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bioRxiv2016

MTQuant: "Seeing" Beyond the Diffraction Limit in Fluorescence Images to Quantify Neuronal Microtubule Organization

MotivationMicrotubules (MTs) are polarized polymers that are critical for cell structure and axonal transport. They form a bundle in neurons, but beyond that, their organization is relatively unstudied.\n\nResultsWe present MTQuant, a method for quantifying MT organization using light microscopy, which distills three parameters from MT images: the spacing of MT minus-ends, their average length, and the average number of MTs in a cross-section of the bundle. This method allows for robust and rapid in vivo analysis of MTs, rendering it more practical and more widely applicable than commonly-used electron microscopy reconstructions. MTQuant was successfully validated with three ground truth data sets and applied to over 3000 images of MTs in a C. elegans motor neuron.\n\nAvailabilityMATLAB code is available at http://roscoope.github.io/MTQuant\n\nContacthorowitz@stanford.edu\n\nSupplementary informationSupplementary data are available at Bioinformatics online.

Bioinformatics↗

bioRxiv2016

Prevalent Presence of Periodic Actin-spectrin-based Membrane Skeleton in a Broad Range of Neuronal Cell Types and Animal Species

Actin, spectrin and associated molecules form a periodic, sub-membrane cytoskeleton in the axons of neurons. For a better understanding of this membrane-associated periodic skeleton (MPS), it is important to address how prevalent this structure is in different neuronal types, different subcellular compartments, and across different animal species. Here, we investigated the organization of spectrin in a variety of neuronal and glial-cell types. We observed the presence of MPS in all of the tested neuronal types cultured from mouse central and peripheral nervous systems, including excitatory and inhibitory neurons from several brain regions, as well as sensory and motor neurons. Quantitative analyses show that MPS is preferentially formed in axons in all neuronal types tested here: spectrin shows a long-range, periodic distribution throughout all axons, but only appears periodic in a small fraction of dendrites, typically in the form of isolated patches in sub-regions of these dendrites. As in dendrites, we also observed patches of periodic spectrin structures in a small fraction of glial-cell processes in four types of glial cells cultured from rodent tissues. Interestingly, despite its strong presence in the axonal shaft, MPS is absent in most presynaptic boutons, but is present in a substantial fraction of dendritic spine necks, including some projecting from dendrites where such a periodic structure is not observed in the shaft. Finally, we found that spectrin is capable of adopting a similar periodic organization in neurons of a variety of animal species, including Caenorhabditis elegans, Drosophila, Gallus gallus, Mus musculus and Homo sapiens.

Neuroscience↗