Protein degradation is critical for brain function through processes that remain incompletely understood. Here, we investigated the in vivo function of the 20S neuronal membrane proteasome (NMP) in the brain of Xenopus laevis tadpoles. With biochemistry, immunohistochemistry, and electron microscopy, we demonstrated that NMPs are conserved in the tadpole brain and preferentially degrade neuronal activity–induced newly synthesized proteins in vivo. Using in vivo calcium imaging in the optic tectum, we showed that acute NMP inhibition rapidly increased spontaneous neuronal activity, resulting in hypersynchronization across tectal neurons. At the circuit level, inhibiting NMPs abolished learning-dependent improvement in visuomotor behavior in live animals and caused a significant deterioration in basal behavioral performance following visual training with enhanced visual experience. Our data provide in vivo characterization of NMP functions in the vertebrate nervous system and suggest that NMP-mediated degradation of activity-induced nascent proteins may serve as a homeostatic modulatory mechanism in neurons that is critical for regulating neuronal activity and experience-dependent circuit plasticity.

Protein degradation is critical for brain function through processes that remain poorly understood. Here we investigated the in vivo function of a recently reported neuronal membrane-associated proteasome (NMP) in the brain of Xenopus laevis tadpoles. We demonstrated that NMPs are present in the tadpole brain with biochemistry and electron microscopy, and showed that they actively degrade neuronal activity-induced nascent proteins. Using in vivo calcium imaging in the optic tectum, we showed that acute inhibition of NMP function rapidly increased spontaneous neuronal activity, resulting in hyper-synchronization among tectal neurons. At the circuit level, inhibiting NMPs abolished learning-dependent improvement in a visuomotor behavior paradigm in live animals. Our data provide the first in vivo characterization of NMP functions in the vertebrate nervous system and suggest that NMP-mediated degradation of activity-induced nascent proteins may serve as a homeostatic modulatory mechanism in neurons that is critical for regulating neuronal activity and experience-dependent circuit plasticity.