Axonal transport of 4S RNA in the chick optic system

The axonal transport of tRNA has been investigated in the chick optic system. Chicks were injected with [3H]uridine intraocularly or intracranially and the RNA of the retina, nerve complex, and tecta separated by polyacrylamide gel electrophoresis and then counted. The ratio of tRNA to rRNA specific activities increased with time in both the nerve complex and contralateral tectum. The ratio increased more rapidly in the nerve complex than the tectum. However, no increase was observed in the case of intracranially injected animals. This is consistent with the axonal flow of tRNA. When [methyl-3H]methionine was used as precursor, the preferential labeling of 4S RNA to rRNA which resulted more clearly showed a transport of 4S RNA from the retinal cells to the tectum. In conclusion, it was found that about 40% of the radioactive RNA observed within the optic tectum 4 days after an intraocular injection of [3H]uridine was accounted for by 4S RNA which has flowed from the retina. However, the migration of a methylated RNA molecule of size 4S, but unrelated to rRNA, cannot be entirely eliminated.