Structural and functional maturation of presynaptic nerve endings under the control of transsynaptic signalling

Synapse assembly is the cellular mechanism that mediates the generation of physical con­nections between nerve cells and, thus, al­lows for the establishment of functional con­nectivity in the brain. The biogenesis of a syn­apse requires a set of highly coordinated mo­lecular events, ranging from initial forma­tion of adhesive contacts between an axon and a dendrite, followed by the recruitment and precise arrangement of synaptic organ­elles and proteins on both sides of the syn­aptic cleft, and culminating in the mainte­nance and remodelling of the exquisite archi­tecture of a differentiated, i.e. mature, synap­tic junction. Both the postsynaptic and the presynaptic compartment are thought to un­dergo stages of maturation that change and shape synaptic structure and function in a characteristic way. Recent evidence suggests that transsynaptic signalling, elicited by post­synaptic cell adhesion molecules, regulates the molecular events underlying presynap­tic maturation. Thus, synaptic cell adhesion molecules, apart from physically connecting nerve cells, emerge as coordinators of presyn­aptic and postsynaptic differentiation across the synaptic cleft.