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Target contact regulates GAP-43 and alpha-tubulin mRNA levels in regenerating retinal ganglion cells
P Bormann1, V M Zumsteg, L W Roth
1Department of Pharmacology, Biozentrum, University of Basel, Switzerland.
Abstract:
Axotomy of vertebrate neurons leads to the transient upregulation of GAP-43 and alpha-tubulin. In adult zebrafish retina, mRNA levels of both genes were increased in retinal ganglion cells after optic nerve lesion following a similar time course. At 5 days after crush, the mRNA level of GAP-43 was increased nearly 20 times, whereas a 6-fold increase was observed for alpha-tubulin. Subsequently, upon target reinnervation, mRNA levels of both genes were downregulated and were 2-fold higher than normal at 25 days after crush. Stretching the optic nerve that results in diffuse axonal lesions led to the expression of both genes in identical subsets of retinal ganglion cells. When regeneration was prevented by removing a piece of the optic nerve, mRNA levels remained elevated. Disruption of axonal transport by colchicine and vinblastine led to the induction of both genes in normal retina. Blocking electrical activity with tetrodotoxin had no effect. This indicates that retrogradely transported signals induced by target contact regulate GAP-43 and alpha-tubulin transcription. Furthermore, the joint regulation of GAP-43 and alpha-tubulin mRNA levels after different kinds of lesion suggests that a common pathway underlies the regulation of neuronal GAP-43 and alpha-tubulin gene expression. In contrast, distinct mechanisms may control the extent and maintenance of increased mRNA levels of these genes.
Insights
Neuronal injury upregulates GAP-43 and alpha-tubulin mRNA in zebrafish retinal ganglion cells. Target reinnervation downregulates these genes, suggesting injury-induced signals regulate their expression.
Area of Science:
- Neuroscience
- Molecular Biology
- Regenerative Medicine
Background:
- Axon injury in vertebrates triggers temporary increases in GAP-43 and alpha-tubulin.
- Retinal ganglion cells (RGCs) are crucial for vision, and understanding their response to injury is key for developing treatments.
Purpose of the Study:
- To investigate the regulation of GAP-43 and alpha-tubulin gene expression in adult zebrafish RGCs following optic nerve injury.
- To determine the role of axonal transport and target reinnervation in this process.
Main Methods:
- Optic nerve crush and stretch lesions in adult zebrafish.
- Quantitative analysis of GAP-43 and alpha-tubulin mRNA levels using techniques like quantitative PCR.
- Pharmacological disruption of axonal transport (colchicine, vinblastine) and neuronal activity (tetrodotoxin).
Main Results:
- Optic nerve lesion caused significant, time-dependent increases in GAP-43 and alpha-tubulin mRNA in RGCs.
- mRNA levels returned towards normal upon target reinnervation but remained elevated if regeneration was blocked.
- Disruption of axonal transport induced gene expression, while blocking electrical activity had no effect.
- GAP-43 and alpha-tubulin showed similar expression patterns, suggesting joint regulation.
Conclusions:
- Retrogradely transported signals, initiated by target contact after injury, regulate GAP-43 and alpha-tubulin transcription.
- A common regulatory pathway likely controls the induction of both genes after axonal injury.
- Distinct mechanisms may govern the magnitude and duration of elevated mRNA levels.
