Alarcon, Juan Marcos

Alarcon, Juan Marcos

Biography

Our laboratory explores how experiences change brain function in neurotypical laboratory rodents as well as in animal models of brain disease. My background training in electrophysiology started with ion channels biophysics during my PhD under Dr. Eduardo Rojas (Univ. of Chile), and then with hippocampal synaptic plasticity function during my post-doc under Dr. Eric Kandel (Columbia Univ.). At SUNY Downstate Health Sciences University (DHSU), I joined an expert and collegial team of scientists that allowed me to expand our investigational scope to explore neurobiological processes at the gene expression level (e.g. RNAseq), synaptic function level (e.g. synaptic and neuronal electrophysiology), neuronal ensemble organization (e.g. activity-dependent immediate early gene tagging), and behavior (e.g. rodent memory tasks). Our current research projects aim to test the connection between neurodevelopmental mechanisms and brain function in animal models of autism. Inspired by this and concomitant with DHSU mission, I co-developed and co-lead with Dr. Jenny Libien an R25 summer research course for young under-represented minorities to investigate the neurobiology of autism spectrum disorders. Overall, our goal is to provide a deeper insight on the nature and mechanisms of neurodevelopmental disorders.

Publication Search Results

Now showing 1 - 10 of 30

Open Access
Behavioral alterations are associated with vitamin B12 deficiency in the transcobalamin receptor/CD320 KO mouse
(Public Library of Science (PLoS), 2017-05-18) Arora, Kaveri; Sequeira, Jeffrey M.; Hernández, Alejandro I.; Alarcon, Juan M.; Quadros, Edward V.
Vitamin B12 (cobalamin) deficiency is prevalent worldwide and causes megaloblastic anemia and neurologic deficits. While the anemia can be treated, the neurologic deficits can become refractive to treatment as the disease progresses. Therefore, timely intervention is critical for a favorable outcome. Moreover, the metabolic basis for the neuro-pathologic changes and the role of cobalamin deficiency in the pathology still remains unexplained. Using a transcobalamin receptor / CD320 knockout mouse that lacks the receptor for cellular uptake of transcobalamin bound cobalamin, we aimed to determine whether cobalamin deficiency in the central nervous system produced functional neurologic deficits in the mouse that would parallel those observed in humans. Our behavioral analyses indicate elevated anxiety and deficits in learning, memory and set-shifting of a spatial memory task in the KO mouse. Consistent with the behavioral deficits, the knockout mouse shows impaired expression of the early phase of hippocampal long-term potentiation along with reduced expression of GluR1, decreased brain mass and a significant reduction in the size of nuclei of the hippocampal pyramidal neurons. Our study suggests that the CD320 knockout mouse develops behavioral deficits associated with cobalamin deficiency and therefore could provide a model to understand the metabolic and genetic basis of neuro-pathologic changes due to cobalamin deficiency.
Open Access
Gene Expression Profiling of Facilitated L-LTP in VP16-CREB Mice Reveals that BDNF Is Critical for the Maintenance of LTP and Its Synaptic Capture
(Elsevier BV, 2005-10) Barco, Angel; Patterson, Susan; Alarcon, Juan M.; Gromova, Petra; Mata-Roig, Manuel; Morozov, Alexei; Kandel, Eric R.
Expression of VP16-CREB, a constitutively active form of CREB, in hippocampal neurons of the CA1 region lowers the threshold for eliciting the late, persistent phase of long-term potentiation (L-LTP) in the Schaffer collateral pathway. This VP16-CREB-mediated L-LTP differs from the conventional late phase of LTP in not being dependent on new transcription. This finding suggests that in the transgenic mice the mRNA transcript(s) encoding the protein(s) necessary for this form of L-LTP might already be present in CA1 neurons in the basal condition. We used high-density oligonucleotide arrays to identify the mRNAs differentially expressed in the hippocampus of transgenic and wild-type mice. We then explored the contribution of the most prominent candidate genes revealed by our screening, namely prodynorphin, BDNF, and MHC class I molecules, to the facilitated LTP of VP16-CREB mice. We found that the overexpression of brain-derived neurotrophic factor accounts for an important component of this phenotype.
Open Access
cAMP Response Element-Binding Protein-Mediated Gene Expression Increases the Intrinsic Excitability of CA1 Pyramidal Neurons
(Society for Neuroscience, 2007-12-12) Lopez de Armentia, Mikel; Jancic, Dragana; Olivares, Roman; Alarcon, Juan M.; Kandel, Eric R.; Barco, Angel
To investigate the role of CREB-mediated gene expression on the excitability of CA1 pyramidal neurons, we obtained intracellular recordings from pyramidal neurons of transgenic mice expressing a constitutively active form of CREB, VP16-CREB, in a regulated and restricted manner. We found that transgene expression increased the neuronal excitability and inhibited the slow and medium afterhyperpolarization currents. These changes may contribute to the reduced threshold for LTP observed in these mice. When strong transgene expression was turned on for prolonged period of time, these mice also showed a significant loss of hippocampal neurons and sporadic epileptic seizures. These deleterious effects were dose dependent and could be halted, but not reversed by turning off transgene expression. Our experiments reveal a new role for hippocampal CREB-mediated gene expression, identify the slow afterhyperpolarization as a primary target of CREB action, provide a new mouse model to investigate temporal lobe epilepsy and associated neurodegeneration, and illustrate the risks of cell death associated to a sustained manipulation of this pathway. As a result, our study has important implications for both the understanding of the cellular bases of learning and memory and the consideration of therapies targeted to the CREB pathway.
Open Access
Hippocampal transcriptomic responses to enzyme‐mediated cellular dissociation
(Wiley, 2019-05-14) Harris, Rayna M.; Kao, Hsin‐Yi; Alarcon, Juan Marcos; Hofmann, Hans A.; Fenton, André A.
Single-neuron gene expression studies may be especially important for understanding nervous system structure and function because of the neuron-specific functionality and plasticity that defines functional neural circuits. Cellular dissociation is a prerequisite technical manipulation for single-cell and single cell-population studies, but the extent to which the cellular dissociation process affects neural gene expression has not been determined. This information is necessary for interpreting the results of experimental manipulations that affect neural function such as learning and memory. The goal of this research was to determine the impact of cellular dissociation on brain transcriptomes. We compared gene expression of microdissected samples from the dentate gyrus (DG), CA3, and CA1 subfields of the mouse hippocampus either prepared by a standard tissue homogenization protocol or subjected to enzymatic digestion used to dissociate cells within tissues. We report that compared to homogenization, enzymatic dissociation alters about 350 genes or 2% of the hippocampal transcriptome. While only a few genes canonically implicated in long-term potentiation and fear memory change expression levels in response to the dissociation procedure, these data indicate that sample preparation can affect gene expression profiles, which might confound interpretation of results depending on the research question. This study is important for the investigation of any complex tissues as research effort moves from subfield level analysis to single cell analysis of gene expression.
Open Access
Nucleolar Integrity Is Required for the Maintenance of Long-Term Synaptic Plasticity
(Public Library of Science (PLoS), 2014-08-04) Allen, Kim D.; Gourov, Andrei V.; Harte, Christopher; Gao, Peng; Lee, Clarice; Sylvain, Darlene; Splett, Joshua M.; Oxberry, William C.; van de Nes, Paula S.; Troy-Regier, Matthew J.; Wolk, Jason; Alarcon, Juan M.; Hernández, A. Iván
Long-term memory (LTM) formation requires new protein synthesis and new gene expression. Based on our work in Aplysia, we hypothesized that the rRNA genes, stimulation-dependent targets of the enzyme Poly(ADP-ribose) polymerase-1 (PARP-1), are primary effectors of the activity-dependent changes in synaptic function that maintain synaptic plasticity and memory. Using electrophysiology, immunohistochemistry, pharmacology and molecular biology techniques, we show here, for the first time, that the maintenance of forskolin-induced late-phase long-term potentiation (L-LTP) in mouse hippocampal slices requires nucleolar integrity and the expression of new rRNAs. The activity-dependent upregulation of rRNA, as well as L-LTP expression, are poly(ADP-ribosyl)ation (PAR) dependent and accompanied by an increase in nuclear PARP-1 and Poly(ADP) ribose molecules (pADPr) after forskolin stimulation. The upregulation of PARP-1 and pADPr is regulated by Protein kinase A (PKA) and extracellular signal-regulated kinase (ERK)--two kinases strongly associated with long-term plasticity and learning and memory. Selective inhibition of RNA Polymerase I (Pol I), responsible for the synthesis of precursor rRNA, results in the segmentation of nucleoli, the exclusion of PARP-1 from functional nucleolar compartments and disrupted L-LTP maintenance. Taken as a whole, these results suggest that new rRNAs (28S, 18S, and 5.8S ribosomal components)--hence, new ribosomes and nucleoli integrity--are required for the maintenance of long-term synaptic plasticity. This provides a mechanistic link between stimulation-dependent gene expression and the new protein synthesis known to be required for memory consolidation.
Open Access
A Molecular Circuit Composed of CPEB-1 and c-Jun Controls Growth Hormone-Mediated Synaptic Plasticity in the Mouse Hippocampus
(Society for Neuroscience, 2008-08-20) Zearfoss, N. Ruth; Alarcon, Juan Marcos; Trifilieff, Pierre; Kandel, Eric; Richter, Joel D.
Cytoplasmic polyadenylation element binding protein 1 (CPEB-1) resides at postsynaptic sites in hippocampal neurons in which it controls polyadenylation-induced translation. CPEB-1 knock-out (KO) mice display defects in some forms of synaptic plasticity and hippocampal-dependent memories. To identify CPEB-1-regulated mRNAs, we used proteomics to compare polypeptides in wild-type (WT) and CPEB-1 KO hippocampus. Growth hormone (GH) was reduced in the KO hippocampus, as were the GH signaling molecules phospho-JAK2 and phospho-STAT3. GH mRNA and pre-mRNA were reduced in the KO hippocampus, suggesting that CPEB-1 controls GH transcription. The transcription factor c-Jun, which binds the GH promoter, was also reduced in the KO hippocampus, as was its ability to coimmunoprecipitate chromatin containing the GH promoter. CPEB-1 binds c-Jun 3' untranslated region CPEs in vitro and coimmunoprecipitates c-Jun RNA in vivo. GH induces long-term potentiation (LTP) when applied to hippocampal slices from WT and CPEB-1 KO mice, but the magnitude of LTP induced by GH in KO mice is reduced. Pretreatment with GH did not reverse the LTP deficit observed in KO mice after theta-burst stimulation (TBS). Cordycepin, an inhibitor of polyadenylation, disrupted LTP induced by either GH application or TBS. Finally, GH application to hippocampal slices induced JAK2 phosphorylation in WT but not KO animals. These results indicate that CPEB-1 control of c-Jun mRNA translation regulates GH gene expression and resulting downstream signaling events (e.g., synaptic plasticity) in the mouse hippocampus.
Open Access
New ribosomes for new memories?
(Informa UK Limited, 2015-04-15) Hernández, A Iván; Alarcon, Juan M; Allen, Kim D
Widely thought to be a housekeeping process, the regulation and synthesis of rRNA emerges as a potentially central mechanism for the maintenance of synaptic plasticity and memory. We have recently shown that an essential component of late-phase synaptic plasticity is rRNA biosynthesis - the rate-limiting step in the production of new ribosomes. We hypothesize that a particular population of ribosomes is generated upon learning-associated neural activity to alter the rate of synthesis of plasticity factors at tagged synapses that will support the maintenance of synaptic plasticity and memory.
Open Access
Normal CA1 Place Fields but Discoordinated Network Discharge in a Fmr1-Null Mouse Model of Fragile X Syndrome
(Elsevier BV, 2018-02) Talbot, Zoe Nicole; Sparks, Fraser Todd; Dvorak, Dino; Curran, Bridget Mary; Alarcon, Juan Marcos; Fenton, André Antonio
Silence of FMR1 causes loss of fragile X mental retardation protein (FMRP) and dysregulated translation at synapses, resulting in the intellectual disability and autistic symptoms of fragile X syndrome (FXS). Synaptic dysfunction hypotheses for how intellectual disabilities like cognitive inflexibility arise in FXS predict impaired neural coding in the absence of FMRP. We tested the prediction by comparing hippocampus place cells in wild-type and FXS-model mice. Experience-driven CA1 synaptic function and synaptic plasticity changes are excessive in Fmr1-null mice, but CA1 place fields are normal. However, Fmr1-null discharge relationships to local field potential oscillations are abnormally weak, stereotyped, and homogeneous; also, discharge coordination within Fmr1-null place cell networks is weaker and less reliable than wild-type. Rather than disruption of single-cell neural codes, these findings point to invariant tuning of single-cell responses and inadequate discharge coordination within neural ensembles as a pathophysiological basis of cognitive inflexibility in FXS. VIDEO ABSTRACT.
Open Access
Noncanonical cytoplasmic poly(A) polymerases regulate RNA levels, alternative RNA processing, and synaptic plasticity but not hippocampal-dependent behaviours
(Informa UK Limited, 2020-10-12) Mansur, Fernanda; Alarcon, Juan Marcos; Stackpole, Emily E.; Wang, Ruijia; Richter, Joel D.
Noncanonical poly(A) polymerases are frequently tethered to mRNA 3' untranslated regions and regulate poly(A) tail length and resulting translation. In the brain, one such poly(A) polymerase is Gld2, which is anchored to mRNA by the RNA-binding protein CPEB1 to control local translation at postsynaptic regions. Depletion of CPEB1 or Gld2 from the mouse hippocampus results in a deficit in long-term potentiation (LTP), but only depletion of CPEB1 alters animal behaviour. To test whether a related enzyme, Gld4, compensates for the lack of Gld2, we separately or simultaneously depleted both proteins from hippocampal area CA1 and again found little change in animal behaviour, but observed a deficit in LTP as well as an increase in long-term depression (LTD), two forms of protein synthesis-dependent synaptic plasticity. RNA-seq data from Gld2, Gld4, and Gld2/Gld4-depleted hippocampus show widespread changes in steady state RNA levels, alternative splicing, and alternative poly(A) site selection. Many of the RNAs subject to these alterations encode proteins that mediate synaptic function, suggesting a molecular foundation for impaired synaptic plasticity.
Open Access
Persistent increases of PKMζ in memory‐activated neurons trace LTP maintenance during spatial long‐term memory storage
(Wiley, 2021-03-28) Hsieh, Changchi; Tsokas, Panayiotis; Grau‐Perales, Alejandro; Lesburguères, Edith; Bukai, Joseph; Khanna, Kunal; Chorny, Joelle; Chung, Ain; Jou, Claudia; Burghardt, Nesha S.; Denny, Christine A.; Flores‐Obando, Rafael E.; Hartley, Benjamin Rush; Rodríguez Valencia, Laura Melissa; Hernández, A. Iván; Bergold, Peter J.; Cottrell, James E.; Alarcon, Juan Marcos; Fenton, André Antonio; Sacktor, Todd Charlton
PKMζ is an autonomously active PKC isoform crucial for the maintenance of synaptic long-term potentiation (LTP) and long-term memory. Unlike other kinases that are transiently stimulated by second messengers, PKMζ is persistently activated through sustained increases in protein expression of the kinase. Therefore, visualizing increases in PKMζ expression during long-term memory storage might reveal the sites of its persistent action and thus the location of memory-associated LTP maintenance in the brain. Using quantitative immunohistochemistry validated by the lack of staining in PKMζ-null mice, we examined the amount and distribution of PKMζ in subregions of the hippocampal formation of wild-type mice during LTP maintenance and spatial long-term memory storage. During LTP maintenance in hippocampal slices, PKMζ increases in the pyramidal cell body and stimulated dendritic layers of CA1 for at least 2 hr. During spatial memory storage, PKMζ increases in CA1 pyramidal cells for at least 1 month, paralleling the persistence of the memory. During the initial expression of the memory, we tagged principal cells with immediate-early gene Arc promoter-driven transcription of fluorescent proteins. The subset of memory-tagged CA1 cells selectively increases expression of PKMζ during memory storage, and the increase persists in dendritic compartments within stratum radiatum for 1 month, indicating long-term storage of information in the CA3-to-CA1 pathway. We conclude that persistent increases in PKMζ trace the molecular mechanism of LTP maintenance and thus the sites of information storage within brain circuitry during long-term memory.