@article {140, title = {Non-cell-autonomous mechanism of activity-dependent neurotransmitter switching.}, journal = {Neuron}, volume = {82}, year = {2014}, month = {2014 Jun 4}, pages = {1004-16}, abstract = {

Activity-dependent neurotransmitter switching engages genetic programs regulating transmitter synthesis, but the mechanism by which activity is transduced is unknown. We suppressed activity in single neurons in the embryonic spinal cord to determine whether glutamate-gamma-aminobutyric acid (GABA) switching is cell autonomous. Transmitter respecification did not occur, suggesting that it is homeostatically regulated by the level of activity in surrounding neurons. Graded increase in the number of silenced neurons in cultures led to graded decrease in the number of neurons expressing GABA, supporting non-cell-autonomous transmitter switching. We found that brain-derived neurotrophic factor (BDNF) is expressed in the spinal cord during the period of transmitter respecification and that spike activity causes release of BDNF. Activation of TrkB receptors triggers a signaling cascade involving JNK-mediated activation of cJun that regulates tlx3, a glutamate/GABA selector gene, accounting for calcium-spike BDNF-dependent transmitter switching. Our findings identify a molecular mechanism for activity-dependent respecification of neurotransmitter phenotype in developing spinal neurons.

}, keywords = {Animals, Brain-Derived Neurotrophic Factor, Calcium, Cells, Cultured, Female, gamma-Aminobutyric Acid, Glutamic Acid, JNK Mitogen-Activated Protein Kinases, Neurons, Phosphorylation, Proto-Oncogene Proteins c-jun, Signal Transduction, Spinal Cord, Xenopus laevis}, issn = {1097-4199}, doi = {10.1016/j.neuron.2014.04.029}, author = {Guemez-Gamboa, Alicia and Xu, Lin and Meng, Da and Spitzer, Nicholas C} } @article {137, title = {Spatial and temporal second messenger codes for growth cone turning.}, journal = {Proc Natl Acad Sci U S A}, volume = {108}, year = {2011}, month = {2011 Aug 16}, pages = {13776-81}, abstract = {

Cyclic AMP (cAMP) and calcium are ubiquitous, interdependent second messengers that regulate a wide range of cellular processes. During development of neuronal networks they are critical for the first step of circuit formation, transducing signals required for axon pathfinding. Surprisingly, the spatial and temporal cAMP and calcium codes used by axon guidance molecules are unknown. Here, we identify characteristics of cAMP and calcium transients generated in growth cones during Netrin-1-dependent axon guidance. In filopodia, Netrin-1-dependent Deleted in Colorectal Cancer (DCC) receptor activation induces a transient increase in cAMP that causes a brief increase in calcium transient frequency. In contrast, activation of DCC in growth cone centers leads to a transient calcium-dependent cAMP increase and a sustained increase in frequency of calcium transients. We show that filopodial cAMP transients regulate spinal axon guidance in vitro and commissural axon pathfinding in vivo. These growth cone codes provide a basis for selective activation of specific downstream effectors.

}, keywords = {Animals, Axons, Calcium, Cells, Cultured, Cyclic AMP, Growth Cones, Nerve Growth Factors, Neurons, Pseudopodia, Receptors, Cell Surface, Second Messenger Systems, Tumor Suppressor Proteins, Xenopus}, issn = {1091-6490}, doi = {10.1073/pnas.1100247108}, author = {Nicol, Xavier and Hong, Kwan Pyo and Spitzer, Nicholas C} } @article {136, title = {Activity-dependent expression of Lmx1b regulates specification of serotonergic neurons modulating swimming behavior.}, journal = {Neuron}, volume = {67}, year = {2010}, month = {2010 Jul 29}, pages = {321-34}, abstract = {

Genetic programs, environmental factors, and electrical activity interact to drive the maturation of the brain. Although the cascade of transcription factors that leads to specification of the serotonergic phenotype has been well characterized, its interactions with electrical activity are not known. Here we show that spontaneous calcium spike activity in the hindbrain of developing Xenopus laevis larvae modulates the specification of serotonergic neurons via regulation of expression of the Lmx1b transcription factor. Activity acts downstream of Nkx2.2 but upstream of Lmx1b, leading to regulation of the serotonergic phenotype. Using global manipulation of activity and targeted alteration of Lmx1b expression, we also demonstrate that changes in the number of serotonergic neurons change larval swimming behavior. The results link activity-dependent regulation of a transcription factor to transmitter specification and altered behavior.

}, keywords = {Action Potentials, Animals, Behavior, Animal, Bromodeoxyuridine, Calcium, Electroporation, Embryo, Nonmammalian, gamma-Aminobutyric Acid, Gene Expression Regulation, Developmental, Green Fluorescent Proteins, Homeodomain Proteins, Membrane Potentials, Neurons, Otx Transcription Factors, Potassium Channels, Inwardly Rectifying, Raphe Nuclei, RNA, Messenger, Serotonin, Sodium Channels, Statistics, Nonparametric, Swimming, Transcription Factors, Tryptophan Hydroxylase, Xenopus laevis, Xenopus Proteins}, issn = {1097-4199}, doi = {10.1016/j.neuron.2010.06.006}, author = {Demarque, Micha{\"e}l and Spitzer, Nicholas C} } @article {135, title = {cJun integrates calcium activity and tlx3 expression to regulate neurotransmitter specification.}, journal = {Nat Neurosci}, volume = {13}, year = {2010}, month = {2010 Aug}, pages = {944-50}, abstract = {

Neuronal differentiation is accomplished through cascades of intrinsic genetic factors initiated in neuronal progenitors by external gradients of morphogens. Activity has been thought to be important only late in development, but recent evidence suggests that activity also regulates early neuronal differentiation. Activity in post-mitotic neurons before synapse formation can regulate phenotypic specification, including neurotransmitter choice, but the mechanisms are not clear. We identified a mechanism that links endogenous calcium spike activity with an intrinsic genetic pathway to specify neurotransmitter choice in neurons in the dorsal embryonic spinal cord of Xenopus tropicalis. Early activity modulated transcription of the GABAergic/glutamatergic selection gene tlx3 through a variant cAMP response element (CRE) in its promoter. The cJun transcription factor bound to this CRE site, modulated transcription and regulated neurotransmitter phenotype via its transactivation domain. Calcium signaled through cJun N-terminal phosphorylation, which integrated activity-dependent and intrinsic neurotransmitter specification. This mechanism provides a basis for early activity to regulate genetic pathways at critical decision points, switching the phenotype of developing neurons.

}, keywords = {Animals, Base Sequence, Calcium, Calcium Signaling, Electrophoretic Mobility Shift Assay, Gene Expression, Gene Expression Regulation, Developmental, Homeodomain Proteins, Immunohistochemistry, In Situ Hybridization, Molecular Sequence Data, Neurogenesis, Neurons, Neurotransmitter Agents, Promoter Regions, Genetic, Proto-Oncogene Proteins c-jun, Response Elements, Reverse Transcriptase Polymerase Chain Reaction, Xenopus, Xenopus Proteins}, issn = {1546-1726}, doi = {10.1038/nn.2582}, author = {Marek, Kurt W and Kurtz, Lisa M and Spitzer, Nicholas C} } @article {132, title = {Embryonically expressed GABA and glutamate drive electrical activity regulating neurotransmitter specification.}, journal = {J Neurosci}, volume = {28}, year = {2008}, month = {2008 Apr 30}, pages = {4777-84}, abstract = {

Neurotransmitter signaling in the mature nervous system is well understood, but the functions of transmitters in the immature nervous system are less clear. Although transmitters released during embryogenesis regulate neuronal proliferation and migration, little is known about their role in regulating early neuronal differentiation. Here, we show that GABA and glutamate drive calcium-dependent embryonic electrical activity that regulates transmitter specification. The number of neurons expressing different transmitters changes when GABA or glutamate signaling is blocked chronically, either using morpholinos to knock down transmitter-synthetic enzymes or applying pharmacological receptor antagonists during a sensitive period of development. We find that calcium spikes are triggered by metabotropic GABA and glutamate receptors, which engage protein kinases A and C. The results reveal a novel role for embryonically expressed neurotransmitters.

}, keywords = {Animals, Antigens, CD57, Calcium, Choline O-Acetyltransferase, Embryo, Nonmammalian, Enzyme Inhibitors, Excitatory Amino Acid Antagonists, GABA Antagonists, gamma-Aminobutyric Acid, Gene Expression Regulation, Developmental, Glutamate Decarboxylase, Glutamic Acid, Health Services Research, Larva, Morpholines, Neurons, Phosphoserine, Receptors, GABA, Receptors, Glutamate, Synapses, Vesicular Glutamate Transport Proteins, Xenopus}, issn = {1529-2401}, doi = {10.1523/JNEUROSCI.4873-07.2008}, author = {Root, Cory M and Vel{\'a}zquez-Ulloa, Norma A and Monsalve, Gabriela C and Minakova, Elena and Spitzer, Nicholas C} } @article {131, title = {Activity-dependent neurotransmitter-receptor matching at the neuromuscular junction.}, journal = {Proc Natl Acad Sci U S A}, volume = {104}, year = {2007}, month = {2007 Jan 2}, pages = {335-40}, abstract = {

Signaling in the nervous system requires matching of neurotransmitter receptors with cognate neurotransmitters at synapses. The vertebrate neuromuscular junction is the best studied cholinergic synapse, but the mechanisms by which acetylcholine is matched with acetylcholine receptors are not fully understood. Because alterations in neuronal calcium spike activity alter transmitter specification in embryonic spinal neurons, we hypothesized that receptor expression in postsynaptic cells follows changes in transmitter expression to achieve this specific match. We find that embryonic vertebrate striated muscle cells normally express receptors for glutamate, GABA, and glycine as well as for acetylcholine. As maturation progresses, acetylcholine receptor expression prevails. Receptor selection is altered when early neuronal calcium-dependent activity is perturbed, and remaining receptor populations parallel changes in transmitter phenotype. In these cases, glutamatergic, GABAergic, and glycinergic synaptic currents are recorded from muscle cells, demonstrating that activity regulates matching of transmitters and their receptors in the assembly of functional synapses.

}, keywords = {Animals, Calcium, Gene Expression Regulation, Developmental, Muscle, Skeletal, Neuromuscular Junction, Neurotransmitter Agents, Receptors, Neurotransmitter, Spinal Cord, Synapses, Xenopus}, issn = {0027-8424}, doi = {10.1073/pnas.0607450104}, author = {Borodinsky, Laura N and Spitzer, Nicholas C} } @article {130, title = {Activity-dependent homeostatic specification of transmitter expression in embryonic neurons.}, journal = {Nature}, volume = {429}, year = {2004}, month = {2004 Jun 3}, pages = {523-30}, abstract = {

Neurotransmitters are essential for interneuronal signalling, and the specification of appropriate transmitters in differentiating neurons has been related to intrinsic neuronal identity and to extrinsic signalling proteins. Here we show that altering the distinct patterns of Ca2+ spike activity spontaneously generated by different classes of embryonic spinal neurons in vivo changes the transmitter that neurons express without affecting the expression of markers of cell identity. Regulation seems to be homeostatic: suppression of activity leads to an increased number of neurons expressing excitatory transmitters and a decreased number of neurons expressing inhibitory transmitters; the reverse occurs when activity is enhanced. The imposition of specific spike frequencies in vitro does not affect labels of cell identity but again specifies the expression of transmitters that are inappropriate for the markers they express, during an early critical period. The results identify a new role of patterned activity in development of the central nervous system.

}, keywords = {Action Potentials, Animals, Calcium, Calcium Signaling, Cell Differentiation, Cells, Cultured, Gene Expression Regulation, Homeostasis, Humans, Neurons, Neurotransmitter Agents, Organ Specificity, Phenotype, Potassium Channels, Inwardly Rectifying, Rats, Sodium Channels, Spinal Cord, Xenopus laevis}, issn = {1476-4687}, doi = {10.1038/nature02518}, author = {Borodinsky, Laura N and Root, Cory M and Cronin, Julia A and Sann, Sharon B and Gu, Xiaonan and Spitzer, Nicholas C} }