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Neurons have an elaborate architecture with specialized compartments like dendrites, cell bodies, axons, and synapses. The neuronal cytoskeleton is constituted of the microtubules, microfilaments, and neurofilaments and their distinct organization supports the neuronal compartments structurally and functionally1,2,3,4,5,6,7,8,9,10. Over the years, microtubule organization has been identified as a key determinant of neuronal polarity and function. As neurons undergo structural remodeling during development or regeneration, the microtubule dynamics and orientation determine the identity, polarized transport, growth, and development of various neuronal compartments7. It is, therefore, imperative to assess the microtubule dynamics and orientation in vivo to correlate with the neuronal remodeling process.
Microtubules are composed of protofilaments of α and β Tubulin heterodimers with dynamic plus ends and relatively stable minus ends11,12. The discovery of the plus tip complex and associated end binding proteins have enabled a platform to assess the microtubule organization13. End binding proteins (EBP) transiently associate with the growing plus ends of the microtubule and their association dynamics are correlated to the growth of the microtubule protofilaments14,15. Due to frequent association and dissociation of plus tip complex with the microtubule, the point spread function of GFP-tagged EBP appears as a "comet" in a timelapse movie15,16. Since the pioneering observation in mammalian neurons16, end binding proteins tagged with fluorescent proteins have been used to determine microtubule dynamics across different model systems and neuron types17,18,19,20,21,22,23.
Due to its simple nervous system and transparent body, C. elegans has proven to be an excellent model system to study neuronal remodeling during development and regeneration in vivo. Here we describe methods to label, image, and analyze the microtubule dynamics and growth during the development and regeneration of touch neurons in C. elegans. Using genetically encoded EBP-2::GFP, we imaged the microtubules in the PLM neuron, which allowed us to determine the polarity of the microtubules in two different neurites of this neuron24. This method allows observation and quantification of the EBP comets as a measure of microtubule dynamics in different cellular contexts, for example, the local changes in microtubule behavior that initiates axon regeneration following axotomy can be assessed using our protocol. This assay can be adapted to investigate the regulation of microtubule dynamics in various cellular processes in diverse cell types and genetic backgrounds.