Target interaction regulates distribution and stability of specific mRNAs.

Several factors regulate export of mRNAs from neuronal cell bodies. Using in situ hybridization and RT-PCR, we examined how target interaction influences the distribution of mRNAs expressed in sensory neurons (SNs) of Aplysia maintained in cell culture. Interaction with a synaptic target has two effects on the distribution of mRNA encoding an SN-specific peptide, sensorin: the target affects the accumulation of sensorin mRNA at the axon hillock and the stability of sensorin mRNA exported to distal sites. Synapse formation with motor neuron L7 results in the accumulation of high levels of sensorin mRNA in the axon hillock of the SN and in SN neurites contacting L7. SNs cultured alone or in contact with motor neuron L11, with which no synapses form, show a more uniform distribution of sensorin mRNA in the cytoplasm of the SN cell body, with little expression in neurites. Contact with L7 or L11 had little or no effect on the distribution of two other mRNAs in the cytoplasm of SN cell bodies. Sensorin mRNA exported to SN neurites after 1 d in culture is more stable when the SN contacts L7 compared with SN neurites that contact L11. After removal of the SN cell body, the amounts of sensorin mRNA already exported to the neurites are greater when neurites contact L7 compared with neurites in contact with L11. The results indicate that target interaction and synapse formation regulate both the accumulations of specific mRNAs destined for export and their stability at distant sites.