It is impossible to understand keratinization disorders without knowing what is going on at molecular levels. We and others have been analyzing the issues of keratinization by means of (immuno)electron microscopy and found that this is quite a useful tool for molecular pathology. We summarize the recent advances in the biology and pathology of keratinization at ultrastructural and molecular levels. Tonofilaments, a morphological hallmark of keratinocytes, are composed of
keratins.
Epidermolytic hyperkeratosis, a
genetic disease of
keratin K1/K10, shows clumped tonofilaments that are shown to be actually composed of K1/K10 by immunoelectron microscopy. Distribution of
profilaggrin and its derivatives has also been revealed by immunoelectron microscopy. Defective interaction between
keratin and
filaggrin is seen in
epidermolytic hyperkeratosis. Transient nuclear localization of N-terminal domains of
profilaggrin is observed in the transitional cells of normal epidermis. Unique distribution of
trichohyalin was detected in
psoriasis. Distribution of various components of cornified cell envelopes including
involucrin and
loricrin in normal and abnormal keratinization can also be detected with this technique. Premature formation of
involucrin-rich cell envelopes are observed in
psoriasis vulgaris. Defects in cross-linking of
loricrin are detected in
transglutaminase 1 knockout mice, the animal model of
lamellar ichthyosis. Abnormal distribution of
loricrin has been detected in
genetic diseases of
loricrin (
loricrin keratoderma). By combining immunoelectron microscopy and
terminal deoxynucleotidyl transferase-mediated dUDP nick-end labeling (TUNEL) methods, the nature of TUNEL positive cells has also been unravelled.