In an interesting additional approach, they use the recently developed TRAP technique (Heiman et al., 2008) to show that lamin B2 mRNA is associated with ribosomes in RGC axons in vivo. In this method, animals are generated expressing GFP-tagged ribosomes, then the ribosomes are immunoprecipitated

using anti-GFP antibodies, and associated RNAs are identified. Here, the authors created Xenopus tadpoles in which GFP-tagged ribosomes were only expressed in a transplanted eye. These RGC axons innervated the host tectum, ensuring that tectal lysates would contain GFP-tagged ribosomes originating exclusively from RGC axons. Anti-GFP immunoprecipitation demonstrated the association of lamin B2 mRNA with ribosomes in Ulixertinib ic50 retinal axons, providing evidence that lamin B2 is locally translated in these axons in vivo. Having demonstrated that lamin B2 is produced in RGC axons, Yoon et al. then examined its function there in vivo. First, they knocked down lamin B2 in the eye by antisense morpholino and found that RGC axons degenerated after they reached the tectum, while their cell bodies survived. This shows that lamin B2 is essential for RGC axon maintenance in vivo. They then asked whether its role in axon maintenance relied on its presence in the axon rather than in the nucleus. Consistent with this hypothesis, the lamin B2 knockdown phenotype

could be rescued by overexpressing a mutant form of lamin B2 that cannot enter the nucleus. Moreover, knockdown of lamin B2 by applying morpholino Rebamipide Selleck Anti-diabetic Compound Library specifically to the tectum, presumably affecting RGC axons but not their cell bodies, led to axon degeneration without altering lamin B2 levels in the soma. These results indicate that lamin B2 functions in the

axon to promote axon survival independently from its role in the nucleus. By what mechanism, then, might lamin B2 play a role in axon survival? A first indication of its function in axons came from its localization: in axons, lamin B2 immunolabeling was found to coincide well with mitochondria. Furthermore, lamin B2 knockdown led to elongated mitochondrial morphology and reduced the mitochondrial potential necessary to drive ATP synthesis. This was also accompanied by reduced bidirectional movement of vesicles in the axon, a process heavily dependent on the ATP produced by mitochondria. These data show that lamin B2 promotes mitochondrial function, providing a plausible explanation for its effects on axon survival. Taken together, these results clearly show that lamin B2 is synthesized within the axon, and provide impressive evidence that this local synthesis is required for maintenance of RGC axons in vivo within the tectum. Regarding the precise developmental roles of this mechanism, these interesting results suggest more than one potential model.