Intracellular RNA localization play pivotal roles in some developmental process including patterning of embryos, cell movement and cell fate determination. A neuron shows prominent polarity. The cell body typically protrudes short multiple dendrites with spines, and extends a long axon. The function of localized RNAs in the dendrites are extensively studied, and have been shown to be involved in various neuronal functions and genetic neural disorders. In contrast to dendritic RNAs axonal RNAs had been nearly neglected, but now it is getting accepted that some axonal RNAs are locally translated into proteins in vitro after external stimulations. There also several recent reports on the comprehensive identification of a number of axonal RNAs in vitro.
During the process of in situ hybridization screening of candidate genes involved in the tectum development of mid- to late-stage chick embryos, we detected more than twenty axonal RNAs in vivo. Interestingly, several of them are detected with probes for transcription factor-encoding RNAs. We also detected axonal signals with both antisense and sense probes for amyloid precursor protein (APP) mRNA. With DiI labeling we found that at least a subset of the cell bodies of the axons rich in the axonal RNAs may reside in the SGC of the tectum. We discuss the possible roles of the RNAs and also the candidate neurons expressing the axonal RNAs in the SGC.