Differentiation-related Patterns of Expression of Proteins of Intermediate-size Filaments in Tissues and Cultured Cells

In cell biology, as in daily life, a common way of human thinking that is seductive, but not necessarily correct, leads to the conclusion that things that look alike are alike or even identical. This obvious dominance of expectation of homologies seems surprising in view of the numerous examples of analogies, i.e., formations of similar shapes and structures from different components and materials which biology has provided both in macroscopic and microscopic morphologies. Among the cytoskeletal filaments, striking homology of protein subunit components has been demonstrated in a diversity of cells as the predominant structural principle of formation in microfilaments and microtubules that are ubiquitous cell components throughout the eukaryotes. In contrast, it has been found with some surprise that a third category of cytoskeletal filaments is present, often in abundance, in cells of vertebrate animals. The intermediate-size filaments can be formed in different cell types by different proteins that...