Abstract
BackgroundSemaphorins are known to play an important role in axon guidance and growth by triggering dynamic rearrangements of the actin cytoskeleton in the neuronal growth cone. Intriguingly, some of these guidance molecules are persistently expressed after axonal pathfinding and target recognition are completed. Although their function at these later stages is poorly understood, recent findings suggest a role for these proteins in regulating synaptic connections.ResultsHere we demonstrate that semaphorin 5B (Sema5B) regulates the elimination of synaptic connections in cultured hippocampal neurons. We show that Sema5B is proteolytically processed in neonatal brains and primary hippocampal cultures, resulting in the secretion of Sema5B fragments that include the biologically active semaphorin domain. Overexpression of full-length Sema5B in hippocampal neurons reduces synapse number while expression of a Sema5B construct lacking the semaphorin domain has no effect. Moreover, bath application with the proteolytically processed, secreted fragments containing the semaphorin domain of Sema5B, results in a rapid elimination of synaptic connections as demonstrated by time-lapse imaging. Conversely, depletion of endogenous Sema5B using RNA interference results in a significant increase in synapse number as well as a significant increase in the size of presynaptic and postsynaptic compartments.ConclusionOur results demonstrate that in addition to its role as a guidance cue, Sema5B regulates the development and maintenance of synapse size and number in hippocampal neurons. In addition, proteolytic cleavage of Sema5B results in the release of a potentially diffusible semaphorin domain that is a necessary component for its biological function in the regulation of synapse morphology.
Highlights
Semaphorins are known to play an important role in axon guidance and growth by triggering dynamic rearrangements of the actin cytoskeleton in the neuronal growth cone
semaphorin 5B (Sema5B) antibody Antibodies were generated against the N-terminus of full length Sema5B along a region that showed the least amino acid homology with other semaphorins including Sema5A (Figure 1a)
A 150 kDa Sema5B band was absent in postnatal day 1 (P1) cortical or hippocampal lysates, but several smaller bands were apparent indicating that the majority of Sema5B is proteolytically processed (Figure 1d)
Summary
Semaphorins are known to play an important role in axon guidance and growth by triggering dynamic rearrangements of the actin cytoskeleton in the neuronal growth cone. Some of these guidance molecules are persistently expressed after axonal pathfinding and target recognition are completed. Their function at these later stages is poorly understood, recent findings suggest a role for these proteins in regulating synaptic connections. Synaptic networks are refined through the elimination of excessive or inappropriate synapses that have initially been formed [1,2,3]. In addition to these early refinement events, the assembly and disassembly of synapses persists (page number not for citation purposes). Semaphorins typically confer their inhibitory activity through a conserved 500 amino acid 'sema' domain [9], while a variety of alternative functions are associated with their varied C-terminal domains
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
