TRANSPORT OF BC1 RNA IN HYPOTHALAMONEUROHYPOPHYSEAL AXONS

Ample evidence indicates that in nerve cells, several individual prote ins are locally synthesized in postsynaptic domains in dendrites. By c ontrast, axonal terminals, at least in mammals, are generally thought to lack protein synthetic capacity. However, axonal nerve endings of t he hypothalamo-neurohypophyseal tract have recently been shown to cont ain mRNAs encoding vasopressin, oxytocin, dynorphin, and neurofilament . In this report, we identify BC1 RNA, a small RNA polymerase III tran script that is specifically expressed in neurons, in hypothalamo-neuro hypophyseal axons. BC1 RNA has previously been shown to be located in somatic and dendritic domains of various types of neurons in the rat n ervous system. Here we present evidence to show that BC1 RNA, like sev eral neuropeptide mRNAs, is axonally transported from magnocellular hy pothalamic neurons to neurosecretory nerve endings in the posterior pi tuitary. BC1 RNA, which has been reported to be a component of a ribon ucleoprotein particle, is thus colocalized with dendritic mRNAs in den dritic domains and with axonal mRNAs in axonal domains, respectively. Such colocalization is indicative of functional interactions of BC1 RN A with those mRNAs that are targeted to extrasomatic domains of nerve cells.