n'infectent pas la souris par la voie intestinale. Shigella flexneri délivrée par SIgA n'induit pas de destruction tissulaire au niveau de l'intestin. En plus de l'exclusion immunitaire, ces résultats suggèrent un nouveau rôle des SIgA, qui consiste à transporter des antigènes à l'intérieur des PP dans un contexte non-inflammatoire. RÉSUMÉ DESTINÉ À UN LARGE PUBLIC L'intestin a pour rôle principal d'absorber les nutriments digérés tout au long du tube digestif, et de les faire passer dans le compartiment intérieur sanguin. Du fait de son exposition chronique avec un monde extérieur constitué d'aliments et de bactéries, l'intestin est un endroit susceptible aux infections et a donc besoin d'empêcher l'entrée de microbes. Pour cela, l'intestin est tapissé de "casernes" appelées les plaques de Peyer, qui appartiennent à un système de défense appelé système immunitaire muqueux. Les plaques de Peyer sont composées de différents types de cellules, ayant pour rôle de contrôler l'entrée de microbes et de développer une réaction immunitaire lors d'infection. Cette réaction immunitaire contre les microbes (antigènes) débute par la prise en charge de l'antigène par des sentinelles, les cellules dendritiques. L'antigène est préparé de façon à être reconnu par d'autres cellules appelées lymphocytes T capables d'activer d'autres cellules, les lymphocytes B. La réaction immunitaire résulte dans la production par les lymphocytes B d'un anticorps spécifique appelé IgA de sécrétion (SIgA) au niveau de la lumière intestinale. De manière classique, le rôle de SIgA au niveau de la lumière intestinale consiste à enrober les microbes et donc exclure leur entrée dans le compartiment intérieur. Dans ce travail, nous avons découvert une nouvelle fonction des SIgA qui consiste à introduire des antigènes dans les plaques de Peyer, et de les diriger vers les cellules dendritiques. Sachant que les SIgA sont des anticorps qui ne déclenchent pas de réactions de défense violentes dites inflammatoires, l'entrée des antigènes via SIgA serait en faveur d'une défense intestinale maîtrisée sans qu'il y ait d'inflammation délétère. Ces résultats nous laissent supposer que l'entrée d'antigènes via SIgA pourrait conduire le système immunitaire muqueux à reconnaître ces antigènes de manière appropriée. Ce mécanisme pourrait expliquer les désordres immunitaires de types allergiques et maladies auto-immunitaires que l'on rencontre chez certaines personnes déficientes en IgA, chez qui cette lecture d'antigènes de manière correcte serait inadéquate. ABSTRACT Peyer's patches (PP) represent the primary site for uptake and presentation of ingested antigens in the intestine. Antigens are sampled by M cells, which pass them to underlying antigen-presenting cells including dendritic cells (DC). This leads to the induction of mucosal T cell response that is important for the production of secretory IgA (SIgA), the chief antibody at mucosal surfaces. Previous studies in the laboratory have shown that exogenous SIgA administrated into mouse intestinal loop binds specifically to M cells, enter into PP, and is eventually internalized by DC. The aim of this work is to understand the biological significance of the SIgA uptake by PP DC and its physiological relevance for mucosal homeostasis. As a first step, we have shown by using an optimized MACS method that, in addition to the CD11c+/CD11b+ (myeloid DC) and CD11c+/CD8+ (lymphoid DC) subtypes, mouse PP contain a novel DC subtype exhibiting both CD11c and CD19 markers. By using a combination of MACS isolation and confocal microscopy, we have demonstrated that in contrast to the lymphoid DC which do not interact with SIgA, the myeloid DC internalize SIgA, while the CD19+ subtype binds SIgA on its surface. Neither spleen DC, nor bronchial-lymph node DC, nor inguinal lymph node DC exhibit such a binding specificity. To test whether SIgA could deliver antigens to PP DC in vivo, we administered SIgA-Shigella flexneri immune complexes into mouse intestinal loop containing a PP. We found that (i) SIgA-Shigella flexneri immune complexes enter the PP and are internalized by sub-epithelial dome PP DC, in contrast to Shigella flexneri alone that does not penetrate the intestinal epithelia in mice, (ii) immune complexes migrate to the draining mesenteric lymph node, (iii) Shigella flexneri carried via SIgA do not induce intestinal tissue destruction. Our results suggest that in addition to immune exclusion, SIgA transports antigens back to the PP under non-inflammatory conditions.

Comparative gene prediction in human and mouse

The completion of the sequencing of the mouse genome promises to help predict human genes with greater accuracy. While current ab initio gene prediction programs are remarkably sensitive (i.e., they predict at least a fragment of most genes), their specificity is often low, predicting a large number of false-positive genes in the human genome. Sequence conservation at the protein level with the mouse genome can help eliminate some of those false positives. Here we describe SGP2, a gene prediction program that combines ab initio gene prediction with TBLASTX searches between two genome sequences to provide both sensitive and specific gene predictions. The accuracy of SGP2 when used to predict genes by comparing the human and mouse genomes is assessed on a number of data sets, including single-gene data sets, the highly curated human chromosome 22 predictions, and entire genome predictions from ENSEMBL. Results indicate that SGP2 outperforms purely ab initio gene prediction methods. Results also indicate that SGP2 works about as well with 3x shotgun data as it does with fully assembled genomes. SGP2 provides a high enough specificity that its predictions can be experimentally verified at a reasonable cost. SGP2 was used to generate a complete set of gene predictions on both the human and mouse by comparing the genomes of these two species. Our results suggest that another few thousand human and mouse genes currently not in ENSEMBL are worth verifying experimentally.

Hypothalamus transcriptome profile suggests an anorexia-cachexia syndrome in the anx/anx mouse model

The anx/anx mouse displays poor appetite and lean appearance and is considered a good model for the study of anorexia nervosa. To identify new genes involved in feeding behavior and body weight regulation we performed an expression profiling in the hypothalamus of the anx/anx mice. Using commercial microarrays we detected 156 differentially expressed genes and validated 92 of those using TaqMan low-density arrays. The expression of a set of 87 candidate genes selected based on literature evidences was also quantified by TaqMan low-density arrays. Our results showed enrichment in deregulated genes involved in cell death, cell morphology and cancer as well as an alteration of several signaling circuits involved in energy balance including neuropeptide Y and melanocortin signaling. The expression profile along with the phenotype led us to conclude that anx/anx mice resemble the anorexia-cachexia syndrome typically observed in cancer, infection with human immunodeficiency virus or chronic diseases, rather than starvation, and that anx/anx mice could be considered a good model for the treatment and investigation of this condition.

Generation of mouse-induced pluripotent stem cells by transient expression of a single nonviral polycistronic vector

Induced pluripotent stem (iPS) cells have generated keen interestdue to their potential use in regenerative medicine. They havebeen obtained from various cell types of both mice and humans byexogenous delivery of different combinations of Oct4, Sox2, Klf4,c-Myc, Nanog, and Lin28. The delivery of these transcription factorshas mostly entailed the use of integrating viral vectors (retrovirusesor lentiviruses), carrying the risk of both insertional mutagenesisand oncogenesis due to misexpression of these exogenousfactors. Therefore, obtaining iPS cells that do not carry integratedtransgene sequences is an important prerequisite for their eventualtherapeutic use. Here we report the generation of iPS cell linesfrom mouse embryonic fibroblasts with no evidence of integrationof the reprogramming vector in their genome, achieved by nucleofectionof a polycistronic construct coexpressing Oct4, Sox2, Klf4,and c-Myc

Use of a short hPDE6b promoter for rod gene transfer in a model of severe retinal cystrophy, the Rd10 mouse

Purpose: Gene therapy of severe retinal dystrophies directly affecting photoreceptor is still a challenge in terms of clinical application. One of the main hurdles is to generate high transgene expression specifically in rods or cones. In the present study, we are investigating the possibility to drive hPDE6b expression in the Rd10 mouse retina using a specific sequence of the human PDE6b promoter. Methods: Two 5' flanking fragments of the human PDE6b gene: (-93 to +53 (146 bp) and -297 to +53 (350 bp, see Di Polo and Farber, 1995) were cloned in different plasmids in order to check their expression in vitro and in vivo. These elements drove the activity of either luciferase (pGL3 plasmids) or EGFP (AAV2/8 backbone). Then, an AAV2/8 vector carrying the PDE6b cDNA was tested with subretinal injections at P9 in the Rd10 eyes. Eye fundus, OCT, ERG recordings and histological investigations were performed to assess the efficacy of the gene transfer. Results: The short PDE6b promoter containing 146bp (-93 to +53) showed the highest activity in the Y-79 cells, as described previously (Di Polo and Farber, 1995). Subretinal administrations of AAV2/8-PDE6bpromoter-EGFP allowed a rapid expression specifically in rods and not in cones. The expression is faster than a vector containing the CMV promoter. The AAV2/8-PDE6bpromoter-PDE6b and the control vector were injected at P9 in the Rd10 mouse retina and investigated 5 weeks post-injection. Out of 14 eyes, 6 presented an increased rod sensitivity of about 300 fold, and increased a- and b-wave responses in ERG recordings. Flicker stimulations revealed that cones are also functional. OCT images and histological analyses revealed an increased ONL size in the injected area. The retina treated with the therapeutic vector presented 4-6 rows of photoreceptors with outersegments containing PDE6b. In the control eyes, only 2-4 rows of photoreceptors with almost no OS were observed . Conclusions: The 146 bp promoter sequence (-93 to + 53) is the shortest regulatory element described to date which allows to obtain efficient rod-specific expression in the context of somatic gene transfer. This first result is of great interest for AAV vector design in general allowing more space for the accommodation of transgenes of interest and good expression in rods. Moreover we showed the proof of principle of the efficacy of AAV2/8-PDE6bp-PDE6b vector in the Rd10 mouse model of severe photoreceptor degeneration without using neither AAV mutated capsids, nor self-complementary vectors.

Lack of antitumour activity of human recombinant tumour necrosis factor-alpha, alone or in combination with melphalan in a nude mouse human melanoma xenograft system.

The most promising developments in the field of isolated limb perfusion have centred around the use of the recombinant cytokine tumour necrosis factor-alpha (rTNF-alpha) in combination with melphalan. While the results of clinical trials are impressive, the exact antitumour mechanisms of rTNF-alpha and its role in combination with melphalan remain unclear. Our aim was to study the antitumour activity of human rTNF-alpha with or without the combination of melphalan in a nude mouse human melanoma xenograft system. In a first attempt to define the maximal tolerated single dose of rTNF-alpha in this setting, 15 animals were exposed to increasing doses of rTNF-alpha (60-2500 microg/kg intraperitoneally). All but one animal survived and tumour growth was not influenced by these single dose applications of rTNF-alpha even at the very high doses. Anti-tumour activity of repeated application of melphalan (three times 9 mg/kg in group 2 and three times 6 mg/kg in group 3), of rTNF-alpha alone (nine doses of 50 microg/kg in group 4), and of rTNF-alpha in combination with melphalan (nine doses of 50 microg/kg rTNF-alpha and three times 6 mg/kg melphalan in group 5) was further compared with non-treated animals (group 1). Tumour growth was significantly inhibited in all animals treated with melphalan (group 2, 3 and 5), but was not decreased in animals treated with rTNF-alpha alone (group 4). Mean final tumour volumes and mean tumour weight were not different in group 2 (789 +/- 836 mm3, 0.38 +/- 0.20 g), group 3 (1173 +/- 591 mm3, 0.55 +/- 0.29 g) and group 5 (230 +/- 632 mm3, 0.37 +/- 0.29 g), but significant lower than group 1 (3156 +/- 1512 mm3, 2.35 +/- 0.90 g) and group 4 (3228 +/- 1990 mm3, 2.00 +/- 1.16 g). There were no significant differences between high and low dose melphalan treatment and between melphalan treatment in combination with rTNF-alpha. Histological examination did not show differences between treated and non-treated animals besides slightly inhibited mitotic activities of tumour cells in melphalan-treated animals. While tumour growth of human xenotransplanted melanoma in nude mice could be inhibited by melphalan, we failed to demonstrate any antitumour effect of rTNF-alpha. The combination of melphalan and rTNF-alpha did not enhance the antiproliferative effect of melphalan alone. Human xenotransplanted tumours on nude mice might not be the ideal experimental setting for studies of potential direct antineoplastic activity of rTNF-alpha, and these results support the concept that TNF-alpha exerts its antitumour activity indirectly, possibly by impairing the tumour vasculature and by activating the immune system.

Vasopressin-dependent coupling between sodium transport and water flow in a mouse cortical collecting duct cell line.

Water balance is achieved through the ability of the kidney to control water reabsorption in the connecting tubule and the collecting duct. In a mouse cortical collecting duct cell line (mCCD(c11)), physiological concentrations of arginine vasopressin increased both electrogenic, amiloride-sensitive, epithelial sodium channel (ENaC)-mediated sodium transport measured by the short-circuit current (Isc) method and water flow (Jv apical to basal) measured by gravimetry with similar activation coefficient K(1/2) (6 and 12 pM, respectively). Jv increased linearly according to the osmotic gradient across the monolayer. A small but highly significant Jv was also measured under isoosmotic conditions. To test the coupling between sodium reabsorption and water flow, mCCD(c11) cells were treated for 24 h under isoosmotic condition with either diluent, amiloride, vasopressin or vasopressin and amiloride. Isc, Jv, and net chemical sodium fluxes were measured across the same monolayers. Around 30% of baseline and 50% of vasopressin-induced water flow is coupled to an amiloride-sensitive, ENaC-mediated, electrogenic sodium transport, whereas the remaining flow is coupled to an amiloride-insensitive, nonelectrogenic sodium transport mediated by an unknown electroneutral transporter. The mCCD(c11) cell line is a first example of a mammalian tight epithelium allowing quantitative study of the coupling between sodium and water transport. Our data are consistent with the 'near isoosmotic' fluid transport model.

Sleep deprivation effects on circadian clock gene expression in the cerebral cortex parallel electroencephalographic differences among mouse strains.

Sleep deprivation (SD) results in increased electroencephalographic (EEG) delta power during subsequent non-rapid eye movement sleep (NREMS) and is associated with changes in the expression of circadian clock-related genes in the cerebral cortex. The increase of NREMS delta power as a function of previous wake duration varies among inbred mouse strains. We sought to determine whether SD-dependent changes in circadian clock gene expression parallel this strain difference described previously at the EEG level. The effects of enforced wakefulness of incremental durations of up to 6 h on the expression of circadian clock genes (bmal1, clock, cry1, cry2, csnk1epsilon, npas2, per1, and per2) were assessed in AKR/J, C57BL/6J, and DBA/2J mice, three strains that exhibit distinct EEG responses to SD. Cortical expression of clock genes subsequent to SD was proportional to the increase in delta power that occurs in inbred strains: the strain that exhibits the most robust EEG response to SD (AKR/J) exhibited dramatic increases in expression of bmal1, clock, cry2, csnkIepsilon, and npas2, whereas the strain with the least robust response to SD (DBA/2) exhibited either no change or a decrease in expression of these genes and cry1. The effect of SD on circadian clock gene expression was maintained in mice in which both of the cryptochrome genes were genetically inactivated. cry1 and cry2 appear to be redundant in sleep regulation as elimination of either of these genes did not result in a significant deficit in sleep homeostasis. These data demonstrate transcriptional regulatory correlates to previously described strain differences at the EEG level and raise the possibility that genetic differences underlying circadian clock gene expression may drive the EEG differences among these strains.