Synaptogenesis regulates axotomy-induced activation of c-Jun-activator protein-1 transcription

Involvement of JNK1 in Neuronal Polarization During Brain Development

The c-Jun N-terminal Kinases (JNKs) are a group of regulatory elements responsible for the control of a wide array of functions within the cell. In the central nervous system (CNS), JNKs are involved in neuronal polarization, starting from the cell division of neural stem cells and ending with their final positioning when migrating and maturing. This review will focus mostly on isoform JNK1, the foremost contributor of total JNK activity in the CNS. Throughout the text, research from multiple groups will be summarized and discussed in order to describe the involvement of the JNKs in the different steps of neuronal polarization. The data presented support the idea that isoform JNK1 is highly relevant to the regulation of many of the processes that occur in neuronal development in the CNS.

Immediate-Early Genes Detection in the CNS of Terrestrial Snail

In the present work, using in situ hybridization, we studied the expression patterns of three molluscan homologs of vertebrate immediate-early genes C/EBP, c-Fos, and c-Jun in the central nervous system (CNS) of terrestrial gastropod snail Helix. The molluscan C/EBP gene was described in literature, while c-Fos and c-Jun were studied in terrestrial snails for the first time. Localization of the expression was traced in normal conditions, and in preparations physiologically activated using stimulation of suboesophageal ganglia nerves. No expression was detected constitutively. In stimulated preparations, all three genes had individual expression patterns in Helix CNS, and the level of expression was stimulus-dependent. The number of cells expressing the gene of interest was different from the number of cells projecting to the stimulated nerve, and thus activated retrogradely. This difference depended on the ganglia studied. At the subcellular level, the labeled RNA was observed as dots (probably small clusters of RNA molecules) and shapeless mass of RNA, often seen as a circle at the internal border of the cell nuclei. The data provide a basis for further study of behavioral role of these putative immediate-early genes in snail behavior and learning.

Identification of Immediate Early Genes in the Nervous System of Snail Helix lucorum

Immediate early genes (IEGs) are useful markers of neuronal activation and essential components of neuronal response. While studies of gastropods have provided many insights into the basic learning and memory mechanisms, the genome-wide assessment of IEGs has been mainly restricted to vertebrates. In this study, we identified IEGs in the terrestrial snail Helix lucorum In the absence of the genome, we conducted de novo transcriptome assembly using reads with short and intermediate lengths cumulatively covering more than 98 billion nucleotides. Based on this assembly, we identified 37 proteins corresponding to contigs differentially expressed (DE) in either the parietal ganglia (PaG) or two giant interneurons located within the PaG of the snail in response to the neuronal stimulation. These proteins included homologues of well-known mammalian IEGs, such as c-jun/jund, C/EBP, c-fos/fosl2, and Egr1, as well as homologues of genes not yet implicated in the neuronal response.

General Anesthesia and Young Brain: What is New?

Considering that growing population of very young children is exposed to general anesthesia every year, it is of utmost importance to understand how and whether such practice may affect the development and growth of their very immature and vulnerable brains. Compelling evidence from animal studies suggests that an early exposure to general anesthesia is detrimental to normal brain development leading to structural and functional impairments of neurons and glia, and long-lasting impairments in normal emotional and cognitive development. Although the evidence from animal studies is overwhelming and confirmed across species examined from rodents to non-human primates, the evidence from human studies is inconsistent and not conclusive at present. In this review we focus on new developments in animal studies of anesthesia-induced developmental neurotoxicity and summarize recent clinical studies while focusing on outcome measures and exposure variables in terms of their utility for assessing cognitive and behavioral development in children.

General Anesthesia Causes Epigenetic Histone Modulation of c-Fos and Brain-derived Neurotrophic Factor, Target Genes Important for Neuronal Development in the Immature Rat Hippocampus

BACKGROUND

Early postnatal exposure to general anesthesia (GA) may be detrimental to brain development, resulting in long-term cognitive impairments. Older literature suggests that in utero exposure of rodents to GA causes cognitive impairments in the first-generation as well as in the second-generation offspring never exposed to GA. Thus, the authors hypothesize that transient exposure to GA during critical stages of synaptogenesis causes epigenetic changes in chromatin with deleterious effects on transcription of target genes crucial for proper synapse formation and cognitive development. They focus on the effects of GA on histone acetyltransferase activity of cAMP-responsive element-binding protein and the histone-3 acetylation status in the promoters of the target genes brain-derived neurotrophic factor and cellular Finkel-Biskis-Jinkins murine sarcoma virus osteosarcoma oncogene (c-Fos) known to regulate the development of neuronal morphology and function.

METHODS

Seven-day-old rat pups were exposed to a sedative dose of midazolam followed by combined nitrous oxide and isoflurane anesthesia for 6 h. Hippocampal neurons and organotypic hippocampal slices were cultured in vitro and exposed to GA for 24 h.

RESULTS

GA caused epigenetic modulations manifested as histone-3 hypoacetylation (decrease of 25 to 30%, n = 7 to 9) and fragmentation of cAMP-responsive element-binding protein (two-fold increase, n = 6) with 25% decrease in its histone acetyltransferase activity, which resulted in down-regulated transcription of brain-derived neurotrophic factor (0.2- to 0.4-fold, n = 7 to 8) and cellular Finkel-Biskis-Jinkins murine sarcoma virus osteosarcoma oncogene (about 0.2-fold, n = 10 to 12). Reversal of histone hypoacetylation with sodium butyrate blocked GA-induced morphological and functional impairments of neuronal development and synaptic communication.

CONCLUSION

Long-term impairments of neuronal development and synaptic communication could be caused by GA-induced epigenetic phenomena.

A novel inhibitor of active protein kinase G attenuates chronic inflammatory and osteoarthritic pain

Supplemental Digital Content is Available in the Text.

A novel and potent protein kinase G-1α (PKG-1α) inhibitor is used to demonstrate the important roles of PKG in capsaicin-induced acute pain and in persistent inflammatory pain.

Activating PKG-1α induces a long-term hyperexcitability (LTH) in nociceptive neurons. Since the LTH correlates directly with chronic pain in many animal models, we tested the hypothesis that inhibiting PKG-1α would attenuate LTH-mediated pain. We first synthesized and characterized compound N46 (N-((3R,4R)-4-(4-(2-fluoro-3-methoxy-6-propoxybenzoyl)benzamido)pyrrolidin-3-yl)-1H-indazole-5-carboxamide). N46 inhibits PKG-1α with an IC₅₀ of 7.5 nmol, was highly selective when tested against a panel of 274 kinases, and tissue distribution studies indicate that it does not enter the CNS. To evaluate its antinociceptive potential, we used 2 animal models in which the pain involves both activated PKG-1α and LTH. Injecting complete Freund's adjuvant (CFA) into the rat hind paw causes a thermal hyperalgesia that was significantly attenuated 24 hours after a single intravenous injection of N46. Next, we used a rat model of osteoarthritic knee joint pain and found that a single intra-articular injection of N46 alleviated the pain 14 days after the pain was established and the relief lasted for 7 days. Thermal hyperalgesia and osteoarthritic pain are also associated with the activation of the capsaicin-activated transient receptor protein vanilloid-1 (TRPV1) channel. We show that capsaicin activates PKG-1α in nerves and that a subcutaneous delivery of N46 attenuated the mechanical and thermal hypersensitivity elicited by exposure to capsaicin. Thus, PKG-1α appears to be downstream of the transient receptor protein vanilloid-1. Our studies provide proof of concept in animal models that a PKG-1α antagonist has a powerful antinociceptive effect on persistent, already existing inflammatory pain. They further suggest that N46 is a valid chemotype for the further development of such antagonists.

cJun and CREB2 in the postsynaptic neuron contribute to persistent long-term facilitation at a behaviorally relevant synapse

Basic region leucine zipper (bZIP) transcription factors regulate gene expression critical for long-term synaptic plasticity or neuronal excitability contributing to learning and memory. At sensorimotor synapses of Aplysia, changes in activation or expression of CREB1 and CREB2 in sensory neurons are required for long-term synaptic plasticity. However, it is unknown whether concomitant stimulus-induced changes in expression and activation of bZIP transcription factors in the postsynaptic motor neuron also contribute to persistent long-term facilitation (P-LTF). We overexpressed various forms of CREB1, CREB2, or cJun in the postsynaptic motor neuron L7 in cell culture to examine whether these factors contribute to P-LTF. P-LTF is evoked by 2 consecutive days of 5-HT applications (2 5-HT), while a transient form of LTF is produced by 1 day of 5-HT applications (1 5-HT). Significant increases in the expression of both cJun and CREB2 mRNA in L7 accompany P-LTF. Overexpressing each bZIP factor in L7 did not alter basal synapse strength, while coexpressing cJun and CREB2 in L7 evoked persistent increases in basal synapse strength. In contrast, overexpressing cJun and CREB2 in sensory neurons evoked persistent decreases in basal synapse strength. Overexpressing wild-type cJun or CREB2, but not CREB1, in L7 can replace the second day of 5-HT applications in producing P-LTF. Reducing cJun activity in L7 blocked P-LTF evoked by 2 5-HT. These results suggest that expression and activation of different bZIP factors in both presynaptic and postsynaptic neurons contribute to persistent change in synapse strength including stimulus-dependent long-term synaptic plasticity.

The F-box protein Fbw7 is required for cerebellar development

The F-box protein Fbw7 (also known as Fbxw7, hCdc4 and Sel-10) functions as a substrate recognition component of a SCF-type E3 ubiquitin ligase. SCF(Fbw7) facilitates polyubiquitination and subsequent degradation of various proteins such as Notch, cyclin E, c-Myc and c-Jun. Fbw7 is highly expressed in the nervous system and controls neural stem cell differentiation and apoptosis via Notch and c-Jun during embryonic development (Hoeck et al., 2010). Fbw7 deletion in the neural lineage is perinatal lethal and thus prohibits studying the role of Fbw7 in the adult nervous system. fbw7 mRNA is highly expressed in the postnatal brain and to gain insights into the function of Fbw7 in postnatal neurogenesis we analysed Fbw7 function in the cerebellum. We generated conditional Fbw7-knockout mice (fbw7(∆Cb)) by inactivating Fbw7 specifically in the cerebellar anlage. This resulted in decreased cerebellar size, reduced Purkinje cell number and defects in axonal arborisation. Moreover, Fbw7-deficient cerebella showed supranumeral fissures and aberrant progenitor cell migration. Protein levels of the Fbw7 substrates Notch1 and N-terminally phosphorylated c-Jun were upregulated in fbw7(∆Cb) mice. Concomitant deletion of c-Jun, and also the junAA knock-in mutation which specifically abrogates c-Jun N-terminal phosphorylation, rescued Purkinje cell numbers and arborisation in the fbw7(∆Cb) background. Taken together these data demonstrate that Fbw7 is essential during cerebellar development, and identify N-terminally phosphorylated c-Jun as an important substrate of SCF(Fbw7) during neurogenesis.

From songs to synapses: molecular mechanisms of birdsong memory. Molecular mechanisms of auditory learning in songbirds involve immediate early genes, including zenk and arc, the ERK/MAPK pathway and synapsins

There are remarkable behavioral, neural, and genetic similarities between the way songbirds learn to sing and human infants learn to speak. Furthermore, the brain regions involved in birdsong learning, perception, and production have been identified and characterized in detail. In particular, the caudal medial nidopallium (the avian analog of the mammalian auditory-association cortex) has been found to contain the neural substrate of auditory memory, paving the way for analyses of the underlying molecular mechanisms. Recently, the zebra finch genome was sequenced, and annotated cDNA databases representing over 15,000 unique brain-expressed genes are available, enabling high-throughput gene expression analyses. Here we review the involvement of immediate early genes (e.g. zenk and arc), their downstream targets (e.g. synapsins), and their regulatory signaling pathways (e.g. MAPK/ERK) in songbird memory. We propose that in-depth investigations of zenk- and ERK-dependent cascades will help to further unravel the molecular basis of auditory memory.

Emerging role of mitogen-activated protein kinases in peripheral neuropathies

Among the different families of intracellular molecules that can be modulated during cell damage and repair, mitogen-activated protein kinases (MAPKs) are particularly interesting because they are involved in several intracellular pathways activated by injury and regeneration signals. Despite most of the studies have been performed in non-neurological models, recently a causal role for MAPKs has been postulated in central nervous system disorders. However, also in some peripheral neuropathies, MAPK changes can occur and these modifications might be relevant in the pathogenesis of the damage as well as during regeneration and repair. In this review, the current knowledge on the role of MAPKs in peripheral neuropathies will be discussed.

Identification of candidate transcriptional modulators involved in successful regeneration after nerve injury

Successful regeneration of injured neurons requires a complex molecular response that involves the expression, modification and transport of a large number of proteins. The identity of neuronal proteins responsible for the initiation of regenerative neurite outgrowth is largely unknown. Dorsal root ganglion (DRG) neurons display robust and successful regeneration following lesion of their peripheral neurite, whereas outgrowth of central neurites is weak and does not lead to functional recovery. We have utilized this differential response to gain insight in the early transcriptional events associated with successful regeneration. Surprisingly, our study shows that peripheral and central nerve crushes elicit very distinct transcriptional activation, revealing a large set of novel genes that are differentially regulated within the first 24 h after the lesion. Here we show that Ankrd1, a gene known to act as a transcriptional modulator, is involved in neurite outgrowth of a DRG neuron-derived cell line as well as in cultured adult DRG neurons. This gene, and others identified in this study, may be part of the transcriptional regulatory module that orchestrates the onset of successful regeneration.

Polychaete trunk neuroectoderm converges and extends by mediolateral cell intercalation

During frog and fish development, convergent extension movements transform the spherical gastrula into an elongated neurula. Such transformation of a ball- into a worm-shaped embryo is an ancestral and fundamental feature of bilaterian development, yet this is modified or absent in the protostome model organisms Caenorhabditis or Drosophila. In the polychaete annelid Platynereis dumerilii, early embryonic and larval stages resemble a sphere that subsequently elongates into worm shape. Cellular and molecular mechanisms of polychaete body elongation are yet unknown. Our in vivo time-lapse analysis of Platynereis axis elongation reveals that the polychaete neuroectoderm converges and extends by mediolateral cell intercalation. This occurs on both sides of the neural midline, the line of fusion of the slit-like blastopore. Convergent extension moves apart mouth and anus that are both derived from the blastopore. Tissue elongation is actin-dependent but microtubule-independent. Dependence on JNK activity and spatially restricted expression of strabismus indicates involvement of the noncanonical Wnt pathway. We detect a morphogenetic boundary between the converging and extending trunk neuroectoderm and the anterior otx-expressing head neuroectoderm that does not elongate. Our comparative analysis uncovers striking similarities but also differences between convergent extension in the polychaete and in the frog (the classical vertebrate model for convergent extension). Based on these findings, we propose that convergent extension movements of the trunk neuroectoderm represent an ancestral feature of bilaterian development that triggered the separation of mouth and anus along the elongating trunk.