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Cytoskeleton (Hoboken). 2017 Nov;74(11):426-442. doi: 10.1002/cm.21410. Epub 2017 Sep 30.

High-resolution imaging of muscle attachment structures in Caenorhabditis elegans.

Author information

1
Department of Pathology, Emory University, Atlanta, Georgia 30322.
2
Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York 10461.
3
Department of Cell Biology, Emory University, Atlanta, Georgia 30322.

Abstract

We used structured illumination microscopy (SIM) to obtain super-resolution images of muscle attachment structures in Caenorhabditis elegans striated muscle. SIM imaging of M-line components revealed two patterns: PAT-3 (β-integrin) and proteins that interact in a complex with the cytoplasmic tail of β-integrin and localize to the basal muscle cell membrane [UNC-112 (kindlin), PAT-4 (ILK), UNC-97 (PINCH), PAT-6 (α-parvin), and UNC-95], are found in discrete, angled segments with gaps. In contrast, proteins localized throughout the depth of the M-line (UNC-89 (obscurin) and UNC-98) are imaged as continuous lines. Systematic immunostaining of muscle cell boundaries revealed that dense body components close to the basal muscle cell membrane also localize at cell boundaries. SIM imaging of muscle cell boundaries reveal "zipper-like" structures. Electron micrographs reveal electron dense material similar in appearance to dense bodies located adjacent to the basolateral cell membranes of adjacent muscle cells separated by ECM. Moreover, by EM, there are a variety of features of the muscle cell boundaries that help explain the zipper-like pattern of muscle protein localization observed by SIM. Short dense bodies in atn-1 mutants that are null for α-actinin and lack the deeper extensions of dense bodies, showed "zipper-like" structures by SIM similar to cell boundary structures, further indicating that the surface-proximal components of dense bodies form the "zipper-like" structures at cell boundaries. Moreover, mutants in thin and thick filament components do not have "dot-like" dense bodies, suggesting that myofilament tension is required for assembly or maintenance of proper dense body shape.

KEYWORDS:

C. elegans; electron microscopy; integrin adhesion sites; muscle; super resolution microscopy

PMID:
28921913
PMCID:
PMC5811768
DOI:
10.1002/cm.21410
[Indexed for MEDLINE]
Free PMC Article

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