Biomedical subjects

James H Schwartz

Publications and source records attributed to James H Schwartz.

9 recordsLinked to original sources

PubMed2006

Two mRNA-binding proteins regulate the distribution of syntaxin mRNA in Aplysia sensory neurons.

Targeting mRNAs to different functional domains within neurons is crucial to memory storage. In Aplysia sensory neurons, syntaxin mRNA accumulates at the axon hillock during long-term facilitation of sensory-motor neuron synapses produced by serotonin (5-HT). We find that the 3' untranslated region of Aplysia syntaxin mRNA has two targeting elements, the cytosolic polyadenylation element (CPE) and stem-loop double-stranded structures that appear to interact with mRNA-binding proteins CPEB and Staufen. Blocking the interaction between these targeting elements and their RNA-binding proteins abolished both accumulation at the axon hillock and long-term facilitation. CPEB, which we previously have shown to be upregulated after stimulation with 5-HT, is required for the relocalization of syntaxin mRNA to the axon hillock from the opposite pole in the cell body of the sensory neuron during long-term facilitation, whereas Staufen is required for maintaining the accumulation of the mRNA both at the axon hillock after the treatment with 5-HT and at the opposite pole in stable, unstimulated sensory neurons. Thus, the cooperative actions of the two mRNA-binding proteins serve to direct the distribution of an mRNA encoding a key synaptic protein.

Animals↗

PubMed2005

CREB-binding protein controls response to cocaine by acetylating histones at the fosB promoter in the mouse striatum.

Remodeling chromatin is essential for cAMP-regulated gene expression, necessary not only for development but also for memory storage and other enduring mental states. Histone acetylation and deacetylation mediate long-lasting forms of synaptic plasticity in Aplysia as well as cognition in mice. Here, we show that histone acetylation by the cAMP-response element binding protein (CREB)-binding protein (CBP) mediates sensitivity to cocaine by regulating expression of the fosB gene and its splice variant, DeltafosB, a transcription factor previously implicated in addiction. Using the chromatin immunoprecipitation assay with antibodies against histone H4 or CBP, we find that CBP is recruited to the fosB promoter to acetylate histone H4 in response to acute exposure to cocaine. We show that mutant mice that lack one allele of the CBP gene and have normal levels of fosB expression are less sensitive to chronic (10-day) administration of cocaine than are wild-type mice. This decreased sensitivity is correlated with decreased histone acetylation and results in decreased fosB expression and diminished accumulation of DeltafosB. Thus, CBP, which forms part of the promoter complex with CREB, mediates sensitivity to cocaine by acetylating histones.

Acetylation↗

PubMed2004

Long-term memory requires polyADP-ribosylation.

PolyADP-ribose-polymerase 1 is activated in neurons that mediate several forms of long-term memory in Aplysia. Because polyADP-ribosylation of nuclear proteins is a response to DNA damage in virtually all eukaryotic cells, it is surprising that activation of the polymerase occurs during learning and is required for long-term memory. We suggest that fast and transient decondensation of chromatin structure by polyADP-ribosylation enables the transcription needed to form long-term memory without strand breaks in DNA.

Animals↗

PubMed2004

The two regulatory subunits of aplysia cAMP-dependent protein kinase mediate distinct functions in producing synaptic plasticity.

Activation of the cAMP-dependent protein kinase (PKA) is critical for both short- and long-term facilitation in Aplysia sensory neurons. There are two types of the kinase, I and II, differing in their regulatory (R) subunits. We cloned Aplysia RII; RI was cloned previously. Type I PKA is mostly soluble in the cell body whereas type II is enriched at nerve endings where it is bound to two prominent A kinase-anchoring-proteins (AKAPs). Disruption of the binding of RII to AKAPs by Ht31, an inhibitory peptide derived from a human thyroid AKAP, prevents both the short- and the long-term facilitation produced by serotonin (5-HT). During long-term facilitation, RII is transcriptionally upregulated; in contrast, the amount of RI subunits decreases, and previous studies have indicated that the decrease is through ubiquitin-proteosome-mediated proteolysis. Experiments with antisense oligonucleotides injected into the sensory neuron cell body show that the increase in RII protein is essential for the production of long-term facilitation. Using synaptosomes, we found that 5-HT treatment causes RII protein to increase at nerve endings. In addition, using reverse transcription-PCR, we found that RII mRNA is transported from the cell body to nerve terminals. Our results suggest that type I operates in the nucleus to maintain cAMP response element-binding protein-dependent gene expression, and type II PKA acts at sensory neuron synapses phosphorylating proteins to enhance release of neurotransmitter. Thus, the two types of the kinase have distinct but complementary functions in the production of facilitation at synapses of an identified neuron.

Amino Acid Sequence↗

PubMed2003

Axonal transport of eukaryotic translation elongation factor 1alpha mRNA couples transcription in the nucleus to long-term facilitation at the synapse.

Long-term synaptic plasticity requires both gene expression in the nucleus and local protein synthesis at synapses. The effector proteins that link molecular events in the cell body with local maintenance of synaptic strength are not known. We now show that treatment with serotonin (5-HT) that produces long-term facilitation induces the Aplysia eukaryotic translation elongation factor 1alpha (Ap-eEF1A) as a late gene that might serve this coupling function in sensory neurons. Although the translation factor is induced, it is not transported into axon processes when the stimulation with 5-HT was restricted to the cell body. In contrast, its mRNA is transported when 5-HT was applied to both cell body and synapses. Intracellular injection of antisense oligonucleotides or antibodies that block the induction and expression of Ap-eEF1A do not affect the initial expression of long-term facilitation but do block its maintenance beyond 24 h. The transport of eEF1A protein and its mRNA to nerve terminals suggests that the translation factor plays a role in the local protein synthesis that is essential for maintaining newly formed synapses.

Animals↗

PubMed2003

p38 MAP kinase mediates both short-term and long-term synaptic depression in aplysia.

At Aplysia sensory-to-motor neuron synapses, the inhibitory neuropeptide Phe-Met-Arg-Phe-NH2 (FMRFa) produces depression, and serotonin (5-HT) produces facilitation. Short-term depression has been found to result from the activation of a phospholipase A2. The released arachidonate is metabolized by 12-lipoxygenase to active second messengers. We find that FMRFa leads to the phosphorylation and activation of p38 mitogen-activated protein (MAP) kinase. Short-term depression and the release of arachidonate are blocked by the specific p38 kinase inhibitor SB 203580. Both the inhibitor and an affinity-purified antibody raised against recombinant Aplysia p38 kinase injected into sensory neurons prevented long-term depression, which depends on the phosphorylation of translation factors cAMP response element-binding protein 2 (CREB2) and activating transcription factor 2. Facilitation produced by 5-HT, on the other hand, inactivates p38 kinase. Chromatin immunoprecipitation assays indicate that p38 kinase activates CREB2. p38 kinase also is pivotal in the bidirectional regulation of synaptic plasticity: when the kinase is inhibited, brief treatment with 5-HT that normally produces only short-term facilitation now results in long-term facilitation. Conversely, in sensory neurons injected with the activated kinase, long-term facilitation is blocked, and brief exposure to FMRFa, which normally results in short-term depression, results in long-term depression. We conclude that p38 kinase, which itself is bidirectionally regulated by FMRFa and 5-HT, acts as a modulator of synaptic plasticity by positively regulating depression and serving as an inhibitory constraint for facilitation.

Activating Transcription Factor 2↗

PubMed2003

Ubiquitination, protein turnover, and long-term synaptic plasticity.

For at least half a century, alteration of synaptic strength through growth at specific nerve terminals has been favored as the mechanism underlying long-term changes in behavior and synaptic plasticity. Although new proteins for synapses can either be synthesized locally or transported from the cell body, recent work on the postsynaptic element (dendritic spines) of cortical excitatory synapses indicates that transmission can also be modified by controlling the density of alpha-amino-3-hydroxy-5-methylisoxazole-4-proprionic acid receptors (AMPARs) in the postsynaptic density (PSD). This regulation is mediated by mono-ubiquitination, which governs turnover of AMPAR subunits by determining whether the endocytosed subunits are sent to lysosomes to be degraded or recycled back to the membrane by exocytosis. Also important is activity-dependent multi-ubiquitination and degradation of proteins that make up the scaffolding complexes that confine receptors to the PSD.

Animals↗

PubMed2003

The cytoplasmic polyadenylation element binding protein and polyadenylation of messenger RNA in Aplysia neurons.

Translation of some mRNAs in nerve terminals has been shown to be regulated by polyadenylation in an experience-dependent manner. The transcripts whose translation is controlled by regulated polyadenylation contain the cytoplasmic polyadenylation element (CPE), which binds to the highly conserved CPE-binding protein (CPEB). In Aplysia, neuron-specific actin mRNA, which has a CPE in its 3' UTR, is located both in cell bodies and at nerve endings (synaptosomes). We found that actin mRNA from pleural ganglion sensory neurons becomes polyadenylated during long-term facilitation produced by treatment with serotonin or 8-bromo cAMP. We cloned two isoforms of CPEB (ApCPEB77 and ApCEPB49) from Aplysia nervous tissue. The larger form, which is predominant in nervous tissue, is similar to p82, the clam binding protein, as well as to vertebrate CPEBs. Moreover, synaptosomal actin mRNAs are polyadenylated following the treatment with 5-HT. Since both CPEB and polyadenylated actin mRNA are present in synaptosomes and synaptosomal actin protein increases during long-term facilitation, we suggest that the translation of actin message in nerve endings is up-regulated by polyadenylation to grow new synapses.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed2002

Integration of long-term-memory-related synaptic plasticity involves bidirectional regulation of gene expression and chromatin structure.

Excitatory and inhibitory inputs converge on single neurons and are integrated into a coherent output. Although much is known about short-term integration, little is known about how neurons sum opposing signals for long-term synaptic plasticity and memory storage. In Aplysia, we find that when a sensory neuron simultaneously receives inputs from the facilitatory transmitter 5-HT at one set of synapses and the inhibitory transmitter FMRFamide at another, long-term facilitation is blocked and synapse-specific long-term depression dominates. Chromatin immunoprecipitation assays show that 5-HT induces the downstream gene C/EBP by activating CREB1, which recruits CBP for histone acetylation, whereas FMRFa leads to CREB1 displacement by CREB2 and recruitment of HDAC5 to deacetylate histones. When the two transmitters are applied together, facilitation is blocked because CREB2 and HDAC5 displace CREB1-CBP, thereby deacetylating histones.

Acetylation↗