Single β-Actin mRNA Detection in Neurons Reveals a Mechanism for Regulating Its Translatability

The physical manifestation of learning and memory formation in the brain can be expressed by strengthening or weakening of synaptic connections through morphological changes. Local actin remodeling underlies some forms of plasticity and may be facilitated by local beta-actin synthesis, but dynamic information is lacking. In this work, we use single-molecule in situ hybridization to demonstrate that dendritic beta-actin messenger RNA (mRNA) and ribosomes are in a masked, neuron-specific form. Chemically induced long-term potentiation prompts transient mRNA unmasking, which depends on factors active during synaptic activity. Ribosomes and single beta-actin mRNA motility increase after stimulation, indicative of release from complexes. Hence, the single-molecule assays we developed allow for the quantification of activity-induced unmasking and availability for active translation. Further, our work demonstrates that beta-actin mRNA and ribosomes are in a masked state that is alleviated by stimulation.