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Differences in protein mobility between pioneer versus follower growth cones.

ABSTRACT: Navigating growth cones need to integrate, process and respond to guidance signals, requiring dynamic information transfer within and between different compartments. Studies have shown that, faced with different navigation challenges, growth cones display dynamic changes in growth kinetics and morphologies. However, it remains unknown whether these are paralleled by differences in their internal molecular dynamics. To examine whether there are protein mobility differences during guidance, we developed multiphoton fluorescence recovery after photobleaching methods to determine molecular diffusion rates in pathfinding growth cones in vivo. Actively navigating growth cones (leaders) have consistently longer recovery times than growth cones that are fasciculated and less actively navigating (followers). Pharmacological perturbations of the cytoskeleton point to actin as the primary modulator of diffusion in differently behaving growth cones. This approach provides a powerful means to quantify mobility of specific proteins in neurons in vivo and reveals that diffusion is important during axon navigation.

SUBMITTER: Kulkarni RP

PROVIDER: S-EPMC1783102 | biostudies-literature | 2007 Jan

REPOSITORIES: biostudies-literature

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Differences in protein mobility between pioneer versus follower growth cones.

Kulkarni Rajan P RP Bak-Maier Magdalena M Fraser Scott E SE

Proceedings of the National Academy of Sciences of the United States of America 20070117 4

Navigating growth cones need to integrate, process and respond to guidance signals, requiring dynamic information transfer within and between different compartments. Studies have shown that, faced with different navigation challenges, growth cones display dynamic changes in growth kinetics and morphologies. However, it remains unknown whether these are paralleled by differences in their internal molecular dynamics. To examine whether there are protein mobility differences during guidance, we dev ...[more]

PMID: 17229842

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Project description:To form operative neuronal networks neurons connect to their synaptic partners by axonal outgrowth guided by the movement of the axon tip, a specialized structure known as the growth cone (GC), which travels along stereotypical paths by sensing extracellular guidance cues. Interestingly, GCs contain complex transcriptomes and different guidance cues can rapidly regulate the translation of specific mRNAs which help to remodel the GC cytoskeleton thus steering axon navigation. However, the full landscape of proteomic changes elicited by different cues is not known and the precise protein synthesis (PS)-dependent molecular mechanisms underlying GC repulsive and attractive turning remain largely elusive. Here we have investigated the cue-induced changes in the nascent proteome by pulse Stable Isotope Labeling by Amino acids in Cell culture (pSILAC) in somaless developing retinal axons derived from Xenopus laevis primary cultures. The experimental approach presented major challenges due to the limited quantity of axonal material (~2 μg per condition) and to the desired rapid (5-15 min) time-scale (no previous work has accomplished SILAC with a pulse less than 20 min). To overcome these difficulties we used a superior protocol, termed Single-Pot Solid- Phase-enhanced Sample Preparation, based on ultrasensitive paramagnetic bead technology which allows high proteomic sample recovery from sub-microgram amounts of material. By employing this method we were able to identify up to 500 newly synthesized proteins after only 5 min of pSILAC. Subsequently, we successfully validated the purity and viability of the axonal samples and the reliability of the method. Finally, to characterize and quantify the global patterns of the axonal translational changes in response to specific guidance cues and to unravel the switch between repulsive and attractive responses, we carried out pSILAC in the presence of different repulsive cues and pharmacological reagents that convert repulsion into attraction. Our results uncovered a surprisingly high level of translational activity within the axonal compartment, even in basal conditions. Remarkably, comparative analysis revealed many changes in the nascent proteome in response to different cues, some distinct and some common. Interestingly, several proteins showed cue-specific downregulation. Taken together, our findings suggest a comprehensive GC PS-dependent chemotropic model and novel cue-specific molecular mechanisms possibly underlying the integration of chemotropic responses.

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Differences in protein mobility between pioneer versus follower growth cones.

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Differences in protein mobility between pioneer versus follower growth cones.

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