Transport of BC1 RNA in hypothalamo-neurohypophyseal axons

Ample evidence indicates that in nerve cells, several individual proteins are locally synthesized in postsynaptic domains in dendrites. By contrast, axonal terminals, at least in mammals, are generally thought to lack protein synthetic capacity. However, axonal nerve endings of the hypothalamo-neurohypophyseal tract have recently been shown to contain mRNAs encoding vasopressin, oxytocin, dynorphin, and neurofilament. In this report, we identify BC1 RNA, a small RNA polymerase III transcript that is specifically expressed in neurons, in hypothalamo-neurohypophyseal axons. BC1 RNA has previously been shown to be located in somatic and dendritic domains of various types of neurons in the rat nervous system. Here we present evidence to show that BC 1 RNA, like several neuropeptide mRNAs, is axonally transported from magnocellular hypothalamic neurons to neurosecretory nerve endings in the posterior pituitary. BC1 RNA, which has been reported to be a component of a ribonucleoprotein particle, is thus colocalized with dendritic mRNAs in dendritic domains and with axonal mRNAs in axonal domains, respectively. Such colocalization is indicative of functional interactions of BC1 RNA with those mRNAs that are targeted to extrasomatic domains of nerve cells.