Social insect genomes exhibit dramatic evolution in gene composition and regulation while preserving regulatory features linked to sociality.

Genomes of eusocial insects code for dramatic examples of phenotypic plasticity and social organization. We compared the genomes of seven ants, the honeybee, and various solitary insects to examine whether eusocial lineages share distinct features of genomic organization. Each ant lineage contains ∼4000 novel genes, but only 64 of these genes are conserved among all seven ants. Many gene families have been expanded in ants, notably those involved in chemical communication (e.g., desaturases and odorant receptors). Alignment of the ant genomes revealed reduced purifying selection compared with Drosophila without significantly reduced synteny. Correspondingly, ant genomes exhibit dramatic divergence of noncoding regulatory elements; however, extant conserved regions are enriched for novel noncoding RNAs and transcription factor-binding sites. Comparison of orthologous gene promoters between eusocial and solitary species revealed significant regulatory evolution in both cis (e.g., Creb) and trans (e.g., fork head) for nearly 2000 genes, many of which exhibit phenotypic plasticity. Our results emphasize that genomic changes can occur remarkably fast in ants, because two recently diverged leaf-cutter ant species exhibit faster accumulation of species-specific genes and greater divergence in regulatory elements compared with other ants or Drosophila. Thus, while the "socio-genomes" of ants and the honeybee are broadly characterized by a pervasive pattern of divergence in gene composition and regulation, they preserve lineage-specific regulatory features linked to eusociality. We propose that changes in gene regulation played a key role in the origins of insect eusociality, whereas changes in gene composition were more relevant for lineage-specific eusocial adaptations.

A non-circadian role for clock-genes in sleep homeostasis: a strain comparison.

BACKGROUND: We have previously reported that the expression of circadian clock-genes increases in the cerebral cortex after sleep deprivation (SD) and that the sleep rebound following SD is attenuated in mice deficient for one or more clock-genes. We hypothesized that besides generating circadian rhythms, clock-genes also play a role in the homeostatic regulation of sleep. Here we follow the time course of the forebrain changes in the expression of the clock-genes period (per)-1, per2, and of the clock-controlled gene albumin D-binding protein (dbp) during a 6 h SD and subsequent recovery sleep in three inbred strains of mice for which the homeostatic sleep rebound following SD differs. We reasoned that if clock genes are functionally implicated in sleep homeostasis then the SD-induced changes in gene expression should vary according to the genotypic differences in the sleep rebound. RESULTS: In all three strains per expression was increased when animals were kept awake but the rate of increase during the SD as well as the relative increase in per after 6 h SD were highest in the strain for which the sleep rebound was smallest; i.e., DBA/2J (D2). Moreover, whereas in the other two strains per1 and per2 reverted to control levels with recovery sleep, per2 expression specifically, remained elevated in D2 mice. dbp expression increased during the light period both during baseline and during SD although levels were reduced during the latter condition compared to baseline. In contrast to per2, dbp expression reverted to control levels with recovery sleep in D2 only, whereas in the two other strains expression remained decreased. CONCLUSION: These findings support and extend our previous findings that clock genes in the forebrain are implicated in the homeostatic regulation of sleep and suggest that sustained, high levels of per2 expression may negatively impact recovery sleep.

The cuticle : not only a barrier for plant defence: A novel defence syndrome in plants with cuticular defects.

The cuticle is a physical barrier that prevents water loss and protects against irradiation, xenobiotics and pathogens. This classic textbook statement has recently been revisited and several observations were made showing that this dogma falls short of being universally true. Both transgenic Arabidopsis thaliana lines expressing cell wall-targeted fungal cutinase (so-called CUTE plants) or lipase as well as several A. thaliana mutants with altered cuticular structure remained free of symptoms after an inoculation with Botrytis cinerea. The alterations in cuticular structure lead to the release of fungitoxic substances and changes in gene expression that form a multifactorial defence response. Several models to explain this syndrome are discussed.

Gene expression variation and expression quantitative trait mapping of human chromosome 21 genes.

Inter-individual differences in gene expression are likely to account for an important fraction of phenotypic differences, including susceptibility to common disorders. Recent studies have shown extensive variation in gene expression levels in humans and other organisms, and that a fraction of this variation is under genetic control. We investigated the patterns of gene expression variation in a 25 Mb region of human chromosome 21, which has been associated with many Down syndrome (DS) phenotypes. Taqman real-time PCR was used to measure expression variation of 41 genes in lymphoblastoid cells of 40 unrelated individuals. For 25 genes found to be differentially expressed, additional analysis was performed in 10 CEPH families to determine heritabilities and map loci harboring regulatory variation. Seventy-six percent of the differentially expressed genes had significant heritabilities, and genomewide linkage analysis led to the identification of significant eQTLs for nine genes. Most eQTLs were in trans, with the best result (P=7.46 x 10(-8)) obtained for TMEM1 on chromosome 12q24.33. A cis-eQTL identified for CCT8 was validated by performing an association study in 60 individuals from the HapMap project. SNP rs965951 located within CCT8 was found to be significantly associated with its expression levels (P=2.5 x 10(-5)) confirming cis-regulatory variation. The results of our study provide a representative view of expression variation of chromosome 21 genes, identify loci involved in their regulation and suggest that genes, for which expression differences are significantly larger than 1.5-fold in control samples, are unlikely to be involved in DS-phenotypes present in all affected individuals.

Involvement of PPAR nuclear receptors in tissue injury and wound repair.

Tissue damage resulting from chemical, mechanical, and biological injury, or from interrupted blood flow and reperfusion, is often life threatening. The subsequent tissue response involves an intricate series of events including inflammation, oxidative stress, immune cell recruitment, and cell survival, proliferation, migration, and differentiation. In addition, fibrotic repair characterized by myofibroblast transdifferentiation and the deposition of ECM proteins is activated. Failure to initiate, maintain, or stop this repair program has dramatic consequences, such as cell death and associated tissue necrosis or carcinogenesis. In this sense, inflammation and oxidative stress, which are beneficial defense processes, can become harmful if they do not resolve in time. This repair program is largely based on rapid and specific changes in gene expression controlled by transcription factors that sense injury. PPARs are such factors and are activated by lipid mediators produced after wounding. Here we highlight advances in our understanding of PPAR action during tissue repair and discuss the potential for these nuclear receptors as therapeutic targets for tissue injury.

Unusual astrocyte reactivity caused by the food mycotoxin ochratoxin A in aggregating rat brain cell cultures.

Ochratoxin A (OTA), a mycotoxin and widespread food contaminant, is known for its patent nephrotoxicity and potential neurotoxicity. Previous observations in vitro showed that in the CNS, glial cells were particularly sensitive to OTA. In the search for the molecular mechanisms underlying OTA neurotoxicity, we investigated the relationship between OTA toxicity and glial reactivity, in serum-free aggregating brain cell cultures. Using quantitative reverse transcriptase-polymerase chain reaction to analyze changes in gene expression, we found that in astrocytes, non cytotoxic concentrations of OTA down-regulated glial fibrillary acidic protein, while it up-regulated vimentin and the peroxisome proliferator-activated receptor-gamma expression. OTA also up-regulated the inducible nitric oxide synthase and the heme oxygenase-1. These OTA-induced alterations in gene expression were more pronounced in cultures at an advanced stage of maturation. The natural peroxisome proliferator-activated receptor-gamma ligand, 15-deoxy-delta(12,14) prostaglandin J2, and the cyclic AMP analog, bromo cyclic AMP, significantly attenuated the strong induction of peroxisome proliferator-activated receptor-gamma and inducible nitric oxide synthase, while they partially reversed the inhibitory effect of OTA on glial fibrillary acidic protein. The present results show that OTA affects the cytoskeletal integrity of astrocytes as well as the expression of genes pertaining to the brain inflammatory response system, and suggest that a relationship exists between the inflammatory events and the cytoskeletal changes induced by OTA. Furthermore, these results suggest that, by inducing an atypical glial reactivity, OTA may severely affect the neuroprotective capacity of glial cells.

Functional characterization of E- and P-cadherin in invasive breast cancer cells

BACKGROUND Alterations in the cadherin-catenin adhesion complexes are involved in tumor initiation, progression and metastasis. However, the functional implication of distinct cadherin types in breast cancer biology is still poorly understood. METHODS To compare the functional role of E-cadherin and P-cadherin in invasive breast cancer, we stably transfected these molecules into the MDA-MB-231 cell line, and investigated their effects on motility, invasion and gene expression regulation. RESULTS Expression of either E- and P-cadherin significantly increased cell aggregation and induced a switch from fibroblastic to epithelial morphology. Although expression of these cadherins did not completely reverse the mesenchymal phenotype of MDA-MB-231 cells, both E- and P-cadherin decreased fibroblast-like migration and invasion through extracellular matrix in a similar way. Moreover, microarray gene expression analysis of MDA-MB-231 cells after expression of E- and P-cadherins revealed that these molecules can activate signaling pathways leading to significant changes in gene expression. Although the expression patterns induced by E- and P-cadherin showed more similarities than differences, 40 genes were differentially modified by the expression of either cadherin type. CONCLUSION E- and P-cadherin have similar functional consequences on the phenotype and invasive behavior of MDA-MB-231 cells. Moreover, we demonstrate for the first time that these cadherins can induce both common and specific gene expression programs on invasive breast cancer cells. Importantly, these identified genes are potential targets for future studies on the functional consequences of altered cadherin expression in human breast cancer.

The cuticle: Not only a barrier for plant defence: A novel defence syndrome in plants with cuticular defects.

The cuticle is a physical barrier that prevents water loss and protects against irradiation, xenobiotics and pathogens. This classic textbook statement has recently been revisited and several observations were made showing that this dogma falls short of being universally true. Both transgenic Arabidopsis thaliana lines expressing cell wall-targeted fungal cutinase (so-called CUTE plants) or lipase as well as several A. thaliana mutants with altered cuticular structure remained free of symptoms after an inoculation with Botrytis cinerea. The alterations in cuticular structure lead to the release of fungitoxic substances and changes in gene expression that form a multifactorial defence response. Several models to explain this syndrome are discussed.

Global transcriptional programs in peripheral nerve endoneurium and DRG are resistant to the onset of type 1 diabetic neuropathy in Ins2 mice.

While the morphological and electrophysiological changes underlying diabetic peripheral neuropathy (DPN) are relatively well described, the involved molecular mechanisms remain poorly understood. In this study, we investigated whether phenotypic changes associated with early DPN are correlated with transcriptional alterations in the neuronal (dorsal root ganglia [DRG]) or the glial (endoneurium) compartments of the peripheral nerve. We used Ins2(Akita/+) mice to study transcriptional changes underlying the onset of DPN in type 1 diabetes mellitus (DM). Weight, blood glucose and motor nerve conduction velocity (MNCV) were measured in Ins2(Akita/+) and control mice during the first three months of life in order to determine the onset of DPN. Based on this phenotypic characterization, we performed gene expression profiling using sciatic nerve endoneurium and DRG isolated from pre-symptomatic and early symptomatic Ins2(Akita/+) mice and sex-matched littermate controls. Our phenotypic analysis of Ins2(Akita/+) mice revealed that DPN, as measured by reduced MNCV, is detectable in affected animals already one week after the onset of hyperglycemia. Surprisingly, the onset of DPN was not associated with any major persistent changes in gene expression profiles in either sciatic nerve endoneurium or DRG. Our data thus demonstrated that the transcriptional programs in both endoneurial and neuronal compartments of the peripheral nerve are relatively resistant to the onset of hyperglycemia and hypoinsulinemia suggesting that either minor transcriptional alterations or changes on the proteomic level are responsible for the functional deficits associated with the onset of DPN in type 1 DM.

Neofunctionalization in vertebrates: the example of retinoic acid receptors.

Understanding the role of gene duplications in establishing vertebrate innovations is one of the main challenges of Evo-Devo (evolution of development) studies. Data on evolutionary changes in gene expression (i.e., evolution of transcription factor-cis-regulatory elements relationships) tell only part of the story; protein function, best studied by biochemical and functional assays, can also change. In this study, we have investigated how gene duplication has affected both the expression and the ligand-binding specificity of retinoic acid receptors (RARs), which play a major role in chordate embryonic development. Mammals have three paralogous RAR genes--RAR alpha, beta, and gamma--which resulted from genome duplications at the origin of vertebrates. By using pharmacological ligands selective for specific paralogues, we have studied the ligand-binding capacities of RARs from diverse chordates species. We have found that RAR beta-like binding selectivity is a synapomorphy of all chordate RARs, including a reconstructed synthetic RAR representing the receptor present in the ancestor of chordates. Moreover, comparison of expression patterns of the cephalochordate amphioxus and the vertebrates suggests that, of all the RARs, RAR beta expression has remained most similar to that of the ancestral RAR. On the basis of these results together, we suggest that while RAR beta kept the ancestral RAR role, RAR alpha and RAR gamma diverged both in ligand-binding capacity and in expression patterns. We thus suggest that neofunctionalization occurred at both the expression and the functional levels to shape RAR roles during development in vertebrates.

Large scale assessment of regulatory evolution and transcriptome complexity in mammals

AbstractIn addition to genetic changes affecting the function of gene products, changes in gene expression have been suggested to underlie many or even most of the phenotypic differences among mammals. However, detailed gene expression comparisons were, until recently, restricted to closely related species, owing to technological limitations. Thus, we took advantage of the latest technologies (RNA-Seq) to generate extensive qualitative and quantitative transcriptome data for a unique collection of somatic and germline tissues from representatives of all major mammalian lineages (placental mammals, marsupials and monotremes) and birds, the evolutionary outgroup.In the first major project of my thesis, we performed global comparative analyses of gene expression levels based on these data. Our analyses provided fundamental insights into the dynamics of transcriptome change during mammalian evolution (e.g., the rate of expression change across species, tissues and chromosomes) and allowed the exploration of the functional relevance and phenotypic implications of transcription changes at a genome-wide scale (e.g., we identified numerous potentially selectively driven expression switches).In a second project of my thesis, which was also based on the unique transcriptome data generated in the context of the first project we focused on the evolution of alternative splicing in mammals. Alternative splicing contributes to transcriptome complexity by generating several transcript isoforms from a single gene, which can, thus, perform various functions. To complete the global comparative analysis of gene expression changes, we explored patterns of alternative splicing evolution. This work uncovered several general and unexpected patterns of alternative splicing evolution (e.g., we found that alternative splicing evolves extremely rapidly) as well as a large number of conserved alternative isoforms that may be crucial for the functioning of mammalian organs.Finally, the third and final project of my PhD consisted in analyzing in detail the unique functional and evolutionary properties of the testis by exploring the extent of its transcriptome complexity. This organ was previously shown to evolve rapidly both at the phenotypic and molecular level, apparently because of the specific pressures that act on this organ and are associated with its reproductive function. Moreover, my analyses of the amniote tissue transcriptome data described above, revealed strikingly widespread transcriptional activity of both functional and nonfunctional genomic elements in the testis compared to the other organs. To elucidate the cellular source and mechanisms underlying this promiscuous transcription in the testis, we generated deep coverage RNA-Seq data for all major testis cell types as well as epigenetic data (DNA and histone methylation) using the mouse as model system. The integration of these complete dataset revealed that meiotic and especially post-meiotic germ cells are the major contributors to the widespread functional and nonfunctional transcriptome complexity of the testis, and that this "promiscuous" spermatogenic transcription is resulting, at least partially, from an overall transcriptionally permissive chromatin state. We hypothesize that this particular open state of the chromatin results from the extensive chromatin remodeling that occurs during spermatogenesis which ultimately leads to the replacement of histones by protamines in the mature spermatozoa. Our results have important functional and evolutionary implications (e.g., regarding new gene birth and testicular gene expression evolution).Generally, these three large-scale projects of my thesis provide complete and massive datasets that constitute valuables resources for further functional and evolutionary analyses of mammalian genomes.

Effects of the PPAR-beta agonist GW501516 in an in vitro model of brain inflammation and antibody-induced demyelination.

BACKGROUND: Brain inflammation plays a central role in numerous brain pathologies, including multiple sclerosis (MS). Microglial cells and astrocytes are the effector cells of neuroinflammation. They can be activated also by agents such as interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS). Peroxisome proliferator-associated receptor (PPAR) pathways are involved in the control of the inflammatory processes, and PPAR-beta seems to play an important role in the regulation of central inflammation. In addition, PPAR-beta agonists were shown to have trophic effects on oligodendrocytes in vitro, and to confer partial protection in experimental autoimmune encephalomyelitis (EAE), an animal model of MS. In the present work, a three-dimensional brain cell culture system was used as in vitro model to study antibody-induced demyelination and inflammatory responses. GW 501516, a specific PPAR-beta agonist, was examined for its capacity to protect from antibody-mediated demyelination and to prevent inflammatory responses induced by IFN-gamma and LPS. METHODS: Aggregating brain cells cultures were prepared from embryonal rat brain, and used to study the inflammatory responses triggered by IFN-gamma and LPS and by antibody-mediated demyelination induced by antibodies directed against myelin-oligodendrocyte glycoprotein (MOG). The effects of GW 501516 on cellular responses were characterized by the quantification of the mRNA expression of tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), inducible NO synthase (i-NOS), PPAR-beta, PPAR-gamma, glial fibrillary acidic protein (GFAP), myelin basic protein (MBP), and high molecular weight neurofilament protein (NF-H). GFAP expression was also examined by immunocytochemistry, and microglial cells were visualized by isolectin B4 (IB4) and ED1 labeling. RESULTS: GW 501516 decreased the IFN-gamma-induced up-regulation of TNF-alpha and iNOS in accord with the proposed anti-inflammatory effects of this PPAR-beta agonist. However, it increased IL-6 m-RNA expression. In demyelinating cultures, reactivity of both microglial cells and astrocytes was observed, while the expression of the inflammatory cytokines and iNOS remained unaffected. Furthermore, GW 501516 did not protect against the demyelination-induced changes in gene expression. CONCLUSION: Although GW 501516 showed anti-inflammatory activity, it did not protect against antibody-mediated demyelination. This suggests that the protective effects of PPAR-beta agonists observed in vivo can be attributed to their anti-inflammatory properties rather than to a direct protective or trophic effect on oligodendrocytes.

Loss of mitochondrial functions associated with azole resistance in Candida glabrata results in enhanced virulence in mice.

Mitochondrial dysfunction is one of the possible mechanisms by which azole resistance can occur in Candida glabrata. Cells with mitochondrial DNA deficiency (so-called "petite mutants") upregulate ATP binding cassette (ABC) transporter genes and thus display increased resistance to azoles. Isolation of such C. glabrata mutants from patients receiving antifungal therapy or prophylaxis has been rarely reported. In this study, we characterized two sequential and related C. glabrata isolates recovered from the same patient undergoing azole therapy. The first isolate (BPY40) was azole susceptible (fluconazole MIC, 4 μg/ml), and the second (BPY41) was azole resistant (fluconazole MIC, >256 μg/ml). BPY41 exhibited mitochondrial dysfunction and upregulation of the ABC transporter genes C. glabrata CDR1 (CgCDR1), CgCDR2, and CgSNQ2. We next assessed whether mitochondrial dysfunction conferred a selective advantage during host infection by testing the virulence of BPY40 and BPY41 in mice. Surprisingly, even with in vitro growth deficiency compared to BPY40, BPY41 was more virulent (as judged by mortality and fungal tissue burden) than BPY40 in both systemic and vaginal murine infection models. The increased virulence of the petite mutant correlated with a drastic gain of fitness in mice compared to that of its parental isolate. To understand this unexpected feature, genome-wide changes in gene expression driven by the petite mutation were analyzed by use of microarrays during in vitro growth. Enrichment of specific biological processes (oxido-reductive metabolism and the stress response) was observed in BPY41, all of which was consistent with mitochondrial dysfunction. Finally, some genes involved in cell wall remodelling were upregulated in BPY41 compared to BPY40, which may partially explain the enhanced virulence of BPY41. In conclusion, this study shows for the first time that mitochondrial dysfunction selected in vivo under azole therapy, even if strongly affecting in vitro growth characteristics, can confer a selective advantage under host conditions, allowing the C. glabrata mutant to be more virulent than wild-type isolates.

Long-term changes in synaptic transmission of the lateral amygdala induced by strong "in vitro" activation

Résumé : L'amygdale latérale (AL) joue un .rôle essentiel dans la plasticité synaptique à la base du conditionnement de la peur. Malgré le faite que la majorité des cellules de l'AL reçoivent les afférentes nécessaires, une potentialisation dans seulement une partie d'entre elles est obligatoire afin que l'apprentissage de la peur ait lieu. Il a été montré que ces cellules expriment la forme active de CREB, et celui-ci a été associé aux cellules dites de type 'nonaccomrnodating' (nAC). Très récemment, une étude a impliqué les circuits récurrents de l'AL dans le conditionnement de la peur. Un lien entre ces deux observations n'a toutefois jamais été établi. t Nous avons utilisé un protocole in vitro de forte activation de l'AL, résultant dans l'induction de 'bursts' provenant de l'hippocampe et se propageant jusqu'à l'AL. Dans l'AL ces 'bursts' atteignent toutes les cellules et se propagent à travers plusieurs chemins. Utilisant ce protocole, nous avons, pour la première fois pu associer dans l'AL, des cellules connectées de manière récurrente avec des cellules de type nAC. Aussi bien dans ces dernières que dans les cellules de type 'accommodating' (AC), une diminution dans la transmission inhibitrice, à la fois exprimée de manière pré synaptique mais également indépendant de la synthèse de protéine a pu être observé. Au contraire, une potentialisation induite et exprimée au niveau pré synaptique ainsi que dépendante de la synthèse de protéine a pu être trouvé uniquement dans les cellules de type nAC. De plus, une hyperexcitabilité, dépendante des récepteurs NMDA a pu être observé, avec une sélection préférentielle des cellules du type nAC dans la génération de bursts. Nous avons également pu démontrer que la transformation d'un certain nombre de cellules de type AC en cellules dites nAC accompagnait cette augmentation générale de l'excitabilité de l'AL. Du faite da la grande quantité d'indices suggérant une connexion entre le système noradrénergique et les états de peur/d'anxiété, les effets d'une forte activation de l'AL sur ce dernier ont été investigués et ont révélés une perte de sa capacité de modulation du 'spiking pattern'. Finalement, des changements au niveau de l'expression d'un certain nombre de gènes, incluant celui codant pour le BDNF, a pu être trouvé à la suite d'une forte activation de l'AL. En raison du lien récemment décrit entre l'expression de la forme active de CREB et des cellules de type nAC ainsi que celui de l'implication des cellules de l'AL connectés de manière récurrente dans l'apprentissage de la peur, nos résultats nous permettent de suggérer un modèle expliquant comment la potentialisation des connections récurrentes entre cellules de type nAC pourrait être à la base de leur recrutement sélectif pendant le conditionnement de la peur. De plus, ils peuvent offrir des indices par rapport aux mécanismes à travers lesquels une sous population de neurones peut être réactivée par une stimulation externe précédemment inefficace, et induire ainsi un signal suffisamment fort pour qu'il soit transmit aux structures efférentes de l'AL. Abstract : The lateral nucleus of the amygdala (LA) is critically involved in the plasticity underlying fear-conditioned learning (Sah et al., 2008). Even though the majority of cells in the LA receive the necessary sensory inputs, potentiation in only a subset is required for fear learning to occur (Repa et al., 2001; Rumpel et al., 2005). These cells express active CREB (CAMP-responsive element-binding protein) (Han et al., 200, and this was related to the non-accommodating (nAC) spiking phenotype (Viosca et al., 2009; Zhou et al., 2009). In addition, a very recent study implicated recurrently connected cells of the LA in fear conditioned learning (Johnson et al., 2008). A link between the two observations has however never been made. In rats, we used an in vitro protocol of strong activation of the LA, resulting in bursting activity, which spread from the hippocampus to the LA. Within the LA, this activity reached all cells and spread via a multitude of pathways. Using this model, we were able to link, for the first time, recurrently connected cells in the LA with cells of the nAC phenotype. While we found a presynaptically expressed, protein synthesis independent decrease in inhibitory synaptic transmission in both nAC and accommodating (AC) cells, only nAC cells underwent a presynaptically induced and expressed, protein synthesis dependent potentiation. Moreover we observed an NMDA dependent hyperexcitability of the LA, with a preferential selection of nAC cells into burst generation. The transformation of a subset of AC cells into nAC cells accompanied this general increase in LA excitability. Given the considerable evidence suggesting a relationship between the central noradrenergic (NA) system and fear/anxiety states (Itoi, 2008), the effects of strong activation of the LA on the noradrenergic system were investigated, which revealed a loss of its modulatory actions on cell spiking patterns. Finally, we found changes in the expression levels of a number of genes; among which the one coding for $DNF, to be induced by strong activation of the LA. In view of the recently described link between nAC cells and expression of pCREB (phosphorylated cAMP-responsive element-binding protein) as well as the involvement of recurrently connected cells of the LA in fear-conditioned learning, our findings may provide a model of how potentiation of recurrent connections between nAC neurons underlies their recruitment into the fear memory trace. Additionally, they may offer clues as to the mechanisms through which a selected subset of neurons can be reactivated by smaller, previously ineffective external stimulations to respond with a sufficiently strong signal, which can be transmitted to downstream targets of the LA.

Global transcriptional programs in peripheral nerve endoneurium and DRG are resistant to the onset of type 1 diabetic neuropathy in Ins2 mice.

While the morphological and electrophysiological changes underlying diabetic peripheral neuropathy (DPN) are relatively well described, the involved molecular mechanisms remain poorly understood. In this study, we investigated whether phenotypic changes associated with early DPN are correlated with transcriptional alterations in the neuronal (dorsal root ganglia [DRG]) or the glial (endoneurium) compartments of the peripheral nerve. We used Ins2(Akita/+) mice to study transcriptional changes underlying the onset of DPN in type 1 diabetes mellitus (DM). Weight, blood glucose and motor nerve conduction velocity (MNCV) were measured in Ins2(Akita/+) and control mice during the first three months of life in order to determine the onset of DPN. Based on this phenotypic characterization, we performed gene expression profiling using sciatic nerve endoneurium and DRG isolated from pre-symptomatic and early symptomatic Ins2(Akita/+) mice and sex-matched littermate controls. Our phenotypic analysis of Ins2(Akita/+) mice revealed that DPN, as measured by reduced MNCV, is detectable in affected animals already one week after the onset of hyperglycemia. Surprisingly, the onset of DPN was not associated with any major persistent changes in gene expression profiles in either sciatic nerve endoneurium or DRG. Our data thus demonstrated that the transcriptional programs in both endoneurial and neuronal compartments of the peripheral nerve are relatively resistant to the onset of hyperglycemia and hypoinsulinemia suggesting that either minor transcriptional alterations or changes on the proteomic level are responsible for the functional deficits associated with the onset of DPN in type 1 DM.