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A Kimberley McAllister

Publications and source records attributed to A Kimberley McAllister.

14 recordsLinked to original sources
PubMed2006

The dynamic distribution of TrkB receptors before, during, and after synapse formation between cortical neurons.

Although brain-derived neurotrophic factor (BDNF) potently regulates neuronal connectivity in the developing CNS, the mechanism by which BDNF influences the formation and/or maintenance of glutamatergic synapses remains unknown. Details about the subcellular localization of the BDNF receptor, TrkB, relative to synaptic and nonsynaptic proteins on excitatory neurons should provide insight into how BDNF might exert its effects during synapse formation. Here, we investigated the subcellular localization of tyrosine kinase receptor B (TrkB) relative to synaptic vesicle-associated proteins and NMDA receptors using immunocytochemistry, confocal microscopy, and time-lapse imaging in dissociated cultures of cortical neurons before, during, and after the peak of synapse formation. We find that TrkB is present in puncta on the surface and intracellularly in both dendrites and axons throughout development. Before synapse formation, some TrkB puncta in dendrites colocalize with NMDA receptors, and almost all TrkB puncta in axons colocalize with synaptic vesicle proteins. Clusters of TrkB fused to the enhanced green fluorescent protein (TrkB-EGFP) are highly mobile in both axons and dendrites. In axons, TrkB-EGFP dynamics are almost identical to vesicle-associated protein (VAMP2-EGFP), and these proteins are often transported together. Finally, surface TrkB is found in structures that actively participate in synapse formation: axonal growth cones and dendritic filopodia. Over time, surface TrkB becomes enriched at glutamatergic synapses, which contain both catalytic and truncated TrkB. These results suggest that TrkB is in the right place at the right time to play a direct role in the formation of glutamatergic synapses between cortical neurons.

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PubMed2006

Formation of presynaptic terminals at predefined sites along axons.

What determines where synapses will form along an axon or how proteins are deposited at nascent synapses remains unknown. Here, we show that the initial formation of presynaptic terminals occurs preferentially at predefined sites within the axons of cortical neurons. Time-lapse imaging of synaptic vesicle protein transport vesicles (STVs) indicates that STVs pause repeatedly at these sites, even in the absence of neuronal or glial contact. Contact with a neuroligin-expressing non-neuronal cell induces formation of presynaptic terminals specifically at these STV pause sites. Remarkably, formation of stable contacts with dendritic filopodia also occurs selectively at STV pause sites. Although it is not yet known which molecules comprise the predefined sites, STV pausing is regulated by cues that affect synaptogenesis. Overall, these data are consistent with the hypothesis that regulation of STV pausing might be an important mechanism for accumulation of presynaptic proteins at nascent synapses and support a new model in which many en passant synapses form specifically at predefined sites in young axons.

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PubMed2004

Cycling of NMDA receptors during trafficking in neurons before synapse formation.

The trafficking of glutamate receptors in neurons is of the utmost importance for synapse formation and synaptic plasticity. Recently, we demonstrated that both NMDA and AMPA receptors reside in mobile transport packets that are recruited rapidly and independently to nascent synapses. Here, we show that a large proportion of the glutamate receptor clusters in young cortical neurons are present on the surface of dendrites before synapses are formed and these surface-exposed transport packets are mobile. Exocytosis of glutamate receptors to the dendritic surface occurs via a SNARE [soluble n-ethylmaleimide-sensitive factor attachment protein (SNAP) receptor]-dependent SNAP-23-mediated mechanism. Endocytosis occurs rapidly after surface exposure; >50% of surface-labeled NMDA receptors (NMDARs) are endocytosed within 5 min. NMDARs are transported along microtubules on large tubulovesicular organelles, as indicated by immunoelectron microscopy, and are associated with EEA1 (early endosomal antigen 1) and SAP102 (synapse-associated protein 102), as indicated by immunocytochemistry. Most surprisingly, a large proportion of these transport packets cycle through the dendritic plasma membrane before synapse formation. These results suggest a novel model in which NMDARs cycle with the plasma membrane during pauses of movement along microtubules while trafficking.

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PubMed2003

Mobility and cycling of synaptic protein-containing vesicles in axonal growth cone filopodia.

The spatial distribution and coordination of vesicular dynamics within growth cones are poorly understood. It has long been thought that membranous organelles are concentrated in the central regions of growth cones and excluded from filopodia; this view has dramatically shaped conceptual models of the cellular mechanisms of axonal growth and presynaptic terminal formation. To begin to test these models, we studied membrane dynamics within axonal growth cones of living rat cortical neurons. We demonstrate that growth cone filopodia contain vesicles that transport synaptic vesicle proteins bidirectionally along filopodia and fuse with the filopodial surface in response to focal stimulation, allowing for both local secretion of vesicular contents and rapid changes in the plasma membrane composition of individual filopodia. Our results suggest a new model in which growth cone filopodia are actively involved in both emitting and responding to local signals related to axon growth and early synapse formation.

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PubMed2002

Spatially restricted actions of BDNF.

In this issue of Neuron, Zhang and Poo present evidence for localized BDNF-induced synaptic potentiation that is accompanied by spatially restricted calcium influx and requires local axonal protein synthesis. These results are consistent with a synapse-specific role for BDNF and provide a potentially novel way to think about cellular mechanisms for potentiation of neurotransmitter release.

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PubMed2002

BDNF.

Explore the source record for details and available documents.

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PubMed2002

Conserved cues for axon and dendrite growth in the developing cortex.

The cellular and molecular mechanisms that guide axonal and dendritic differentiation in the cerebral cortex are just beginning to be defined. Many of the molecular signals that guide axons also, and sometimes simultaneously, influence dendritic growth. Whitford et al. (2002 [this issue of Neuron]) demonstrate that in addition to their roles in axon guidance and cell migration cue, Slit proteins can also regulate dendritic growth.

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PubMed2002

Neurotrophins and cortical development.

The mammalian cerebral cortex requires the proper formation of exquisitely precise circuits to function correctly. These neuronal circuits are assembled during development by the formation of synaptic connections between hundreds of thousands of differentiating neurons. Although the development of the cerebral cortex has been well described anatomically, the cellular and molecular mechanisms that guide neuronal differentiation and formation of connections are just beginning to be understood. Moreover, despite evidence that coordinated patterns of activity underlie reorganization of brain circuits during critical periods of development, the molecular signals that translate activity into structural and functional changes in connections remain unknown. Recently, the neurotrophins have emerged as attractive candidates not only for regulating neuronal differentiation in the developing brain, but also for mediating activity-dependent synaptic plasticity. The neurotrophins meet many of the criteria required for molecular signals involved in neuronal differentiation and plasticity. They are present in the cerebral cortex during development and their expression is regulated by synaptic activity. In turn, the neurotrophins themselves strongly influence both short-term synaptic plasticity and long-term potentiation and depression. In addition to their functional effects, the neurotrophins also profoundly regulate the structural changes that underlie axonal and dendritic differentiation. Finally, the neurotrophins have been implicated in mediating synaptic competition required for activity-dependent plasticity during the critical period. This chapter presents and discusses the rapidly accumulating evidence that the neurotrophins are critical for neuronal differentiation and that they may be involved in activity-dependent synaptic refinement in the developing cerebral cortex.

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PubMed2002

Techniques for gene transfer into neurons.

To illuminate the function of the thousands of genes that make up the complexity of the nervous system, it is critical to be able to introduce and express DNA in neurons. Over the past two decades, many gene transfer methods have been developed, including viral vectors, liposomes and electroporation. Although the perfect gene transfer technique for every application has not yet been developed, recent technical advances have facilitated the ease of neuronal gene transfer and have increased the accessibility of these techniques to all laboratories. In order to select a transfection method for any particular experiment, the specific advantages and disadvantages of each technique must be considered.

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PubMed2002

Rapid recruitment of NMDA receptor transport packets to nascent synapses.

Although many of the molecules involved in synaptogenesis have been identified, the sequence and kinetics of synapse assembly in the central nervous system (CNS) remain largely unknown. We used simultaneous time-lapse imaging of fluorescent glutamate receptor subunits and presynaptic proteins in rat cortical neurons in vitro to determine the dynamics and time course of N-methyl-D-aspartate receptor (NMDAR) recruitment to nascent synapses. We found that both NMDA and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) subunits are present in mobile transport packets in neurons before and during synaptogenesis. NMDAR transport packets are more mobile than AMPAR subunits, moving along microtubules at about 4 microm/min, and are recruited to sites of axodendritic contact within minutes. Whereas NMDAR recruitment to new synapses can be either concurrent with or independent of the protein PSD-95, AMPARs are recruited with a slower time course. Thus, glutamatergic synapses can form rapidly by the sequential delivery of modular transport packets containing glutamate receptors.

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