Axon Regeneration Pathways Identified by Systematic Genetic Screening in C. elegans

Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA.
Neuron (Impact Factor: 15.05). 09/2011; 71(6):1043-57. DOI: 10.1016/j.neuron.2011.07.009
Source: PubMed

ABSTRACT The mechanisms underlying the ability of axons to regrow after injury remain poorly explored at the molecular genetic level. We used a laser injury model in Caenorhabditis elegans mechanosensory neurons to screen 654 conserved genes for regulators of axonal regrowth. We uncover several functional clusters of genes that promote or repress regrowth, including genes classically known to affect axon guidance, membrane excitability, neurotransmission, and synaptic vesicle endocytosis. The conserved Arf Guanine nucleotide Exchange Factor (GEF), EFA-6, acts as an intrinsic inhibitor of regrowth. By combining genetics and in vivo imaging, we show that EFA-6 inhibits regrowth via microtubule dynamics, independent of its Arf GEF activity. Among newly identified regrowth inhibitors, only loss of function in EFA-6 partially bypasses the requirement for DLK-1 kinase. Identification of these pathways significantly expands our understanding of the genetic basis of axonal injury responses and repair.

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Available from: Bruce Bowerman, May 08, 2014
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    • "Statistics: ANOVA; ***p < 0.01. studies of CAMSAPs (see below) and because an increase in dynamic MTs correlates with enhanced regrowth in mutants such as efa-6 (Chen et al., 2011). These observations suggest the absolute level of dynamic MTs may not be the critical determinant of regrowth capacity and that, instead, the change in the number of dynamic MTs after injury may be key. "
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    ABSTRACT: Precise regulation of microtubule (MT) dynamics is increasingly recognized as a critical determinant of axon regeneration. In contrast to developing neurons, mature axons exhibit noncentrosomal microtubule nucleation. The factors regulating noncentrosomal MT architecture in axon regeneration remain poorly understood. We report that PTRN-1, the C. elegans member of the Patronin/Nezha/calmodulin- and spectrin-associated protein (CAM-SAP) family of microtubule minus-end-binding proteins, is critical for efficient axon regeneration in vivo. ptrn-1-null mutants display generally normal developmental axon outgrowth but significantly impaired regenerative regrowth after laser axotomy. Unexpectedly, mature axons in ptrn-1 mutants display elevated numbers of dynamic axonal MTs before and after injury, suggesting that PTRN-1 inhibits MT dynamics. The CKK domain of PTRN-1 is necessary and sufficient for its functions in axon regeneration and MT dynamics and appears to stabilize MTs independent of minus-end localization. Whereas in developing neurons, PTRN-1 inhibits activity of the DLK-1 mitogen-activated protein kinase (MAPK) cascade, we find that, in regeneration, PTRN-1 and DLK-1 function together to promote axonal regrowth.
    Cell Reports 11/2014; 9(3):874-883. DOI:10.1016/j.celrep.2014.09.054 · 8.36 Impact Factor
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    • "We have shown that regeneration of individual GABAergic motor neurons requires the HSPG syndecan. Our findings are confirmed by recent regeneration screens in distinct neuron types (Chen et al., 2011; Nix et al., 2014), supporting the idea that syndecan is generally required during regeneration. Importantly , while most genes affecting regeneration in C. elegans modulate the frequency of growth cone formation or the length of extension, the growth cone collapse defects we describe are unique among regeneration phenotypes in C. elegans and argue that genetic pathways exist to promote aspects of axon regeneration that are not yet fully appreciated . "
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    ABSTRACT: Growth cones facilitate the repair of nervous system damage by providing the driving force for axon regeneration. Using single-neuron laser axotomy and in vivo time-lapse imaging, we show that syndecan, a heparan sulfate (HS) proteoglycan, is required for growth cone function during axon regeneration in C. elegans. In the absence of syndecan, regenerating growth cones form but are unstable and collapse, decreasing the effective growth rate and impeding regrowth to target cells. We provide evidence that syndecan has two distinct functions during axon regeneration: (1) a canonical function in axon guidance that requires expression outside the nervous system and depends on HS chains and (2) an intrinsic function in growth cone stabilization that is mediated by the syndecan core protein, independently of HS. Thus, syndecan is a regulator of a critical choke point in nervous system repair.
    Cell Reports 07/2014; 8(1). DOI:10.1016/j.celrep.2014.06.008 · 8.36 Impact Factor
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    • "This provides unparalleled control of the lesion and produces minimal scarring, which may be useful in distinguishing between neuron-intrinsic and -extrinsic mechanisms of axon regeneration. This laser ablation technique has also been used in the C. elegans model of axon regeneration [55] [56] . Such rapid improvements in in vivo imaging techniques will provide unprecedented temporo-spatial resolution of axon regeneration. "
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    ABSTRACT: With advances in genetic and imaging techniques, investigating axon regeneration after spinal cord injury in vivo is becoming more common in the literature. However, there are many issues to consider when using animal models of axon regeneration, including species, strains and injury models. No single particular model suits all types of experiments and each hypothesis being tested requires careful selection of the appropriate animal model. in this review, we describe several commonly-used animal models of axon regeneration in the spinal cord and discuss their advantages and disadvantages.
    Neuroscience Bulletin 08/2013; 29(4):436-44. DOI:10.1007/s12264-013-1365-4 · 2.51 Impact Factor
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