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Ultrastructural properties of ciliary zonule microfibrils.
Elaine C Davis1, Robyn A Roth, John E Heuser
1Department of Cell Biology, The University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX, USA. elaine.davis@mcgill.ca
Journal of Structural Biology
|October 31, 2002
Summary
Quick-freeze deep-etch microscopy reveals microfibril ultrastructure as packed beads. This technique clarifies bead associations and suggests sonication may expose underlying filamentous structures.
Area of Science:
- Cell Biology
- Biophysics
- Microscopy
Background:
- Conflicting interpretations of microfibril ultrastructure exist with conventional electron microscopy.
- Previous methods involved fixation, dehydration, and heavy metal staining, potentially altering native structure.
Purpose of the Study:
- To clarify microfibril ultrastructure using a novel microscopy technique.
- To investigate the native 3D surface structure of microfibrils without artifact-inducing preparation steps.
Main Methods:
- Quick-freeze deep-etch (QFDE) microscopy was employed to visualize microfibrils.
- QFDE avoids fixation, dehydration, and heavy metal staining, preserving native structure.
Main Results:
- Microfibrils appear as tightly packed rows of bead-like subunits without interbead links.
- Larger beads at 50-nm intervals align laterally in bundles, suggesting organized associations.
- Sonicated microfibrils show a "beads on a string" appearance, with monomers exhibiting thread-like filaments.
Conclusions:
- QFDE microscopy provides a clearer view of microfibril organization.
- The "beads on a string" appearance may result from protein loss exposing filamentous substructures.
- This phenomenon could explain similar observations in other electron microscopy techniques.