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Bidirectional modulation of synaptic functions by Eph/ephrin signaling

Summary: Bidirectional modulation of synaptic functions by
Eph/ephrin signaling
Ru¨diger Klein
Ephrin ligands and their cognate Eph receptors guide axons during neural development and regulate synapse formation and neuronal
plasticity in the adult. Because ephrins are tethered to the plasma membrane and possess reverse signaling properties, the
Eph-ephrin system can function in a bidirectional, contact-mediated fashion between two opposing cells. Eph receptors expressed
on dendrites are activated by ephrins (on axons or on astrocytes) and regulate spine and synapse formation. They also participate in
activity-induced long-term changes in synaptic strength such as long-term potentiation (LTP). When expressed on axon terminals,
ephrins promote presynaptic differentiation and enhance neurotransmitter release, thereby supporting presynaptic forms of LTP. In
some cases, Eph receptors can simply act as ligands for ephrins without any requirement for Eph receptor signaling, suggesting that
the system does not always function bidirectionally.
After axons have reached their target field, short-range interactions
between axons and target cells are required for specific synapse
formation. This process involves structural modifications in both
axon terminals and dendrites. Bidirectional signaling systems in
which one component signals into the axon terminal and the other
component signals into the dendrite are particularly suited for regulat-
ing this process. Candidate signaling systems are ephrin/Eph receptors,
neuroligin/neurexins, SynCAMs and cadherins1. The same bidirec-
tional signals may later participate in activity-dependent structural


Source: Alford, Simon - Department of Biological Sciences, University of Illinois at Chicago


Collections: Biology and Medicine