ACTIVITY-DEPENDENT REGULATION OF DENDRITIC BC1 RNA IN HIPPOCAMPAL-NEURONS IN CULTURE

Several neuronal RNAs have been identified in dendrites, and it has be en suggested that the dendritic location of these RNAs may be relevant to the spatiotemporal regulation of mosaic postsynaptic protein reper toires through transsynaptic activity. Such regulation would require t hat dendritic RNAs themselves, or at least some of them, be subject to physiological control. We have therefore examined the functional regu lation of somatodendritic expression levels of dendritic BC1 RNA in hi ppocampal neurons in culture. BC1 RNA, an RNA polymerase III transcrip t that is a component of a ribonucleoprotein particle, became first de tectable in somatodendritic domains of developing hippocampal neurons at times of initial synapse formation. BC1 RNA was identified only in such neurons that had established synapses on cell bodies and/or devel oping dendritic arbors. When synaptic contact formation was initiated later in low-density cultures, BC1 expression was coordinately delayed . Inhibition of neuronal activity in hippocampal neurons resulted in a substantial but reversible reduction of somatodendritic BC1 expressio n. We conclude that expression of BC1 RNA in somatic and dendritic dom ains of hippocampal neurons is regulated in development, and is depend ent upon neuronal activity. These results establish (for the first tim e to our knowledge) that an RNA polymerase III transcript can be subje ct to control through physiological activity in nerve cells.