Neuronal activity-dependent membrane traffic at the neuromuscular junction

Area of Science:

• Neuroscience
• Molecular Biology
• Cell Biology

Background:

• Synaptic connections are dynamically modulated by neuronal activity throughout life.
• Understanding in vivo synaptic modifications requires advanced genetic tools.
• The tetanus toxin C-terminal fragment (TTC) possesses retrograde and transsynaptic transport capabilities.

Purpose of the Study:

• To develop and utilize a novel genetic tool for analyzing in vivo intracellular and transneuronal trafficking at the neuromuscular junction (NMJ).
• To investigate the dependence of synaptic traffic on presynaptic neuronal activity.

Main Methods:

• Intramuscular injection of a hybrid protein: beta-galactosidase fused to the nontoxic C-terminal fragment of tetanus toxin (beta-gal-TTC).
• In vivo analysis of protein transport within muscle and neuronal cells.
• Observation of protein localization at the postsynaptic side of the NMJ and within connected neurons.

Main Results:

• The beta-gal-TTC fusion protein demonstrated retrograde and transsynaptic transport, mirroring the holotoxin.
• Intracellular and transneuronal traffic at the NMJ were highly dependent on presynaptic neural cell activity.
• A directional membrane traffic concentrated the protein into the NMJ postsynaptic side in muscle.
• The probe was sorted to dendrites and subsequently to interconnected neurons, indicating transneuronal spread.

Conclusions:

• The developed beta-gal-TTC fusion protein serves as a sensitive reporter for presynaptic neuronal activity.
• This tool is highly valuable for studying morphological changes and plasticity at the neuromuscular junction in vivo.
• The findings elucidate mechanisms of intracellular and transneuronal transport at the synapse.