Stages of synapse development defined by dependence on F-actin

Area of Science:

• Neuroscience
• Cell Biology
• Synaptic Plasticity

Background:

• The role of actin filaments (F-actin) in central nervous system (CNS) synapse assembly has been speculated but not experimentally proven.
• Understanding F-actin's function is key to comprehending synapse formation, maturation, and stability.

Purpose of the Study:

• To experimentally demonstrate the requirement of F-actin for synapse formation and maturation in cultured hippocampal neurons.
• To investigate the dynamic relationship between F-actin stability and synapse maturation over time.

Main Methods:

• Utilized cultured hippocampal neurons.
• Employed latrunculin A, an actin depolymerizing agent, to disrupt F-actin.
• Assessed synapse formation and maturation using markers like synaptophysin, synaptic vesicle recycling (FM4-64), and ultrastructure.
• Examined the presence of scaffolding proteins (Bassoon, PSD-95 family) over time.

Main Results:

• Actin depolymerization in the first week led to a near-complete loss of synapses, affecting vesicle clusters and recycling.
• In the second week, synapses became less dependent on F-actin, though vesicle anchoring remained partially reliant.
• Synapse dependence on F-actin decreased as presynaptic (Bassoon) and postsynaptic (PSD-95) scaffolding proteins were acquired.
• Increased neuronal activity correlated with stabilized F-actin and synaptic proteins, linking active synapses to actin and synapse stability.

Conclusions:

• F-actin is essential for the development and maintenance of young CNS synapses.
• F-actin's dynamic nature and regulation suggest it is a key target for signals controlling synapse maintenance or elimination.
• Synapse stability is closely associated with the stability of F-actin and associated scaffolding proteins.