A Pictorial History of the Neuronal Cytoskeleton

authors

• Leterrier Christophe

abstract

Neurons are the "delicate and elegant...butterflies of the soul," as Santiago Ramón y Cajal famously put it in his memoir (Zwirn, 2015). Neurons interconnect throughout the brain and body via the elaborate arborization of their dendrites and axon. Their cytoskeleton, the intricate array of microtubules, intermediate filaments, and actin filaments running throughout each neuron, allows them to build, maintain, and transform their fantastic architectures (Leterrier et al., 2017; Tas and Kapitein, 2018). The 40th anniversary of the Journal of Neuroscience first issue marks a great occasion to showcase how images have shaped our understanding of the neuronal cytoskeleton, from the early drawing of pioneers to the latest developments of microscope technology. I will follow how preparation and culture procedures, staining methods, and microscopy techniques each brought new insight on key neuronal structures, such as microtubules, the axonal growth cone, and dendritic spines. This history of the cytoskeleton in pictures begins in the 19th century with the drawings of gifted scientists/artists. Staining techniques, such as the Golgi method and its refinements, revealed not only the morphology of isolated neurons, but also the details of intraneuronal fibers, which were termed "neurofibrils." Beautiful drawings from light microscopy observations by Cajal and others depict these straight or wavy neurofibrils inside the cell body, dendrites, and axon of a variety of neurons (Fig. 1A,B, from Frixione, 2009). The advent of microphotography allowed images to be captured directly from the microscope, but drawings were still used throughout the 20th century to summarize findings as platonic ideals from numerous observations. Classic electron microscopy (EM) works from the 1950s to 1970s thus feature often beautiful, detailed drawings, such as the depiction of intermediate filament ("neurofilament") loops within presynapses from George Gray and Ray Guillery (Fig. 1C, from Gray and Guillery, 1966) or the summary of Victoria Chan-Palay's observations on the submembrane organization of the axon initial segment (Fig. 1D, from Chan-Palay, 1972).

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