Vertebrados

Mechanisms of Vertebrate Synaptogenesis
Annu. Rev. Neurosci. 2005.28:251-274. Downloaded from arjournals.annualreviews.org by Fondazione Centro San Raffaele del Monte Tabor on 01/19/06. For personal use only.

Clarissa L. Waites,1 Ann Marie Craig,2 and Craig C. Garner1
1

Department of Psychiatry and Behavioral Science, Nancy Pritzker Laboratory, Stanford University, Palo Alto, California,94304-5485; email: clarissa@stanford.edu, cgarner@stanford.edu Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri 63110-1093; email: acraig@pcg.wustl.edu

2

Annu. Rev. Neurosci. 2005. 28:251–74 doi: 10.1146/ annurev.neuro.27.070203.144336 Copyright c 2005 by Annual Reviews. All rights reserved First published online as a Review in Advance onMarch 17, 2005 0147-006X/05/07210251$20.00

Key Words
synapse, active zone, postsynaptic density, membrane trafficking, cytoskeleton

Abstract
The formation of synapses in the vertebrate central nervous system is a complex process that occurs over a protracted period of development. Recent work has begun to unravel the mysteries of synaptogenesis, demonstrating the existence of multiplemolecules that influence not only when and where synapses form but also synaptic specificity and stability. Some of these molecules act at a distance, steering axons to their correct receptive fields and promoting neuronal differentiation and maturation, whereas others act at the time of contact, providing positional information about the appropriateness of targets and/or inductive signals that triggerthe cascade of events leading to synapse formation. In addition, correlated synaptic activity provides critical information about the appropriateness of synaptic connections, thereby influencing synapse stability and elimination. Although synapse formation and elimination are hallmarks of early development, these processes are also fundamental to learning, memory, and cognition in the mature brain.251

Contents
INTRODUCTION . . . . . . . . . . . . . . . . . SPECIFICATION AND INDUCTION OF SYNAPSE FORMATION . . . . . . . . . . . . . . . . . . . Diffusible Target-Derived Factors Guiding Synapse Specificity . . . . Cell-Adhesion Molecules Guiding Synapse Specificity . . . . . . . . . . . . Inducers of Synapse Formation . . . . CELLULAR MECHANISMS OF SYNAPSE ASSEMBLY . . . . . . . . . .Membrane Trafficking in Presynaptic Assembly . . . . . . . . . . Membrane Trafficking in Postsynaptic Assembly . . . . . . . . . Synaptic Maturation . . . . . . . . . . . . . . ACTIVITY-DEPENDENT REGULATION OF SYNAPTOGENESIS . . . . . . . . . . . . Synapse Elimination . . . . . . . . . . . . . . Ubiquitin Regulation of Synapse Stability . . . . . . . . . . . . . . . . . . . . . . . CONCLUDING REMARKS .. . . . . . 252

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Axon: a long, thin neuronal process that carries electrical signals from the cell soma to presynaptic boutons Dendrite: a tapered neuronal process onto which presynaptic boutons form synapses. Signals from these dendritic synapses are propagated back to the cell soma, summed, and used to trigger an axonal action potentialSynapse: a site of contact between neurons where electrochemical signaling occurs

INTRODUCTION
The human brain is an amazingly complex organ composed of trillions of neurons. Every idea, emotion, and lofty thought we produce is created as a series of electrical and chemical signals transmitted through connected networks of neurons. Neurons transmit these signals to one another at specializedsites of contact called synapses. In the vertebrate nervous system, most neurons communicate via chemical synapses. As the name implies, chemical synapses function by converting electrical signals, in the form of action potentials racing down axons and invading presynaptic boutons, into chemical signals and then back to electrical impulses within the postsynaptic dendrite. Synapses perform this task...