Quick-freeze, deep etch visualization of the cytoskeleton beneath surface differentiations of intestinal epithelial cells

Abstract

The cytoskeleton that supports microvilli in intestinal epithelial cells was visualized by the quick-freeze, deep-etch, rotary-replication technique (Heuser and Salpeter. 1979. J. Cell Biol. 82:150). Before quick freezing, cells were exposed to detergents or broken open physically to clear away the granular material in their cytoplasm that would otherwise obscure the view. After such extraction cells still displayed a characteristic organization of cytoskeletal filaments in their interior. Platinum replicas of these cytoskeletons had sufficient resolution to allow us to identify the filament types present, and to determine their characteristic patterns of interaction. The most important new finding was that the apical 'terminal web' in these cells, which supports the microvilli via their core bundles of actin filaments, does not itself contain very much actin but instead is comprised largely of narrow strands that interconnect adjacent actin bundles with one another and with the underlying base of intermediate filaments. These strands are slightly thinner than actin, do not display actin's 53 Å periodicity, and do not decorate with myosin subfragment S1.