Distribution of histidine-rich basic protein, a possible keratin matrix protein, in rat oral epithelium

The indirect fluorescent-antibody technique was used to locate histidine-rich basic protein, filaggrin. In the newborn, immunofluorescence was seen in the cornified layers and in keratohyalin granules throughout the mouth using antibody specific for epidermal filaggrin, a distribution similar to that in epidermis where it is thought that filaggrin functions as the keratin matrix protein. In the adult immunofluorescence was in keratohyalin granules of palate, buccal and tongue epithelium but in the stratum corneum was limited to the soft palate with weak, patchy areas in the densely keratinized epithelium of the hard palate and tongue. Immunofluorescence was delineated at the boundary between the soft and hard palates. A protein apparently identical to epidermal filaggrin was identified in extracts of newborn palate by its mobility on sodium dodecyl sulphate-polyacrylamide gels and subsequent reaction with the antibody used for immunofluorescent studies. This protein was not detected in extracts of adult oral epithelia. Both newborn and adult tissues contained high mol. wt cross-reactive protein, suggestive of the filaggrin-precursor protein extractable from keratohyalin granules. The distribution of filaggrin was consistent with its function as a keratin matrix protein in the newborn oral epithelium and some less densely keratinized regions of the adult. However, in the adult mouth, filaggrin is not detectable in the stratum corneum of the most densely keratinized regions. Thus, the protein must be lost or its antigenic sites altered with maturation of the animal, depending on the type and extent of keratinization.