Abstract
In neuronal processes, microtubules (MTs) provide structural support and serve as tracks for molecular motors. While it is known that neuronal MTs are more stable than MTs in non-neuronal cells, the molecular mechanisms underlying this stability are not fully understood. In this study, we used live fluorescence microscopy to show that the C. elegans CAMSAP protein PTRN-1 localizes to puncta along neuronal processes, stabilizes MT foci, and promotes MT polymerization in neurites. Electron microscopy revealed that ptrn-1 null mutants have fewer MTs and abnormal MT organization in the PLM neuron. Animals grown with a MT depolymerizing drug caused synthetic defects in neurite branching in the absence of ptrn-1 function, indicating that PTRN-1 promotes MT stability. Further, ptrn-1 null mutants exhibited aberrant neurite morphology and synaptic vesicle localization that is partially dependent on dlk-1. Our results suggest that PTRN-1 represents an important mechanism for promoting MT stability in neurons. DOI: http://dx.doi.org/10.7554/eLife.01498.001.
Highlights
In neurons, microtubules (MTs) provide structural support, provide tracks that molecular motors use to transport cargo from the cell body to the synapses, and promote the establishment and maintenance of neuronal polarity
As the other PTRN-1 isoform, PTRN-1b, lacks the CKK domain, which is the domain required for MT binding in other CAMSAP proteins, we focused on the PTRN-1a isoform (Meng et al, 2008; Baines et al, 2009; Goodwin and Vale, 2010)
We focused on the PVD neuron, which elaborates a branching dendrite arbor from two primary dendrites that run laterally along the animal, as well as a single axon that extends ventrally to make presynaptic connections in the ventral nerve cord (VNC), thereby providing a useful system for visualizing multiple distinct processes (Figure 1A)
Summary
Microtubules (MTs) provide structural support, provide tracks that molecular motors use to transport cargo from the cell body to the synapses, and promote the establishment and maintenance of neuronal polarity. Many proteins bind along the side or at the plus end of neuronal MTs to promote MT stability (Conde and Cáceres, 2009). Tubulin posttranslational modifications contribute to the structure and function of neuronal MTs (Janke and Kneussel, 2010). Tubulin dimers can be added and removed from the plus end of an MT, the minus end depolymerizes continuously if not stabilized (Mimori-Kiyosue, 2011). Minus ends are anchored at the centrosome by the γ-tubulin ring complex (γ-TuRC). Ninein, another minus end-binding protein, both stabilizes MTs that have been released from the centrosome and anchors MTs at centrosomal and non-centrosomal sites (Mogensen et al, 2000)
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