Increased tubulin messenger RNA in the goldfish retina during optic nerve regeneration.

Axotomy induces profound morphological changes in the neuronal cell body 2,a,1°. Neurons whose axons lie within the central nervous system of higher vertebrates (intrinsic neurons) show little or no functional regenerative capability 4,8. However, many mammalian neurons whose axons lie outside the CNS, e.g., sensory and motor neuronsS, 15 and some intrinsic CNS neurons of lower vertebrates, such as teleosts and amphibia, can regenerate functional axons and re-establish normal synaptic fieldsT,9,11. This recuperative response of the perikaryon to axotomy provides a model for the study of regeneration as well as synaptogenesis and other events thought to underlie neuronal growth, recognition and plasticity. Regeneration of functional retinotectal fibers following optic nerve crush in goldfish is associated with a number of quantifiable biochemical changes in the retina, including increased nucleoside uptake and phosphorylation 1. There is also an enhanced labeling of cytoplasmic poly(A)-containing RNA 1 and of the microtubule protein tubulin 6. The enhanced radioisotopic labeling of goldfish retinal tubulin following optic nerve crush could be attributed either to its increased synthesis or decreased degradation. Since the former explanation could reflect regulation at the transcriptional or translational level and axotomy had resulted in enhanced labeling of poly(A)containing RNA, we investigated whether retinal poly(A)-RNA obtained following optic nerve crush was enriched in specific messenger RNAs, particularly that for tubulin. Translation of retinal poly(A)-containing RNA in a heterologous, cell-free protein synthesizing system, followed by SDS gel electrophoresis of the products, provided the necessary tools to detect the proposed changes in RNA populations. Cytoplasmic poly(A)-containing RNA preparations were isolated from both normal and from post-crush retinas, then incubated in a wheat germ protein synthesizing system. The protein labeling patterns from 4, 10 and 15 day post-crush incubations and their controls are shown in Fig. 1. A distinct increase in radioautographic density in the tubulin region of the gel was apparent in proteins translated