Neurexins: molecular codes for shaping neuronal synapses
Andrea M. Gomez, Lisa Traunmüller, Peter Scheiffele
Abstract
Nervous systems represent remarkable examples of a highly organized tissue with an abundance of specialized cells in an intricate structure. During development, neuronal connectivity arises from a series of steps, including cell specification, migration, targeted growth, synapse formation and remodelling. Spontaneous activity and sensory experience propagated through the developing networks play a significant role in organizing aspects of neuronal wiring. However, many fundamental steps of neuronal morphogenesis and synapse formation proceed normally even in the absence of neurotransmission Thus, genetically encoded programmes are thought to orchestrate key aspects of the timing and dynamics of neuronal growth and nervous system wiring Cell surface adhesion and signalling molecules significantly contribute to all of these developmental steps. Thus, each neuronal cell type carries an array of cues linked to cellular origin and cell fate that are integral to its developmental specification. Although signalling processes, neuronal activity and disease states may shift these codes, there are constraints that restrict this plasticity, thereby maintaining cell type-specific properties. One critical and extensively studied process in nervous system development is the selective growth and targeting of neurites, which encompasses axon guidance and synaptic specificity The present Review aims to discuss a second key aspect of neuronal wiring: the molecular principles of neuronal synapse formation and the specification of synapse function. We will use the Neurexin family, one class of cell adhesion molecules, to illustrate the fundamental principles of this process that likely apply to many other adhesion systems operating at neuronal synapses.