Prevalent presence of periodic actin–spectrin-based membrane skeleton in a broad range of neuronal cell types and animal species

Abstract

Actin, spectrin, and associated molecules form a periodic, submembrane 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 appears periodic only in a small fraction of dendrites, typically in the form of isolated patches in subregions 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 disrupted in most presynaptic boutons but is present in an appreciable 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.ctin is critically involved in the regulation of neuronal polarization, differentiation, and growth of neuronal processes, cargo trafficking, and plasticity of synapses (1-3). Spectrin is an actin-binding protein that is important for the development and stabilization of axons and maintenance of neuronal polarization (4-6). In Caenorhabditis elegans, spectrin is important for the stability and integrity of axons under mechanical stress (4, 6) and for mechanosensation (6), and spectrin depletion results in axon breakage during animal locomotion (4). In Drosophila, spectrin has been shown to be involved in axonal path finding (7) and stabilization of presynaptic terminals (8). In mice, spectrin null mutations are embryonically lethal, and neurons with spectrin knockdown display defects in axonal initial segment assembly (5, 9, 10).Actin and spectrin form a 2D polygonal lattice structure underneath the membrane of erythrocytes (11). Recently, a novel form of actin-spectrin-based submembrane skeleton structure was discovered in neuronal axons (12) using superresolution STORM imaging (13,14). This membrane-associated periodic skeleton (MPS) has been observed in both fixed and live cultured neurons (12, 15, 16) and in brain tissue sections (12). In this structure, short actin filaments are organized into repetitive, ring-like structures that wrap around the circumference o...

Revealing compartmentalised membrane diffusion in living cells with interferometric scattering microscopy

“…3a,b), similar to our previous observation of membrane compartments in the axon initial segment with QD-labelled membrane proteins. 19 Numerous reports highlight the existence of a periodic cortical actinspectrin network in axons 15,[20][21][22] and possibly dendrites 23,24 , and we found the periodic arrangement of membrane compartments to be alternating with such actin rings in our fluorescence imaging studies. 19 We thus asked whether we could find evidence for the same 180 -200 nm periodicity in our iSCAT trajectory data.…”

Actin regulation by tropomodulin and tropomyosin in neuronal morphogenesis and function

“…The actin-spectrin network has a unique periodic structure along the axon (He et al, 2016; Xu et al, 2013). Tmods are known to be important players in regulating the length of actin filaments in the actin-spectrin network of red blood cells (Moyer et al, 2010b).…”

The Spectrin-Actin-Based Periodic Cytoskeleton as a Conserved Nanoscale Scaffold and Ruler of the Neural Stem Cell Lineage

“…Although initially noted in neuronal axons as adducin-capped actin rings connected by spectrin tetramers to form a periodic, one-dimensional (1D) lattice of well-defined, ~180- to 190-nm periodicity (Xu et al, 2013), related periodic or quasi-periodic cytoskeletal structures have also been observed in dendrites (D’Este et al, 2015; Han et al, 2017) and certain glial cell types (D’Este et al, 2016, 2017; He et al, 2016). Such periodic nanostructures are markedly different from the traditional view of the actin-based cytoskeleton in common mammalian cell types (e.g., dense filament networks and bundles in fibroblasts and epithelial cells) (Chhabra and Higgs, 2007; Pollard and Cooper, 2009; Xu et al, 2012) as well as the spectrin-actin-based cytoskeleton in erythrocytes (2D triangular lattices of short actin filaments connected by spectrin tetramers) (Baines, 2010; Bennett and Baines, 2001; Bennett and Gilligan, 1993; Fowler, 2013; Pan et al, 2018).…”