Degeneration of Ribosomes in Keratinizing Cells: Possible Participation of RNase A in the Skin and Hair of Rat

抄録

The degeneration of organelles in the course of keratinization and in other terminal differentiation pathways has been studied mainly by electron microscopy. Here I show a panoramic view of the degeneration of ribosomes in sections of the skin epidermis, hair shaft and hair inner root sheath of neonatal rats by in situ hybridization using a complementary DNA probe for 28S-rRNA. As the keratinization advances, staining for 28S-rRNA decreases reciprocally. In contrast, immunohistochemical signals of RNase A increase in the spinous layers of the epidermis as well as in the corresponding differentiation stage of the inner root sheath of the hair, suggesting the contribution of this enzyme to the degeneration of ribosomes in these areas. In the hair shaft, however, RNase A was hardly detectable in any differentiation stage. RNase A is extraordinarily rich in the outer root sheath, which does not undergo keratinization, while 28S-rRNA was detected faintly in this tissue. Since the outer root sheath is thought to be a barrier to pathogens, RNase A may function as a weapon against retroviruses. In contrast to the outer root sheath, 28S-rRNA is rich in the basal layer of the epidermis and hair matrix of the hair bulb, while RNase A is poor in these tissues, which are located in the deep skin and undergo active cellular proliferation. Most dermal fibroblasts exhibit strong RNase A signal but weak 28S-rRNA signals. As exceptions, the dermal papilla and dermal sheath showed lower levels of RNase A.