Distinct cellular and molecular mechanisms mediate initial axon development and adult-stage axon regeneration in C. elegans

Department of Physics and Center for Brain Science, Harvard University, Cambridge, MA 02138, USA.
Development (Impact Factor: 6.46). 04/2008; 135(6):1129-36. DOI: 10.1242/dev.013995
Source: PubMed


The molecular and cellular mechanisms that allow adult-stage neurons to regenerate following damage are poorly understood. Recently, axons of motoneurons and mechanosensory neurons in adult C. elegans were found to regrow after being snipped by femtosecond laser ablation. Here, we explore the molecular determinants of adult-stage axon regeneration using the AVM mechanosensory neurons. The first step in AVM axon development is a pioneer axonal projection from the cell body to the ventral nerve cord. We show that regeneration of the AVM axon to the ventral nerve cord lacks the deterministic precision of initial axon development, requiring competition and pruning of unwanted axon branches. Nevertheless, axons of injured AVM neurons regrow to the ventral nerve cord with over 60% reliability in adult animals. In addition, in contrast to initial development, axon guidance during regeneration becomes heavily dependent on cytoplasmic protein MIG-10/Lamellipodin but independent of UNC-129/TGF-beta repellent and UNC-40/DCC receptor, and axon growth during regeneration becomes heavily dependent on UNC-34/Ena and CED-10/Rac actin regulators. Thus, C. elegans may be used as a genetic system to characterize novel cellular and molecular mechanisms underlying adult-stage nervous system regeneration.

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    • "Laser axotomies were performed using a femtosecond pulsed infrared laser (Coherent Inc.) and a 60X, 1.4 NA objective as described previously [12]. We acquired images using an automated computer controlled microscope system (Nikon) that allowed for time-lapse imaging of multiple (∼15) worms in parallel. "
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    ABSTRACT: One advantage of the nematode Caenorhabditis elegans as a model organism is its suitability for in vivo optical microscopy. Imaging C. elegans often requires animals to be immobilized to avoid movement-related artifacts. Immobilization has been performed by application of anesthetics or by introducing physical constraints using glue or specialized microfluidic devices. Here we present a method for immobilizing C. elegans using polystyrene nanoparticles and agarose pads. Our technique is technically simple, does not expose the worm to toxic substances, and allows recovery of animals. We evaluate the method and show that the polystyrene beads increase friction between the worm and agarose pad. We use our method to quantify calcium transients and long-term regrowth in single neurons following axotomy by a femtosecond laser.
    Full-text · Article · Jan 2013 · PLoS ONE
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    • "The mechanisms underlying axon regeneration have been studied in the case of one particular type of neuron, the so-called AVM mechanosensory neurons (Gabel et al. 2008). Two important differences were observed as compared to initial axon formation: The regeneration of the axon is much less precise that its initial formation, requiring competition and pruning of unwanted axon branches not found during development; axon guidance and growth also rely on different molecules during regeneration and development (Gabel et al. 2008). Taken together, the experimental data reviewed here show that, across phyla, regeneration mechanisms can be considered as strongly different from developmental mechanisms. "
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    ABSTRACT: Regeneration capabilities are found in most or all animals. Whether regeneration is part of the development of an animal or a distinct phenomenon independent of development is a debatable question. If we consider regeneration as a process belonging to development, similarly to embryogenesis or metamorphosis, the existence of regenerative capabilities in adults can be seen as an argument in favor of the theory that development continues throughout the life of animals. Here I perform a comparative analysis of regeneration versus “classical” developmental processes in animals in order to determine to what extent these processes are inclusive or distinct. I identify the existence of regeneration-specific processes, i.e., processes that occur during the regeneration, but not the initial development, of a given structure. In addition, I find that seemingly similar processes acting during development and regeneration may have differential molecular and cellular bases. I thus conclude that there are significant differences between regeneration processes in adult animals and developmental processes occurring during earlier phases of the life cycle. The existence of regenerative capabilities in adult animals can therefore not be used as an argument in favor of the idea that development spans the whole life. KeywordsCell differentiation–Dedifferentiation–Development–Epimorphosis–Molecular mechanisms–Regeneration–Stem cells
    Full-text · Article · Dec 2011 · Biological Theory
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    • "Also notable is the ability of fs laser insults to kill with single cell accuracy. The utility of fs lasers has been demonstrated in chicks, pigs, zebrafish, Drosophila, and C. elegans, [22], [23], [24], [25], [26], [27]. However, despite the importance of Xenopus as an experimental system with an important history of ablation experiments, laser ablation has not been tried on these embryos. "
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    ABSTRACT: With the goal of learning to induce regeneration in human beings as a treatment for tissue loss, research is being conducted into the molecular and physiological details of the regeneration process. The tail of Xenopus laevis tadpoles has recently emerged as an important model for these studies; we explored the role of the spinal cord during tadpole tail regeneration. Using ultrafast lasers to ablate cells, and Geometric Morphometrics to quantitatively analyze regenerate morphology, we explored the influence of different cell populations. For at least twenty-four hours after amputation (hpa), laser-induced damage to the dorsal midline affected the morphology of the regenerated tail; damage induced 48 hpa or later did not. Targeting different positions along the anterior-posterior (AP) axis caused different shape changes in the regenerate. Interestingly, damaging two positions affected regenerate morphology in a qualitatively different way than did damaging either position alone. Quantitative comparison of regenerate shapes provided strong evidence against a gradient and for the existence of position-specific morphogenetic information along the entire AP axis. We infer that there is a conduit of morphology-influencing information that requires a continuous dorsal midline, particularly an undamaged spinal cord. Contrary to expectation, this information is not in a gradient and it is not localized to the regeneration bud. We present a model of morphogenetic information flow from tissue undamaged by amputation and conclude that studies of information coming from far outside the amputation plane and regeneration bud will be critical for understanding regeneration and for translating fundamental understanding into biomedical approaches.
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