Membrane depolarization and calcium induce c-fos transcription via phosphorylation of transcription factor CREB

Emerging themes in neuronal activity-dependent gene expression

In this review, we attempt to discuss emerging themes in the regulation of neuronal activity-regulated genes, focusing primarily on an important subset of immediate-early genes. We first discuss earlier studies that have illuminated the role of cis-acting elements within the promoters of immediate-early genes, the corresponding transcription factors that bind these elements, and the roles of major activity-regulated signaling pathways. However, our emphasis is on new studies that have revealed an important role for epigenetic and topological mechanisms, including enhancer-promoter interactions, enhancer RNAs (eRNAs), and activity-induced DNA breaks, that have emerged as important factors that govern the temporal dynamics of activity-induced gene transcription.

Familiarity with a vocal category biases the compartmental expression of Arc/Arg3.1 in core auditory cortex

Learning to recognize a stimulus category requires experience with its many natural variations. However, the mechanisms that allow a category's sensorineural representation to be updated after experiencing new exemplars are not well understood, particularly at the molecular level. Here we investigate how a natural vocal category induces expression in the auditory system of a key synaptic plasticity effector immediate early gene, Arc/Arg3.1, which is required for memory consolidation. We use the ultrasonic communication system between mouse pups and adult females to study whether prior familiarity with pup vocalizations alters how Arc is engaged in the core auditory cortex after playback of novel exemplars from the pup vocal category. A computerized, 3D surface-assisted cellular compartmental analysis, validated against manual cell counts, demonstrates significant changes in the recruitment of neurons expressing Arc in pup-experienced animals (mothers and virgin females "cocaring" for pups) compared with pup-inexperienced animals (pup-naïve virgins), especially when listening to more familiar, natural calls compared to less familiar but similarly recognized tonal model calls. Our data support the hypothesis that the kinetics of Arc induction to refine cortical representations of sensory categories is sensitive to the familiarity of the sensory experience.

The Insula and Taste Learning

The sense of taste is a key component of the sensory machinery, enabling the evaluation of both the safety as well as forming associations regarding the nutritional value of ingestible substances. Indicative of the salience of the modality, taste conditioning can be achieved in rodents upon a single pairing of a tastant with a chemical stimulus inducing malaise. This robust associative learning paradigm has been heavily linked with activity within the insular cortex (IC), among other regions, such as the amygdala and medial prefrontal cortex. A number of studies have demonstrated taste memory formation to be dependent on protein synthesis at the IC and to correlate with the induction of signaling cascades involved in synaptic plasticity. Taste learning has been shown to require the differential involvement of dopaminergic GABAergic, glutamatergic, muscarinic neurotransmission across an extended taste learning circuit. The subsequent activation of downstream protein kinases (ERK, CaMKII), transcription factors (CREB, Elk-1) and immediate early genes (c-fos, Arc), has been implicated in the regulation of the different phases of taste learning. This review discusses the relevant neurotransmission, molecular signaling pathways and genetic markers involved in novel and aversive taste learning, with a particular focus on the IC. Imaging and other studies in humans have implicated the IC in the pathophysiology of a number of cognitive disorders. We conclude that the IC participates in circuit-wide computations that modulate the interception and encoding of sensory information, as well as the formation of subjective internal representations that control the expression of motivated behaviors.

Progesterone improves neurocognitive outcomes following therapeutic cranial irradiation in mice

Despite improved therapeutic methods, CNS toxicity resulting from cancer treatment remains a major cause of post-treatment morbidity. More than half of adult patients with cranial irradiation for brain cancer develop neurobehavioral/cognitive deficits that severely impact quality of life. We examined the neuroprotective effects of the neurosteroid progesterone (PROG) against ionizing radiation (IR)-induced neurobehavioral/cognitive deficits in mice. Male C57/BL mice were exposed to one of two fractionated dose regimens of IR (3Gy×3 or 3Gy×5). PROG (16mg/kg; 0.16mg/g) was given as a pre-, concurrent or post-IR treatment for 14days. Mice were tested for short- and long-term effects of IR and PROG on neurobehavioral/cognitive function on days 10 and 30 after IR treatment. We evaluated both hippocampus-dependent and -independent memory functions. Locomotor activity, elevated plus maze, novel object recognition and Morris water maze tests revealed behavioral deficits following IR. PROG treatment produced improvement in behavioral performance at both time points in the mice given IR. Western blot analysis of hippocampal and cortical tissue showed that IR at both doses induced astrocytic activation (glial fibrillary acidic protein), reactive macrophages/microglia (CD68) and apoptosis (cleaved caspase-3) and PROG treatment inhibited these markers of brain injury. There was no significant difference in the degree of deficit in any test between the two dose regimens of IR at either time point. These findings could be important in the context of patients with brain tumors who may undergo radiotherapy and eventually develop cognitive deficits.

Oxytocin attenuates deficits in social interaction but not recognition memory in a prenatal valproic acid-induced mouse model of autism

Recent studies have reported that oxytocin ameliorates behavioral abnormalities in both animal models and individuals with autism spectrum disorders (ASD). However, the mechanisms underlying the ameliorating effects of oxytocin remain unclear. In this study, we examined the effects of intranasal oxytocin on impairments in social interaction and recognition memory in an ASD mouse model in which animals are prenatally exposed to valproic acid (VPA). We found that a single intranasal administration of oxytocin restored social interaction deficits for up to 2h in mice prenatally exposed to VPA, but there was no effect on recognition memory impairments. Additionally, administration of oxytocin across 2weeks improved prenatal VPA-induced social interaction deficits for at least 24h. In contrast, there were no effects on the time spent sniffing in control mice. Immunohistochemical analysis revealed that intranasal administration of oxytocin increased c-Fos expression in the paraventricular nuclei (PVN), prefrontal cortex, and somatosensory cortex, but not the hippocampal CA1 and CA3 regions of VPA-exposed mice, suggesting the former regions may underlie the effects of oxytocin. These findings suggest that oxytocin attenuates social interaction deficits through the activation of higher cortical areas and the PVN in an ASD mouse model.

Transgenic mice lacking CREB and CREM in noradrenergic and serotonergic neurons respond differently to common antidepressants on tail suspension test

Evidence exists that chronic antidepressant therapy enhances CREB levels and activity. Nevertheless, the data are not conclusive, as previous analysis of transgenic mouse models has suggested that CREB inactivation in fact contributes to antidepressant-like behavior. The aim of this study was to evaluate the role of CREB in this context by exploiting novel transgenic mouse models, characterized by selective ablation of CREB restricted to noradrenergic (Creb1^DBHCre/Crem−/−) or serotonergic (Creb1^TPH2CreERT2/Crem−/−) neurons in a CREM-deficient background to avoid possible compensatory effects of CREM. Selective and functional ablation of CREB affected antidepressant-like behavior in a tail suspension test (TST) after antidepressant treatment. Contrary to single Creb1^DBHCre mutants, Creb1^DBHCre/Crem−/− mice did not respond to acute desipramine administration (20 mg/kg) on the TST. On the other hand, single Creb1^TPH2CreERT2 mutants displayed reduced responses to fluoxetine (10 mg/kg) on the TST, while the effects in Creb1^TPH2CreERT2/Crem−/− mice differed by gender. Our results provide further evidence for the important role of CREM as a compensatory factor. Additionally, the results indicate that new models based on the functional ablation of CREB in select neuronal populations may represent a valuable tool for investigating the role of CREB in the mechanism of antidepressant therapy.

Long-term restoration of visual function in end-stage retinal degeneration using subretinal human melanopsin gene therapy

Optogenetic strategies to restore vision in patients who are blind from end-stage retinal degenerations aim to render remaining retinal cells light sensitive once photoreceptors are lost. Here, we assessed long-term functional outcomes following subretinal delivery of the human melanopsin gene (OPN4) in the rd1 mouse model of retinal degeneration using an adeno-associated viral vector. Ectopic expression of OPN4 using a ubiquitous promoter resulted in cellular depolarization and ganglion cell action potential firing. Restoration of the pupil light reflex, behavioral light avoidance, and the ability to perform a task requiring basic image recognition were restored up to 13 mo following injection. These data suggest that melanopsin gene therapy via a subretinal route may be a viable and stable therapeutic option for the treatment of end-stage retinal degeneration in humans.

Analysis of lipid raft molecules in the living brain slices

Neuronal plasma membrane has been thought to retain a lot of lipid raft components which play important roles in the neural function. Although the biochemical analyses of lipid raft using brain tissues have been extensively carried out in the past 20 years, many of their experimental conditions do not coincide with those of standard neuroscience researches such as neurophysiology and neuropharmacology. Hence, the physiological methods for lipid raft analysis that can be compatible with general neuroscience have been required. Herein, we developed a system to physiologically analyze ganglioside GM1-enriched lipid rafts in brain tissues using the "Enzyme-Mediated Activation of Radical Sources (EMARS)" method that we reported (Kotani N. et al. Proc. Natl. Acad. Sci. U S A 105, 7405-7409 (2008)). The EMARS method was applied to acute brain slices prepared from mouse brains in aCSF solution using the EMARS probe, HRP-conjugated cholera toxin subunit B, which recognizes ganglioside GM1. The membrane molecules present in the GM1-enriched lipid rafts were then labeled with fluorescein under the physiological condition. The fluorescein-tagged lipid raft molecules called "EMARS products" distributed differentially among various parts of the brain. On the other hand, appreciable differences were not detected among segments along the longitudinal axis of the hippocampus. We further developed a device to label the lipid raft molecules in acute hippocampal slices under two different physiological conditions to detect dynamics of the lipid raft molecules during neural excitation. Using this device, several cell membrane molecules including Thy1, known as a lipid raft resident molecule in neurons, were confirmed by the EMARS method in living hippocampal slices.

Neuroplasticity pathways and protein-interaction networks are modulated by vortioxetine in rodents

Background

The identification of biomarkers that predict susceptibility to major depressive disorder and treatment response to antidepressants is a major challenge. Vortioxetine is a novel multimodal antidepressant that possesses pro-cognitive properties and differentiates from other conventional antidepressants on various cognitive and plasticity measures. The aim of the present study was to identify biological systems rather than single biomarkers that may underlie vortioxetine’s treatment effects.

Results

We show that the biological systems regulated by vortioxetine are overlapping between mouse and rat in response to distinct treatment regimens and in different brain regions. Furthermore, analysis of complexes of physically-interacting proteins reveal that biomarkers involved in transcriptional regulation, neurodevelopment, neuroplasticity, and endocytosis are modulated by vortioxetine. A subsequent qPCR study examining the expression of targets in the protein–protein interactome space in response to chronic vortioxetine treatment over a range of doses provides further biological validation that vortioxetine engages neuroplasticity networks. Thus, the same biology is regulated in different species and sexes, different brain regions, and in response to distinct routes of administration and regimens.

Conclusions

A recurring theme, based on the present study as well as previous findings, is that networks related to synaptic plasticity, synaptic transmission, signal transduction, and neurodevelopment are modulated in response to vortioxetine treatment. Regulation of these signaling pathways by vortioxetine may underlie vortioxetine’s cognitive-enhancing properties.

Electronic supplementary material

The online version of this article (doi:10.1186/s12868-017-0376-x) contains supplementary material, which is available to authorized users.

Activation of the CREB/c-Fos Pathway during Long-Term Synaptic Plasticity in the Cerebellum Granular Layer

The induction of long-term potentiation and depression (LTP and LTD) is thought to trigger gene expression and protein synthesis, leading to consolidation of synaptic and neuronal changes. However, while LTP and LTD have been proposed to play important roles for sensori-motor learning in the cerebellum granular layer, their association with these mechanisms remained unclear. Here, we have investigated phosphorylation of the cAMP-responsive element binding protein (CREB) and activation of the immediate early gene c-Fos pathway following the induction of synaptic plasticity by theta-burst stimulation (TBS) in acute cerebellar slices. LTP and LTD were localized using voltage-sensitive dye imaging (VSDi). At two time points following TBS (15 min and 120 min), corresponding to the early and late phases of plasticity, slices were fixed and processed to evaluate CREB phosphorylation (P-CREB) and c-FOS protein levels, as well as Creb and c-Fos mRNA expression. High levels of P-CREB and Creb/c-Fos were detected before those of c-FOS, as expected if CREB phosphorylation triggered gene expression followed by protein synthesis. No differences between control slices and slices stimulated with TBS were observed in the presence of an N-methyl-D-aspartate receptor (NMDAR) antagonist. Interestingly, activation of the CREB/c-Fos system showed a relevant degree of colocalization with long-term synaptic plasticity. These results show that NMDAR-dependent plasticity at the cerebellum input stage bears about transcriptional and post-transcriptional processes potentially contributing to cerebellar learning and memory consolidation.

Transient acidosis while retrieving a fear-related memory enhances its lability

Attenuating the strength of fearful memories could benefit people disabled by memories of past trauma. Pavlovian conditioning experiments indicate that a retrieval cue can return a conditioned aversive memory to a labile state. However, means to enhance retrieval and render a memory more labile are unknown. We hypothesized that augmenting synaptic signaling during retrieval would increase memory lability. To enhance synaptic transmission, mice inhaled CO2 to induce an acidosis and activate acid sensing ion channels. Transient acidification increased the retrieval-induced lability of an aversive memory. The labile memory could then be weakened by an extinction protocol or strengthened by reconditioning. Coupling CO2 inhalation to retrieval increased activation of amygdala neurons bearing the memory trace and increased the synaptic exchange from Ca2+-impermeable to Ca2+-permeable AMPA receptors. The results suggest that transient acidosis during retrieval renders the memory of an aversive event more labile and suggest a strategy to modify debilitating memories.

Brain networks activated to form object recognition memory

Object recognition memory allows discrimination of familiar and novel objects. Previous studies have shown the importance of several brain regions for object recognition memories; however, the mechanisms underlying the consolidation of object recognition (OR) memory at the anatomic level remain unknown. Here, we analyzed the brain network for the generation of OR memory in mice by measuring the expression of the immediate-early gene c-fos. We found that c-fos expression was induced in the hippocampus (CA1 and CA3 regions), insular cortex (IC), perirhinal cortex (PRh), and medial prefrontal cortex (mPFC) when OR memory was generated, suggesting that gene expression in these brain regions contributes to the formation of OR memory. Consistently, inhibition of protein synthesis in the mPFC blocked the formation of long-term OR memory. Importantly, network analyses suggested that the hippocampus, IC, PRh and mPFC show increased connectivity with other brain regions when OR memory is formed. Thus, we suggest that a brain network composed of the hippocampus, IC, PRh, and mPFC is required for the generation of OR memory by connecting with other brain regions.

Altered learning, memory, and social behavior in type 1 taste receptor subunit 3 knock-out mice are associated with neuronal dysfunction

The type 1 taste receptor member 3 (T1R3) is a G protein-coupled receptor involved in sweet-taste perception. Besides the tongue, the T1R3 receptor is highly expressed in brain areas implicated in cognition, including the hippocampus and cortex. As cognitive decline is often preceded by significant metabolic or endocrinological dysfunctions regulated by the sweet-taste perception system, we hypothesized that a disruption of the sweet-taste perception in the brain could have a key role in the development of cognitive dysfunction. To assess the importance of the sweet-taste receptors in the brain, we conducted transcriptomic and proteomic analyses of cortical and hippocampal tissues isolated from T1R3 knock-out (T1R3KO) mice. The effect of an impaired sweet-taste perception system on cognition functions were examined by analyzing synaptic integrity and performing animal behavior on T1R3KO mice. Although T1R3KO mice did not present a metabolically disrupted phenotype, bioinformatic interpretation of the high-dimensionality data indicated a strong neurodegenerative signature associated with significant alterations in pathways involved in neuritogenesis, dendritic growth, and synaptogenesis. Furthermore, a significantly reduced dendritic spine density was observed in T1R3KO mice together with alterations in learning and memory functions as well as sociability deficits. Taken together our data suggest that the sweet-taste receptor system plays an important neurotrophic role in the extralingual central nervous tissue that underpins synaptic function, memory acquisition, and social behavior.

Neurons and neuronal activity control gene expression in astrocytes to regulate their development and metabolism

The influence that neurons exert on astrocytic function is poorly understood. To investigate this, we first developed a system combining cortical neurons and astrocytes from closely related species, followed by RNA-seq and in silico species separation. This approach uncovers a wide programme of neuron-induced astrocytic gene expression, involving Notch signalling, which drives and maintains astrocytic maturity and neurotransmitter uptake function, is conserved in human development, and is disrupted by neurodegeneration. Separately, hundreds of astrocytic genes are acutely regulated by synaptic activity via mechanisms involving cAMP/PKA-dependent CREB activation. This includes the coordinated activity-dependent upregulation of major astrocytic components of the astrocyte-neuron lactate shuttle, leading to a CREB-dependent increase in astrocytic glucose metabolism and elevated lactate export. Moreover, the groups of astrocytic genes induced by neurons or neuronal activity both show age-dependent decline in humans. Thus, neurons and neuronal activity regulate the astrocytic transcriptome with the potential to shape astrocyte-neuron metabolic cooperation.

Functional Connectivity of Multiple Brain Regions Required for the Consolidation of Social Recognition Memory

Social recognition memory is an essential and basic component of social behavior that is used to discriminate familiar and novel animals/humans. Previous studies have shown the importance of several brain regions for social recognition memories; however, the mechanisms underlying the consolidation of social recognition memory at the molecular and anatomic levels remain unknown. Here, we show a brain network necessary for the generation of social recognition memory in mice. A mouse genetic study showed that cAMP-responsive element-binding protein (CREB)-mediated transcription is required for the formation of social recognition memory. Importantly, significant inductions of the CREB target immediate-early genes c-fos and Arc were observed in the hippocampus (CA1 and CA3 regions), medial prefrontal cortex (mPFC), anterior cingulate cortex (ACC), and amygdala (basolateral region) when social recognition memory was generated. Pharmacological experiments using a microinfusion of the protein synthesis inhibitor anisomycin showed that protein synthesis in these brain regions is required for the consolidation of social recognition memory. These findings suggested that social recognition memory is consolidated through the activation of CREB-mediated gene expression in the hippocampus/mPFC/ACC/amygdala. Network analyses suggested that these four brain regions show functional connectivity with other brain regions and, more importantly, that the hippocampus functions as a hub to integrate brain networks and generate social recognition memory, whereas the ACC and amygdala are important for coordinating brain activity when social interaction is initiated by connecting with other brain regions. We have found that a brain network composed of the hippocampus/mPFC/ACC/amygdala is required for the consolidation of social recognition memory.SIGNIFICANCE STATEMENT Here, we identify brain networks composed of multiple brain regions for the consolidation of social recognition memory. We found that social recognition memory is consolidated through CREB-meditated gene expression in the hippocampus, medial prefrontal cortex, anterior cingulate cortex (ACC), and amygdala. Importantly, network analyses based on c-fos expression suggest that functional connectivity of these four brain regions with other brain regions is increased with time spent in social investigation toward the generation of brain networks to consolidate social recognition memory. Furthermore, our findings suggest that hippocampus functions as a hub to integrate brain networks and generate social recognition memory, whereas ACC and amygdala are important for coordinating brain activity when social interaction is initiated by connecting with other brain regions.

The Life Span Model of Suicide and Its Neurobiological Foundation

The very incomprehensibility of the suicidal act has been occupying the minds of researchers and health professionals for a long time. Several theories of suicide have been proposed since the beginning of the past century, and a myriad of neurobiological studies have been conducted over the past two decades in order to elucidate its pathophysiology. Both neurobiology and psychological theories tend to work in parallel lines that need behavioral and empirical data respectively, to confirm their hypotheses. In this review, we are proposing a "Life Span Model of Suicide" with an attempt to integrate the "Stress-Diathesis Model" and the "Interpersonal Model of Suicide" into a neurobiological narrative and support it by providing a thorough compilation of related genetic, epigenetic, and gene expression findings. This proposed model comprises three layers, forming the capability of suicide: genetic factors as the predisposing Diathesis on one side and Stress, characterized by epigenetic marks on the other side, and in between gene expression and gene function which are thought to be influenced by Diathesis and Stress components. The empirical evidence of this model is yet to be confirmed and further research, specifically epigenetic studies in particular, are needed to support the presence of a life-long, evolving capability of suicide and identify its neurobiological correlates.

CREB at the Crossroads of Activity-Dependent Regulation of Nervous System Development and Function

The central nervous system is a highly plastic network of cells that constantly adjusts its functions to environmental stimuli throughout life. Transcription-dependent mechanisms modify neuronal properties to respond to external stimuli regulating numerous developmental functions, such as cell survival and differentiation, and physiological functions such as learning, memory, and circadian rhythmicity. The discovery and cloning of the cyclic adenosine monophosphate (cAMP) responsive element binding protein (CREB) constituted a big step toward deciphering the molecular mechanisms underlying neuronal plasticity. CREB was first discovered in learning and memory studies as a crucial mediator of activity-dependent changes in target gene expression that in turn impose long-lasting modifications of the structure and function of neurons. In this chapter, we review the molecular and signaling mechanisms of neural activity-dependent recruitment of CREB and its cofactors. We discuss the crosstalk between signaling pathways that imprints diverse spatiotemporal patterns of CREB activation allowing for the integration of a wide variety of stimuli.

A calcium-sensitive feed-forward loop regulating the expression of the ATP-gated purinergic P2X7 receptor via specificity protein 1 and microRNA-22

Cells have developed complex transcriptional regulatory mechanisms to maintain intracellular homeostasis and withstand pathophysiological stressors. Feed-forward loops comprising transcription factors that drive expression of both target gene and a microRNA as negative regulator, are gaining increasing recognition as key regulatory elements of cellular homeostasis. The ATP-gated purinergic P2X7 receptor (P2X7R) is an important driver of inflammation and has been implicated in the pathogenesis of numerous brain diseases including epilepsy. Changes in P2X7R expression have been reported in both experimental models and in epilepsy patients but the mechanism(s) controlling P2X7R levels remain incompletely understood. The specificity protein 1 (Sp1) has been shown to induce P2X7R transcription in vitro and recent data has identified microRNA-22 as a post-transcriptional repressor of P2X7R expression after seizures. In the present study we show that Sp1 can induce the transcription of both microRNA-22 and P2X7R in vitro during increased neuronal activity and in vivo in a mouse model of status epilepticus. We further show that Sp1-driven microRNA-22 transcription is calcium-sensitive and Sp1 occupancy of the microRNA-22 promoter region is blocked under conditions of seizure activity sufficient to elicit neuronal death. Taken together, our results suggest a neuronal activity-dependent P2X7R expression which is induced by the transcription factor Sp1 and repressed in a calcium-dependent manner by microRNA-22.

Evidence for evolutionary divergence of activity-dependent gene expression in developing neurons

Evolutionary differences in gene regulation between humans and lower mammalian experimental systems are incompletely understood, a potential translational obstacle that is challenging to surmount in neurons, where primary tissue availability is poor. Rodent-based studies show that activity-dependent transcriptional programs mediate myriad functions in neuronal development, but the extent of their conservation in human neurons is unknown. We compared activity-dependent transcriptional responses in developing human stem cell-derived cortical neurons with those induced in developing primary- or stem cell-derived mouse cortical neurons. While activity-dependent gene-responsiveness showed little dependence on developmental stage or origin (primary tissue vs. stem cell), notable species-dependent differences were observed. Moreover, differential species-specific gene ortholog regulation was recapitulated in aneuploid mouse neurons carrying human chromosome-21, implicating promoter/enhancer sequence divergence as a factor, including human-specific activity-responsive AP-1 sites. These findings support the use of human neuronal systems for probing transcriptional responses to physiological stimuli or indeed pharmaceutical agents.

Review : The Immediate-Early Gene Response and Neuronal Death and Regeneration

The induction of the cellular immediate-early gene (cIEG) response is the earliest known transcriptional con sequence of neuronal excitation. It is believed that the products of the cIEGs (such as c- fos and c- jun) serve to bring about persistent changes in neuronal phenotype by altering gene expression and modifying signal transduction pathways. This has led, on the one hand, to the burgeoning use of Fos immunohistochemistry as a surrogate form of neuronal activity mapping and, on the other hand, to a quest for the biochemical functions of individual cIEG products in the nervous system. Recent studies of neuronal death and regen eration have contributed substantially to our vision of the molecular and biological characteristics of the cIEG response. Indeed, they have challenged some of its long-held tenets. Therefore, we will use these results to illustrate our most contemporary view of the cIEG response in the nervous system. The Neuroscientist 1:68- 75,1995

REVIEW ■ : Regulation of Gene Expression by Neural Signals

Regulation of gene expression by extracellular signals is a ubiquitous biological mechanism controlling cell proliferation, differentiation, homeostasis, and adaptation to the environment. This article will focus on one set of issues within the broad topic of regulated gene expression: mechanisms by which neurotransmitters and neural activity regulate genes within the mature nervous system. The regulatory actions of growth factors, cytokines, and other types of extracellular signals are complex matters deserving separate review. This article proceeds from a basic overview of transcriptional regulation to a more specific discussion of the actions of two families of transcriptional regulators, the CREB family and the AP-1 family. These families of proteins are discussed because they play a central role in the regulation of gene expression by neurotransmitters and also because they exemplify many general principles of extracellular signal-regulated gene expression. NEUROSCIENTIST 2:217-224, 1996

Multiplexed Intact-Tissue Transcriptional Analysis at Cellular Resolution

In recently developed approaches for high-resolution imaging within intact tissue, molecular characterization over large volumes has been largely restricted to labeling of proteins. But volumetric nucleic acid labeling may represent a far greater scientific and clinical opportunity, enabling detection of not only diverse coding RNA variants but also non-coding RNAs. Moreover, scaling immunohistochemical detection to large tissue volumes has limitations due to high cost, limited renewability/availability, and restricted multiplexing capability of antibody labels. With the goal of versatile, high-content, and scalable molecular phenotyping of intact tissues, we developed a method using carbodiimide-based chemistry to stably retain RNAs in clarified tissue, coupled with amplification tools for multiplexed detection. The resulting technology enables robust measurement of activity-dependent transcriptional signatures, cell-identity markers, and diverse non-coding RNAs in rodent and human tissue volumes. The growing set of validated probes is deposited in an online resource for nucleating related developments from across the scientific community.

N-glycosylation in the hippocampus is required for the consolidation and reconsolidation of contextual fear memory

Memory consolidation and reconsolidation have been shown to require new gene expression. N-glycosylation, one of the major post-translational modifications, is known to play essential or regulatory roles in protein function. A previous study suggested that N-glycosylation is required for the maintenance of long-term potentiation in hippocampal CA1 neurons. However, the role of de novo N-glycosylation in learning and memory, such as memory consolidation and reconsolidation, still remains unclear. Here, we show critical roles for N-glycosylation in the consolidation and reconsolidation of contextual fear memory in mice. We examined the effects of pharmacological inhibition of N-glycosylation in the hippocampus on these memory processes using three different inhibitors (tunicamycin, 1-deoxynojirimycin, and swainsonine) that block the enzymatic activity required for N-glycosylation at different steps. Microinfusions of the N-glycosylation inhibitors into the dorsal hippocampus impaired long-term memory (LTM) formation without affecting short-term memory (STM). Similarly, this pharmacological blockade of N-glycosylation in the dorsal hippocampus also disrupted post-reactivation LTM after retrieval without affecting post-reactivation STM. Additionally, a microinfusion of swainsonine blocked c-fos induction in the hippocampus, which is observed when memory is consolidated. Our observations showed that N-glycosylation is required for the consolidation and reconsolidation of contextual fear memory and suggested that N-glycosylation contributes to the new gene expression necessary for these memory processes.

EXPRESS: Phospholipase C gamma mediates endogenous brain-derived neurotrophic factor - regulated calcitonin gene-related peptide expression in colitis - induced visceral pain

BACKGROUND

Visceral hypersensitivity is a complex pathophysiological paradigm with unclear mechanisms. Primary afferent neuronal plasticity marked by alterations in neuroactive compounds such as calcitonin gene-related peptide is suggested to underlie the heightened sensory responses. Signal transduction that leads to calcitonin gene-related peptide expression thereby sensory neuroplasticity during colitis remains to be elucidated.

RESULTS

In a rat model with colitis induced by 2,4,6-trinitrobenzene sulfonic acid, we found that endogenously elevated brain-derived neurotrophic factor elicited an up-regulation of calcitonin gene-related peptide in the lumbar L1 dorsal root ganglia. At seven days of colitis, neutralization of brain-derived neurotrophic factor with a specific brain-derived neurotrophic factor antibody reversed calcitonin gene-related peptide up-regulation in the dorsal root ganglia. Colitis-induced calcitonin gene-related peptide transcription was also inhibited by brain-derived neurotrophic factor antibody treatment. Signal transduction studies with dorsal root ganglia explants showed that brain-derived neurotrophic factor-induced calcitonin generelated peptide expression was mediated by the phospholipase C gamma, but not the phosphatidylinositol 3-kinase/Akt or the mitogen-activated protein kinase/extracellular signal-regulated protein kinase pathway. Application of PLC inhibitor U73122 in vivo confirmed that colitis-induced and brain-derived neurotrophic factor-mediated calcitonin gene-related peptide up-regulation in the dorsal root ganglia was regulated by the phospholipase C gamma pathway. In contrast, suppression of the phosphatidylinositol 3-kinase activity in vivo had no effect on colitis-induced calcitonin gene-related peptide expression. During colitis, calcitonin gene-related peptide also co-expressed with phospholipase C gamma but not with p-Akt. Calcitonin gene-related peptide up-regulation during colitis correlated to the activation of cAMP-responsive element binding protein in the same neurons. Consistently, colitis-induced cAMP-responsive element binding protein activation in the dorsal root ganglia was attenuated by brain-derived neurotrophic factor antibody treatment.

CONCLUSION

These results suggest that colitis-induced and brain-derived neurotrophic factor-mediated calcitonin generelated peptide expression in sensory activation is regulated by a unique pathway involving brain-derived neurotrophic factorphospholipase C gamma-cAMP-responsive element binding protein axis.

Englerin A Inhibits EWS-FLI1 DNA Binding in Ewing Sarcoma Cells

High-throughput screening of extracts from plants, marine, and micro-organisms led to the identification of the extract from the plant Phyllanthus engleri as the most potent inhibitor of EWS-FLI1 induced luciferase reporter expression. Testing of compounds isolated from this extract in turn led to the identification of Englerin A (EA) as the active constituent of the extract. EA induced both necrosis and apoptosis in Ewing cells subsequent to a G2M accumulation of cells in the cell cycle. It also impacted clonogenic survival and anchorage-independent proliferation while also decreasing the proportion of chemotherapy-resistant cells identified by high ALDH activity. EA also caused a sustained increase in cytosolic calcium levels. EA appears to exert its effect on Ewing cells through a decrease in phosphorylation of EWS-FLI1 and its ability to bind DNA. This effect is mediated, at least in part, through a decrease in the levels of the calcium-dependent protein kinase PKC-βI after a transient up-regulation.

Nuclear RNA-seq of single neurons reveals molecular signatures of activation

Single-cell sequencing methods have emerged as powerful tools for identification of heterogeneous cell types within defined brain regions. Application of single-cell techniques to study the transcriptome of activated neurons can offer insight into molecular dynamics associated with differential neuronal responses to a given experience. Through evaluation of common whole-cell and single-nuclei RNA-sequencing (snRNA-seq) methods, here we show that snRNA-seq faithfully recapitulates transcriptional patterns associated with experience-driven induction of activity, including immediate early genes (IEGs) such as Fos, Arc and Egr1. SnRNA-seq of mouse dentate granule cells reveals large-scale changes in the activated neuronal transcriptome after brief novel environment exposure, including induction of MAPK pathway genes. In addition, we observe a continuum of activation states, revealing a pseudotemporal pattern of activation from gene expression alone. In summary, snRNA-seq of activated neurons enables the examination of gene expression beyond IEGs, allowing for novel insights into neuronal activation patterns in vivo.

The molecular dynamics associated with neuronal activation patterns in vivo are unclear. Lacar et al. perform single-nuclei RNA-sequencing of hippocampal neurons from mice exposed to a novel environment, and identify large-scale transcriptome changes in individual neurons associated with the experience.

Calcium-dependent Nr4a1 expression in mouse Leydig cells requires distinct AP1/CRE and MEF2 elements

The nuclear receptor NR4A1 is expressed in steroidogenic Leydig cells where it plays pivotal roles by regulating the expression of several genes involved in steroidogenesis and male sex differentiation including Star, HSD3B2, and Insl3 Activation of the cAMP and Ca(2+) signaling pathways in response to LH stimulation leads to a rapid and robust activation of Nr4a1 gene expression that requires the Ca(2+)/CAMKI pathway. However, the downstream transcription factor(s) have yet to be characterized. To identify potential Ca(2+)/CaM effectors responsible for hormone-induced Nr4a1 expression, MA-10 Leydig cells were treated with forskolin to increase endogenous cAMP levels, dantrolene to inhibit endoplasmic reticulum Ca(2+) release, and W7 to inhibit CaM activity. We identified Ca(2+)-responsive elements located in the discrete regions of the Nr4a1 promoter, which contain binding sites for several transcription factors such as AP1, CREB, and MEF2. We found that one of the three AP1/CRE sites located at -255 bp is the most responsive to the Ca(2+) signaling pathway as are the two MEF2 binding sites at -315 and -285 bp. Furthermore, we found that the hormone-induced recruitment of phospho-CREB and of the co-activator p300 to the Nr4a1 promoter requires the Ca(2+) pathway. Lastly, siRNA-mediated knockdown of CREB impaired NR4A1 expression and steroidogenesis. Together, our data indicate that the Ca(2+) signaling pathway increases Nr4a1 expression in MA-10 Leydig cells, at least in part, by enhancing the recruitment of coactivator most likely through the MEF2, AP1, and CREB transcription factors thus demonstrating an important interplay between the Ca(2+) and cAMP pathways in regulating Nr4a1 expression.

Neuronal activity controls Bdnf expression via Polycomb de-repression and CREB/CBP/JMJD3 activation in mature neurons

It has been recently described that in embryonic stem cells, the expression of some important developmentally regulated genes is repressed, but poised for fast activation under the appropriate stimuli. In this work we show that Bdnf promoters are repressed by Polycomb Complex 2 in mature hippocampal neurons, and basal expression is guaranteed by the coexistence with activating histone marks. Neuronal stimulation triggered by N-methyl-D-aspartate application induces the transcription of these promoters by H3K27Me3 demethylation and H3K27Me3 phosphorylation at Serine 28 leading to displacement of EZH2, the catalytic subunit of Polycomb Repressor Complex 2. Our data show that the fast transient expression of Bdnf promoters II and VI after neuronal stimulation is dependent on acetylation of histone H3K27 by CREB-p/CBP. Thus, regulatory mechanisms established during development seem to remain after differentiation controlling genes induced by different stimuli, as would be the case of early memory genes in mature neurons.

In neurons, brain-derived neurotrophic factor (BDNF) transcription is activated by synaptic activity, in part by epigenetic regulation of its promoter regions. Here the authors characterize histone modifications in response to NMDA treatment that result in different kinetics of Bdnf activation from its different promoter regions.

Knowledge About Sounds-Context-Specific Meaning Differently Activates Cortical Hemispheres, Auditory Cortical Fields, and Layers in House Mice

Activation of the auditory cortex (AC) by a given sound pattern is plastic, depending, in largely unknown ways, on the physiological state and the behavioral context of the receiving animal and on the receiver's experience with the sounds. Such plasticity can be inferred when house mouse mothers respond maternally to pup ultrasounds right after parturition and naïve females have to learn to respond. Here we use c-FOS immunocytochemistry to quantify highly activated neurons in the AC fields and layers of seven groups of mothers and naïve females who have different knowledge about and are differently motivated to respond to acoustic models of pup ultrasounds of different behavioral significance. Profiles of FOS-positive cells in the AC primary fields (AI, AAF), the ultrasonic field (UF), the secondary field (AII), and the dorsoposterior field (DP) suggest that activation reflects in AI, AAF, and UF the integration of sound properties with animal state-dependent factors, in the higher-order field AII the news value of a given sound in the behavioral context, and in the higher-order field DP the level of maternal motivation and, by left-hemisphere activation advantage, the recognition of the meaning of sounds in the given context. Anesthesia reduced activation in all fields, especially in cortical layers 2/3. Thus, plasticity in the AC is field-specific preparing different output of AC fields in the process of perception, recognition and responding to communication sounds. Further, the activation profiles of the auditory cortical fields suggest the differentiation between brains hormonally primed to know (mothers) and brains which acquired knowledge via implicit learning (naïve females). In this way, auditory cortical activation discriminates between instinctive (mothers) and learned (naïve females) cognition.

An Emerging Technology Framework for the Neurobiology of Appetite

Advances in neuro-technology for mapping, manipulating, and monitoring molecularly defined cell types are rapidly advancing insight into neural circuits that regulate appetite. Here, we review these important tools and their applications in circuits that control food seeking and consumption. Technical capabilities provided by these tools establish a rigorous experimental framework for research into the neurobiology of hunger.

Expression of mRNA Encoding Mcu and Other Mitochondrial Calcium Regulatory Genes Depends on Cell Type, Neuronal Subtype, and Ca2+ Signaling

Uptake of Ca²⁺ into the mitochondrial matrix controls cellular metabolism and survival-death pathways. Several genes are implicated in controlling mitochondrial Ca²⁺ uptake (mitochondrial calcium regulatory genes, MCRGs), however, less is known about the factors which influence their expression level. Here we have compared MCRG mRNA expression, in neural cells of differing type (cortical neurons vs. astrocytes), differing neuronal subtype (CA3 vs. CA1 hippocampus) and in response to Ca²⁺ influx, using a combination of qPCR and RNA-seq analysis. Of note, we find that the Mcu-regulating Micu gene family profile differs substantially between neurons and astrocytes, while expression of Mcu itself is markedly different between CA3 and CA1 regions in the adult hippocampus. Moreover, dynamic control of MCRG mRNA expression in response to membrane depolarization-induced Ca²⁺ influx is also apparent, resulting in repression of Letm1, as well as Mcu. Thus, the mRNA expression profile of MCRGs is not fixed, which may cause differences in the coupling between cytoplasmic and mitochondrial Ca²⁺, as well as diversity of mitochondrial Ca²⁺ uptake mechanisms.

CREB, AP-1, ternary complex factors and MAP kinases connect transient receptor potential melastatin-3 (TRPM3) channel stimulation with increased c-Fos expression

BACKGROUND AND PURPOSE

The rise in intracellular Ca(2+) stimulates the expression of the transcription factor c-Fos. Depending on the mode of entry of Ca(2+) into the cytosol, distinct signal transducers and transcription factors are required. Here, we have analysed the signalling pathway connecting a Ca(2+) influx via activation of transient receptor potential melastatin-3 (TRPM3) channels with enhanced c-Fos expression.

EXPERIMENTAL APPROACH

Transcription of c-Fos promoter/reporter genes that were integrated into the chromatin via lentiviral gene transfer was analysed in HEK293 cells overexpressing TRPM3. The transcriptional activation potential of c-Fos was measured using a GAL4-c-Fos fusion protein.

KEY RESULTS

The signalling pathway connecting TRPM3 stimulation with enhanced c-Fos expression requires the activation of MAP kinases. On the transcriptional level, three Ca(2+) -responsive elements, the cAMP-response element and the binding sites for the serum response factor (SRF) and AP-1, are essential for the TRPM3-mediated stimulation of the c-Fos promoter. Ternary complex factors are additionally involved in connecting TRPM3 stimulation with the up-regulation of c-Fos expression. Stimulation of TRPM3 channels also increases the transcriptional activation potential of c-Fos.

CONCLUSIONS AND IMPLICATIONS

Signalling molecules involved in connecting TRPM3 with the c-Fos gene are MAP kinases and the transcription factors CREB, SRF, AP-1 and ternary complex factors. As c-Fos constitutes, together with other basic region leucine zipper transcription factors, the AP-1 transcription factor complex, the results of this study explain TRPM3-induced activation of AP-1 and connects TRPM3 with the biological functions regulated by AP-1.

Thapsigargin-induced activation of Ca(2+)-CaMKII-ERK in brainstem contributes to substance P release and induction of emesis in the least shrew

Cytoplasmic calcium (Ca(2+)) mobilization has been proposed to be an important factor in the induction of emesis. The selective sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase (SERCA) inhibitor thapsigargin, is known to deplete intracellular Ca(2+) stores, which consequently evokes extracellular Ca(2+) entry through cell membrane-associated channels, accompanied by a prominent rise in cytosolic Ca(2+). A pro-drug form of thapsigargin is currently under clinical trial as a targeted cancer chemotherapeutic. We envisioned that the intracellular effects of thapsigargin could cause emesis and planned to investigate its mechanisms of emetic action. Indeed, thapsigargin did induce vomiting in the least shrew in a dose-dependent and bell-shaped manner, with maximal efficacy (100%) at 0.5 mg/kg (i.p.). Thapsigargin (0.5 mg/kg) also caused increases in c-Fos immunoreactivity in the brainstem emetic nuclei including the area postrema (AP), nucleus tractus solitarius (NTS) and dorsal motor nucleus of the vagus (DMNX), as well as enhancement of substance P (SP) immunoreactivity in DMNX. In addition, thapsigargin (0.5 mg/kg, i.p.) led to vomit-associated and time-dependent increases in phosphorylation of Ca(2+)/calmodulin kinase IIα (CaMKIIα) and extracellular signal-regulated protein kinase 1/2 (ERK1/2) in the brainstem. We then explored the suppressive potential of diverse chemicals against thapsigargin-evoked emesis including antagonists of: i) neurokinin-1 receptors (netupitant), ii) the type 3 serotonin receptors (palonosetron), iii) store-operated Ca(2+) entry (YM-58483), iv) L-type Ca(2+) channels (nifedipine), and v) SER Ca(2+)-release channels inositol trisphosphate (IP3Rs) (2-APB)-, and ryanodine (RyRs) (dantrolene)-receptors. In addition, the antiemetic potential of inhibitors of CaMKII (KN93) and ERK1/2 (PD98059) were investigated. All tested antagonists/blockers attenuated emetic parameters to varying degrees except palonosetron, however a combination of non-effective doses of netupitant and palonosetron exhibited additive antiemetic efficacy. A low-dose combination of nifedipine and 2-APB plus dantrolene mixture completely abolished thapsigargin-evoked vomiting, CaMKII-ERK1/2 activation and SP elevation. In addition, pretreatment with KN93 or PD98059 suppressed thapsigargin-induced increases in SP and ERK1/2 activation. Intracerebroventricular injection of netupitant suppressed vomiting caused by thapsigargin which suggests that the principal site of evoked emesis is the brainstem. In sum, this is the first study to demonstrate that thapsigargin causes vomiting via the activation of the Ca(2+)-CaMKII-ERK1/2 cascade, which is associated with an increase in the brainstem tissue content of SP, and the evoked emesis occurs through SP-induced activation of neurokinin-1 receptors.

Effects of the Concomitant Activation of ON and OFF Retinal Ganglion Cells on the Visual Thalamus: Evidence for an Enhanced Recruitment of GABAergic Cells

A fundamental question in vision neuroscience is how parallel processing of Retinal Ganglion Cell (RGC) signals is integrated at the level of the visual thalamus. It is well-known that parallel ON-OFF pathways generate output signals from the retina that are conveyed to the dorsal lateral geniculate nucleus (dLGN). However, it is unclear how these signals distribute onto thalamic cells and how these two pathways interact. Here, by electrophysiological recordings and c-Fos expression analysis, we characterized the effects of pharmacological manipulations of the retinal circuit aimed at inducing either a selective activation of a single pathway, OFF RGCs [intravitreal L-(+)-2-Amino-4-phosphonobutyric, L-AP4] or an unregulated activity of all classes of RGCs (intravitreal 4-Aminopyridine, 4-AP). In in vivo experiments, the analysis of c-Fos expression in the dLGN showed that these two manipulations recruited active cells from the same area, the lateral edge of the dLGN. Despite this similarity, the unregulated co-activation of both ON and OFF pathways by 4-AP yielded a much stronger recruitment of GABAergic interneurons in the dLGN when compared to L-AP4 pure OFF activation. The increased activation of an inhibitory thalamic network by a high level of unregulated discharge of ON and OFF RGCs might suggest that cross-inhibitory pathways between opposing visual channels are presumably replicated at multiple levels in the visual pathway, thus increasing the filtering ability for non-informative or noisy visual signals.

Convergent effects of Ca(2+) and cAMP signals on the expression of immediate early genes in neurons

How the expression of immediate early genes (IEGs) is controlled in response to neurotransmissions is unknown. Using cultured rat cortical cells, we investigated the expression of IEGs regulated by Ca(2+) and/or cAMP signals. The expression of c-fos was transiently induced by treatment of cells with high potassium (high K(+)), which evoked depolarization, or forskolin, an adenylate cyclase activator. c-fos expression was persistently and synergistically induced by simultaneous treatment with high K(+) and forskolin via cAMP-response element (CRE). Microarray analysis indicated the expression profiles of IEGs caused by depolarization in the presence or absence of forskolin. When a novel index was included to investigate the profile of IEGs, we found that high K(+)-induced expression of IEGs was stimulatory or negatively changed in the presence of forskolin, suggesting distinct convergent effects of Ca(2+) and cAMP signals on the expression of IEGs.

Transcription factors FOXA1 and FOXA2 maintain dopaminergic neuronal properties and control feeding behavior in adult mice

Midbrain dopaminergic (mDA) neurons are implicated in cognitive functions, neuropsychiatric disorders, and pathological conditions; hence understanding genes regulating their homeostasis has medical relevance. Transcription factors FOXA1 and FOXA2 (FOXA1/2) are key determinants of mDA neuronal identity during development, but their roles in adult mDA neurons are unknown. We used a conditional knockout strategy to specifically ablate FOXA1/2 in mDA neurons of adult mice. We show that deletion of Foxa1/2 results in down-regulation of tyrosine hydroxylase, the rate-limiting enzyme of dopamine (DA) biosynthesis, specifically in dopaminergic neurons of the substantia nigra pars compacta (SNc). In addition, DA synthesis and striatal DA transmission were reduced after Foxa1/2 deletion. Furthermore, the burst-firing activity characteristic of SNc mDA neurons was drastically reduced in the absence of FOXA1/2. These molecular and functional alterations lead to a severe feeding deficit in adult Foxa1/2 mutant mice, independently of motor control, which could be rescued by L-DOPA treatment. FOXA1/2 therefore control the maintenance of molecular and physiological properties of SNc mDA neurons and impact on feeding behavior in adult mice.

Evolutionary and functional perspectives on signaling from neuronal surface to nucleus

Reliance on Ca(2+) signaling has been well-preserved through the course of evolution. While the complexity of Ca(2+) signaling pathways has increased, activation of transcription factors including CREB by Ca(2+)/CaM-dependent kinases (CaMKs) has remained critical for long-term plasticity. In C. elegans, the CaMK family is made up of only three members, and CREB phosphorylation is mediated by CMK-1, the homologue of CaMKI. CMK-1 nuclear translocation directly regulates adaptation of thermotaxis behavior in response to changes in the environment. In mammals, the CaMK family has been expanded from three to ten members, enabling specialization of individual elements of a signal transduction pathway and increased reliance on the CaMKII subfamily. This increased complexity enables private line communication between Ca(2+) sources at the cell surface and specific cellular targets. Using both new and previously published data, we review the mechanism of a γCaMKII-CaM nuclear translocation. This intricate pathway depends on a specific role for multiple Ca(2+)/CaM-dependent kinases and phosphatases: α/βCaMKII phosphorylates γCaMKII to trap CaM; CaN dephosphorylates γCaMKII to dispatch it to the nucleus; and PP2A induces CaM release from γCaMKII so that CaMKK and CaMKIV can trigger CREB phosphorylation. Thus, while certain basic elements have been conserved from C. elegans, evolutionary modifications offer opportunities for targeted communication, regulation of key nodes and checkpoints, and greater specificity and flexibility in signaling.

Emergence of spatial behavioral function and associated mossy fiber connectivity and c-Fos labeling patterns in the hippocampus of rats

Improvement on spatial tasks is observed during a late, postnatal developmental period (PND18 – PND24).  The purpose of the current work was 1) to determine whether the emergence of spatial-behavioral function was based on the ability to generate appropriate behavioral output; 2) to assess whether mossy fiber connectivity patterns preceded the emergence of spatial-behavioral function; 3) to explore functional changes in the hippocampus to determine whether activity in hippocampal networks occurred in a training-dependent or developmentally-dependent fashion.  To these ends, male, Long Evans rats were trained on a spatial water or dry maze task for one day (PND16, PND18 or PND20) then euthanized.  Training on these 2 tasks with opposing behavioral demands (swimming versus exploration) was hypothesized to control for behavioral topology.  Only at PND20 was there evidence of spatial-behavioral function for both tasks.  Examination of synaptophysin staining in the CA3 region (i.e., mossy fiber projections) revealed enhanced connectivity patterns that preceded the emergence of spatial behavior.  Analysis of c-Fos labeling (functional changes) revealed developmentally-dependent increases in c-Fos positive cells in the dentate gyrus, CA3 and CA1 regions whereas training-dependent increases were noted in the CA3 and CA1 regions for the water-maze trained groups.  Results suggest that changes in mossy fiber connectivity in association with enhanced hippocampal functioning precede the emergence of spatial behavior observed at PND20.  The combination of neuroanatomical and behavioural results confirms the hypothesis that this time represents a sensitive period for hippocampal development and modification and the emergence of spatial/ cognitive function.

LRP8-Reelin-Regulated Neuronal Enhancer Signature Underlying Learning and Memory Formation

One of the exceptional properties of the brain is its ability to acquire new knowledge through learning and to store that information through memory. The epigenetic mechanisms linking changes in neuronal transcriptional programs to behavioral plasticity remain largely unknown. Here, we identify the epigenetic signature of the neuronal enhancers required for transcriptional regulation of synaptic plasticity genes during memory formation, linking this to Reelin signaling. The binding of Reelin to its receptor, LRP8, triggers activation of this cohort of LRP8-Reelin-regulated neuronal (LRN) enhancers that serve as the ultimate convergence point of a novel synapse-to-nucleus pathway. Reelin simultaneously regulates NMDA-receptor transmission, which reciprocally permits the required γ-secretase-dependent cleavage of LRP8, revealing an unprecedented role for its intracellular domain in the regulation of synaptically generated signals. These results uncover an in vivo enhancer code serving as a critical molecular component of cognition and relevant to psychiatric disorders linked to defects in Reelin signaling.

Sex differences in feeding behavior in rats: the relationship with neuronal activation in the hypothalamus

There is general agreement that the central nervous system in rodents differs between sexes due to the presence of gonadal steroid hormone during differentiation. Sex differences in feeding seem to occur among species, and responses to fasting (i.e., starvation), gonadal steroids (i.e., testosterone and estradiol), and diet (i.e., western-style diet) vary significantly between sexes. The hypothalamus is the center for controlling feeding behavior. We examined the activation of feeding-related peptides in neurons in the hypothalamus. Phosphorylation of cyclic AMP response element-binding protein (CREB) is a good marker for neural activation, as is the Fos antigen. Therefore, we predicted that sex differences in the activity of melanin-concentrating hormone (MCH) neurons would be associated with feeding behavior. We determined the response of MCH neurons to glucose in the lateral hypothalamic area (LHA) and our results suggested MCH neurons play an important role in sex differences in feeding behavior. In addition, fasting increased the number of orexin neurons harboring phosphorylated CREB in female rats (regardless of the estrous day), but not male rats. Glucose injection decreased the number of these neurons with phosphorylated CREB in fasted female rats. Finally, under normal spontaneous food intake, MCH neurons, but not orexin neurons, expressed phosphorylated CREB. These sex differences in response to fasting and glucose, as well as under normal conditions, suggest a vulnerability to metabolic challenges in females.

γCaMKII shuttles Ca²⁺/CaM to the nucleus to trigger CREB phosphorylation and gene expression

Activity-dependent CREB phosphorylation and gene expression are critical for long-term neuronal plasticity. Local signaling at CaV1 channels triggers these events, but how information is relayed onward to the nucleus remains unclear. Here, we report a mechanism that mediates long-distance communication within cells: a shuttle that transports Ca(2+)/calmodulin from the surface membrane to the nucleus. We show that the shuttle protein is γCaMKII, its phosphorylation at Thr287 by βCaMKII protects the Ca(2+)/CaM signal, and CaN triggers its nuclear translocation. Both βCaMKII and CaN act in close proximity to CaV1 channels, supporting their dominance, whereas γCaMKII operates as a carrier, not as a kinase. Upon arrival within the nucleus, Ca(2+)/CaM activates CaMKK and its substrate CaMKIV, the CREB kinase. This mechanism resolves long-standing puzzles about CaM/CaMK-dependent signaling to the nucleus. The significance of the mechanism is emphasized by dysregulation of CaV1, γCaMKII, βCaMKII, and CaN in multiple neuropsychiatric disorders.

Ca2+ signals regulate mitochondrial metabolism by stimulating CREB-mediated expression of the mitochondrial Ca2+ uniporter gene MCU

Cytosolic Ca2+ signals, generated through the coordinated translocation of Ca2+ across the plasma membrane (PM) and endoplasmic reticulum (ER) membrane, mediate diverse cellular responses. Mitochondrial Ca2+ is important for mitochondrial function, and when cytosolic Ca2+ concentration becomes too high, mitochondria function as cellular Ca2+ sinks. By measuring mitochondrial Ca2+ currents, we found that mitochondrial Ca2+ uptake was reduced in chicken DT40 B lymphocytes lacking either the ER-localized inositol trisphosphate receptor (IP3R), which releases Ca2+ from the ER, or Orai1 or STIM1, components of the PM-localized Ca2+ -permeable channel complex that mediates store-operated calcium entry (SOCE) in response to depletion of ER Ca2+ stores. The abundance of MCU, the pore-forming subunit of the mitochondrial Ca2+ uniporter, was reduced in cells deficient in IP3R, STIM1, or Orai1. Chromatin immunoprecipitation and promoter reporter analyses revealed that the Ca2+ -regulated transcription factor CREB (cyclic adenosine monophosphate response element-binding protein) directly bound the MCU promoter and stimulated expression. Lymphocytes deficient in IP3R, STIM1, or Orai1 exhibited altered mitochondrial metabolism, indicating that Ca2+ released from the ER and SOCE-mediated signals modulates mitochondrial function. Thus, our results showed that a transcriptional regulatory circuit involving Ca2+ -dependent activation of CREB controls the Ca2+ uptake capability of mitochondria and hence regulates mitochondrial metabolism.

Hippocampal dysfunctions caused by cranial irradiation: a review of the experimental evidence

Cranial irradiation (IR) is commonly used for the treatment of brain tumors but may cause disastrous brain injury, especially in the hippocampus, which has important cognition and emotional regulation functions. Several preclinical studies have investigated the mechanisms associated with cranial IR-induced hippocampal dysfunction such as memory defects and depression-like behavior. However, current research on hippocampal dysfunction and its associated mechanisms, with the ultimate goal of overcoming the side effects of cranial radiation therapy in the hippocampus, is still very much in progress. This article reviews several in vivo studies on the possible mechanisms of radiation-induced hippocampal dysfunction, which may be associated with hippocampal neurogenesis, neurotrophin and neuroinflammation. Thus, this review may be helpful to gain new mechanistic insights into hippocampal dysfunction following cranial IR and provide effective strategies for potential therapeutic approaches for cancer patients receiving radiation therapy.

Histone acetylation of the htr3a gene in the prefrontal cortex of Wistar rats regulates ethanol-seeking behavior

Previous reports showed that decreased histone deacetylase activity significantly potentiated the rewarding effects of psychostimulants, and that encoding of the 5-HT3 receptor by the htr3a gene was related to ethanol-seeking behavior. However, the effects of a histone deacetylase inhibitor on ethanol-seeking behavior and epigenetic regulation of htr3a mRNA expression after chronic ethanol exposure are not fully understood. Using quantitative reverse transcription-polymerase chain reaction and chromatin immunoprecipitation analysis, we investigated the effects of chronic ethanol exposure and its interaction with a histone deacetylase inhibitor on histone-acetylation-mediated changes in htr3a mRNA expression in the htr3a promoter region. The conditioned place preference procedure was used to evaluate ethanol-seeking behavior. Chronic exposure to ethanol effectively elicited place conditioning. In the prefrontal cortex, the acetylation of H3K9 and htr3a mRNA expression in the htr3a promoter region were significantly higher in the ethanol group than in the saline group. The histone deacetylase inhibitor sodium butyrate potentiated the effects of ethanol on htr3a mRNA expression and enhanced ethanol-induced conditioned place preferences. These results suggest that ethanol upregulates htr3a levels through mechanisms involving H3K9 acetylation, and that histone acetylation may be a therapeutic target for treating ethanol abuse.