Papers by Kelsey C. Martin
Neuron, Dec 1, 2004
transported into the nucleus (Davis, 1995). Cytoplasmic 2 Brain Research Institute proteins beari... more transported into the nucleus (Davis, 1995). Cytoplasmic 2 Brain Research Institute proteins bearing nuclear localization signals (NLS) are 3 Department of Psychiatry targeted to the nucleus and transported through the and Biobehavioral Sciences pores by a large family of soluble nuclear transport fac-4 Department of Physiology tors known as importins or karyopherins (Weis, 2002). 5 Department of Biological Chemistry In the classical nuclear import pathway, importin ␣ rec-6 Neuropsychiatric Institute ognizes and binds to the NLS on the cargo protein and University of California, Los Angeles also binds to importin 1, which then docks the complex Los Angeles, California 90095 at the nuclear pore and mediates translocation from the cytoplasm into the nucleus. Six distinct importin ␣ isoforms have been identified in human, five have been Summary identified in mouse, and three have been identified in Drosophila, and in this report we describe an importin The requirement for transcription during long-lasting ␣ isoform that we identified in Aplysia. plasticity indicates that signals generated at the syn-While the classical active nuclear import pathway has apse must be transported to the nucleus. We have been well characterized in nonneuronal cells, little is investigated whether the classical active nuclear imknown about its function in neurons. Earlier studies port pathway mediates intracellular retrograde signal demonstrated that rhodaminated human serum albumin transport in Aplysia sensory neurons and rodent hipmicroinjected into growth cones of cultured Aplysia neupocampal neurons. We found that importins localize rons was transported to the cell nucleus when the albuto distal neuronal processes, including synaptic commin was coupled to an NLS but remained in the growth partments, where they are well positioned to mediate cone in the absence of an NLS, indicating that the active synapse to nucleus signaling. In Aplysia, stimuli known nuclear import machinery was present in the growth to produce long-lasting but not short-lasting facilitacone of Aplysia neurons and that it could function to tion triggered importin nuclear translocation. In hippotransport molecules to the nucleus (Ambron et al., 1992). campal neurons, NMDA receptor activation but not Several groups have reported expression of importin ␣ depolarization induced importin nuclear translocation. in the brain (Kohler et al., 1997, 1999; Prieve et al., 1996), We further showed that LTP-inducing stimuli recruited and immunohistochemical analyses have suggested active nuclear import in hippocampal slices. Together that neuronal importin ␣ and  are present not only in with our finding that long-term facilitation of Aplysia somatic regions, but also in hippocampal and cerebellar sensory-motor synapses required active nuclear imdendrites (Kamei et al., 1999). More recently, Fainzilber port, our results indicate that regulation of the active and colleagues (Hanz et al., 2003) have reported that nuclear import pathway plays a critical role in transimportin ␣ and  are present in motor neuron axons, porting synaptically generated signals into the nucleus that importin  mRNA is translated in the axon following during learning-related forms of plasticity. crush injury, and that the active nuclear import pathway functions in signaling from injured axons to initiate tran-Introduction scription-dependent regeneration. In this study, we examine the role of the classical Long-lasting forms of learning-related synaptic plasticactive nuclear import pathway in transporting signals ity require new transcription (Alberini, 1999), indicating from the cytoplasm into the nucleus using two experithat signals generated at the synapse must be transmental models that undergo learning-related synaptic ported to the nucleus, where they are converted into strength changes: Aplysia sensory-motor neurons and changes in gene expression. Little is known about the rodent hippocampal neurons. The sensory and motor cellular mechanisms that target and transport synaptineurons that underlie sensitization and classical condically activated second messengers and transcription tioning of the gill withdrawal reflex in Aplysia form monofactors to the nucleus. The extreme polarity of neurons synaptic connections in culture, and these synapses presents a special set of challenges for intracellular sigundergo both short-and long-lasting strengthening or nal transduction, because the distance between the synfacilitation in response to electrical and pharmacological apse and nucleus can be extremely large. Thus, a signal stimuli (Pittenger and Kandel, 2003). Long-term facilitafrom a distal synapse must first travel the length of the tion (LTF) of cultured Aplysia sensory-motor synapses axon or dendrite and then through the somatic cytois elicited by application of five spaced pulses of the plasm to reach the nuclear envelope. modulatory neurotransmitter serotonin (5-HT), which leads to a transcription-dependent, persistent increase in synaptic strength (Montarolo et al., 1986). Localized
Frontiers in Molecular Neuroscience, Jan 21, 2024
Aging-related memory impairment and pathological memory disorders such as Alzheimer's disease dif... more Aging-related memory impairment and pathological memory disorders such as Alzheimer's disease differ between males and females, and yet little is known about how aging-related changes in the transcriptome and chromatin environment differ between sexes in the hippocampus. To investigate this question, we compared the chromatin accessibility landscape and gene expression/ alternative splicing pattern of young adult and aged mouse hippocampus in both males and females using ATAC-seq and RNA-seq. We detected significant aging-dependent changes in the expression of genes involved in immune response and synaptic function and aging-dependent changes in the alternative splicing of myelin sheath genes. We found significant sex-bias in the expression and alternative splicing of hundreds of genes, including aging-dependent female-biased expression of myelin sheath genes and aging-dependent malebiased expression of genes involved in synaptic function. Aging was associated with increased chromatin accessibility in both male and female hippocampus, especially in repetitive elements, and with an increase in LINE-1 transcription. We detected significant sex-bias in chromatin accessibility in both autosomes and the X chromosome, with male-biased accessibility enriched at promoters and CpG-rich regions. Sex differences in gene expression and chromatin accessibility were amplified with aging, findings that may shed light on sex differences in aging-related and pathological memory loss.
The Journal of Neuroscience, Sep 1, 2000
The lateral amygdala (LA) is thought to be critical for the specific acquisition of conditioned f... more The lateral amygdala (LA) is thought to be critical for the specific acquisition of conditioned fear, and the emotionally charged memories related to fear are thought to require a form of synaptic plasticity related to long-term potentiation (LTP). Is LTP in the lateral amygdala enduring, and, if so, does it require gene expression and the synthesis of new protein? Using brain slices, we have examined the molecular-signaling pathway of LTP in the cortico-amygdala and the thalamo-amygdala pathways. We find that a single high-frequency train of stimuli induces a transient LTP (E-LTP); by contrast, five repeated high-frequency trains induce an enduring late phase of LTP (L-LTP), which is dependent on gene expression and on new protein synthesis. In both pathways the late phase of LTP is mediated by protein kinase A (PKA) and mitogen-activated protein kinase (MAPK). Application of the adenylyl cyclase activator forskolin induced L-LTP in both pathways, and this potentiation is blocked by inhibitors of protein synthesis. The late phase of LTP also is modulated importantly by -adrenergic agonists. An inhibitor of -adrenergic receptors blocks L-LTP; conversely, application of a -adrenergic agonist induces the L-LTP. Immunocytochemical studies show that both repeated tetanization and application of forskolin stimulate the phosphorylation of cAMP response element-binding proteins (CREB) in cells of the lateral nucleus of the amygdala. These results suggest that PKA and MAPK are critical for the expression of a persistent phase of LTP in the lateral amygdala and that this late component requires the synthesis of new protein and mRNA.
The Journal of Neuroscience, Oct 15, 2003
Local protein synthesis is required for long-lasting synapse-specific plasticity in cultured Aply... more Local protein synthesis is required for long-lasting synapse-specific plasticity in cultured Aplysia sensorimotor synapses. To identify synaptically localized mRNAs, we prepared a cDNA library from isolated sensory neurites. By sequence analysis, we estimate that the library contains 263 distinct mRNAs, with 98 of these mRNAs constituting 70% of all clones. The localized transcripts are enriched for mRNAs encoding cytoskeletal elements and components of the translational machinery. In situ hybridization confirms that the mRNAs for at least eight of these transcripts are present in distal neurites. Immunocytochemistry reveals that serotonin regulates the translation of one of the localized mRNAs, that encoding ␣1-tubulin. Our identification of mRNAs encoding cytoskeletal elements suggests that local protein synthesis is required for the growth of new synaptic connections associated with persistent synaptic strengthening. Our finding of mRNAs encoding components of the translational machinery suggests that local protein synthesis serves to increase the translational capacity of synapses.
Proceedings of the National Academy of Sciences of the United States of America, Nov 21, 1995
While previous studies have demonstrated that synaptotagmin plays an essential role in evoked neu... more While previous studies have demonstrated that synaptotagmin plays an essential role in evoked neurotransmitter release, it has been difficult to determine whether it acts to facilitate or inhibit release. To address this question, we used acute genetic manipulations to alter the expression-of synaptotagmin in Aplysia neurons. Transient overexpression of synaptotagmin in acutely dissected cholinergic neurons and in cultured glutaminergic neurons decreased the amplitude of the excitatory postsynaptic potential (EPSP) by 32% and 26%, respectively. In contrast, treatment of cultured presynaptic neurons with synaptotagmin antisense oligonucleotides increased the amplitude of the EPSP by 50-75%. These results are consistent with a role of synaptotagmin as an inhibitor of release.
The Journal of Neuroscience, Dec 16, 2009
Synaptic plasticity, the capacity of neurons to change the strength of their connections with exp... more Synaptic plasticity, the capacity of neurons to change the strength of their connections with experience, provides a mechanism for learning and memory in the brain. Long-term plasticity requires new transcription, indicating that synaptically generated signals must be transported to the nucleus. Previous studies have described a role for importin nuclear transport adaptors in mediating the retrograde transport of signals from synapse to nucleus during plasticity. Here, we investigated the possibility that stimulus-induced translocation of importins from synapse to nucleus involves activity-dependent anchoring of importins at the synapse. We show that importin ␣ binds to a nuclear localization signal (NLS) present in the cytoplasmic tail of NR1-1a. This interaction is disrupted by activation of NMDA receptors in cultured neurons and by stimuli that trigger late-phase, but not early-phase, long-term potentiation of CA3-CA1 synapses in acute hippocampal slices. In vitro PKC phosphorylation of GST-NR1-1a abolishes its ability to bind importin ␣ in brain lysates, and the interaction of importin ␣ and NR1 in neurons is modulated by PKC activity. Together, our results indicate that importin ␣ is tethered at the postsynaptic density by binding to the NLS present in NR1-1a. This interaction is activity dependent, with importin ␣ being released following NMDA receptor activation and phosphorylation rendering it available to bind soluble cargoes and transport them to the nucleus during transcription-dependent forms of neuronal plasticity.
The Mali Rural Health Project (Project Sante Rurale PSR) was designed as a model to extend rudime... more The Mali Rural Health Project (Project Sante Rurale PSR) was designed as a model to extend rudimentary cost-efficient replicable health care services by training community volunteers to give treatment and to maintain a program financed locally. At the request of the Mali Ministry to Public Health USAID through a subcontractor Harvard Institute for International Development (HIID) set up a demonstration project in 2 sites Koro district in east central Mali and Yelimane district in the West. Costs to maintain and replicate the project amounted to additional public expenditure equal to Malis total per capita health expenditure ($2) per resident of the target areas. Supplies mostly the drugs penicillin tablets chloroquine sulfa eye ointment and aspirin were to make up $.40 of this. An elaborate analysis of costs of the program is presented. 2 health workers were to be trained in each of 40 villages per site for 3-10 days. They were expected to be able to dispense medications reimbursed by villagers and to promote health behaviors for payment in case or kind. Trained traditional birth attendants were expected to diagnose and refer complicated pregnancies and deliveries although no facilities were available closer than the regional hospital for surgery. After a flurry of medicine dispensing activity declined. Although data were to be collected to evaluate the impact of the project on health by provincial health officials only the workers recall of knowledge and the populations willingness to share in costs were available for assessment. The transportation aspect of the program via mopeds was its most difficult problem. Sections on obstacles to health care program design recruitment training supervision and supply reiterate the failures of the PSR model. Implications for similar projects elsewhere are discussed.
F1000 - Post-publication peer review of the biomedical literature, 2003
F1000 - Post-publication peer review of the biomedical literature, 2003
F1000 - Post-publication peer review of the biomedical literature, 2003
Journal of Cell Biology, 2021
The formation and plasticity of neuronal circuits relies on dynamic activity-dependent gene expre... more The formation and plasticity of neuronal circuits relies on dynamic activity-dependent gene expression. Although recent work has revealed the identity of important transcriptional regulators and of genes that are transcribed and translated in response to activity, relatively little is known about the cell biological mechanisms by which activity alters the nuclear proteome of neurons to link neuronal stimulation to transcription. Using nucleus-specific proteomic mapping in silenced and stimulated neurons, we uncovered an understudied mechanism of nuclear proteome regulation: activity-dependent proteasome-mediated degradation. We found that the tumor suppressor protein PDCD4 undergoes rapid stimulus-induced degradation in the nucleus of neurons. We demonstrate that degradation of PDCD4 is required for normal activity-dependent transcription and that PDCD4 target genes include those encoding proteins critical for synapse formation, remodeling, and transmission. Our findings highlight t...
The Journals of Gerontology: Series A
Activity-dependent gene expression is critical for synapse development and plasticity. To elucida... more Activity-dependent gene expression is critical for synapse development and plasticity. To elucidate novel mechanisms linking neuronal activity to changes in transcription, we compared the nuclear proteomes of tetrodotoxin-silenced and bicuculline-stimulated cultured rodent neurons using nuclear-localized APEX2 proximity biotinylation and mass spectrometry. The tumor suppressor protein PDCD4 was enriched in the silenced nuclear proteome, and PDCD4 levels rapidly decreased in the nucleus and cytoplasm of stimulated neurons. The activity-dependent decrease of PDCD4 was prevented by inhibitors of both PKC and proteasome activity and by a phospho-incompetent mutation of Ser71 in the βTRCP ubiquitin ligase-binding motif of PDCD4. We compared the activity-dependent transcriptomes of neurons expressing wildtype or degradation-resistant (S71A) PDCD4. We identified 91 genes as PDCD4 targets at the transcriptional level, including genes encoding proteins critical for synapse formation, remodel...
Science (New York, N.Y.), Jan 18, 2015
Cell, 1991
Because influenza virus replicates in the nucleus and buds from the plasma membrane, its ribonucl... more Because influenza virus replicates in the nucleus and buds from the plasma membrane, its ribonucleoproteins (RNPs) must undergo bidirectional transport across the nuclear membrane. Export from the nucleus to the cytoplasm was found to depend on the viral matrix protein (M1). M1 associated with ...
Nature Structural & Molecular Biology
A localized transcriptome at the synapse facilitates synapse-, stimulus-, and transcript-specific... more A localized transcriptome at the synapse facilitates synapse-, stimulus-, and transcript-specific synthesis of the local proteome in response to neuronal activity. While enzyme-mediated mRNA modifications have been shown to regulate cellular mRNA turnover and translation, the role of these modifications in regulating synaptic RNA has not been studied. We established low-input m6A-seq of synaptosomal RNA to determine the chemically modified local transcriptome in healthy adult mouse forebrain and identified 4,329 selectively enriched m6A RNA peaks in 2,987 genes, which we refer to as the synaptic m6A epitranscriptome (SME). SME is functionally enriched in synthesis and modulation of tripartite synapses, and in pathways implicated in neurodevelopmental and neuropsychiatric diseases. Interrupting m6A-mediated regulation via knockdown of reader YTHDF1 in hippocampal neurons alters expression of SME member Apc, and causes synaptic malfunctions manifesting immature spine morphology and da...
Nature neuroscience, Jan 10, 2018
In the version of this article initially published, a Supplementary Fig. 6f was cited in the last... more In the version of this article initially published, a Supplementary Fig. 6f was cited in the last paragraph of the Results. No such panel exists; the citation has been deleted. The error has been corrected in the HTML and PDF versions of the article.
Nature neuroscience, 2018
A localized transcriptome at the synapse facilitates synapse-, stimulus- and transcript-specific ... more A localized transcriptome at the synapse facilitates synapse-, stimulus- and transcript-specific local protein synthesis in response to neuronal activity. While enzyme-mediated mRNA modifications are known to regulate cellular mRNA turnover, the role of these modifications in regulating synaptic RNA has not been studied. We established low-input mA-sequencing of synaptosomal RNA to determine the chemically modified local transcriptome in healthy adult mouse forebrains and identified 4,469 selectively enriched mA sites in 2,921 genes as the synaptic mA epitranscriptome (SME). The SME is functionally enriched in synthesis and modulation of tripartite synapses and in pathways implicated in neurodevelopmental and neuropsychiatric diseases. Interrupting mA-mediated regulation via knockdown of readers in hippocampal neurons altered expression of SME member Apc, resulting in synaptic dysfunction including immature spine morphology and dampened excitatory synaptic transmission concomitant w...
Neuron, Jan 4, 2018
Astrocytes are complex bushy cells that serve important functions through close contacts between ... more Astrocytes are complex bushy cells that serve important functions through close contacts between their processes and synapses. However, the spatial interactions and dynamics of astrocyte processes relative to synapses have proven problematic to study in adult living brain tissue. Here, we report a genetically targeted neuron-astrocyte proximity assay (NAPA) to measure astrocyte-synapse spatial interactions within intact brain preparations and at synaptic distance scales. The method exploits resonance energy transfer between extracellularly displayed fluorescent proteins targeted to synapses and astrocyte processes. We validated the method in the striatal microcircuitry following in vivo expression. We determined the proximity of striatal astrocyte processes to distinct neuronal input pathways, to D1 and D2 medium spiny neuron synapses, and we evaluated how astrocyte-to-excitatory synapse proximity changed following cortical afferent stimulation, during ischemia and in a model of Hun...
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Papers by Kelsey C. Martin