Extinction of organelles in differentiating epidermis

In the dorsal skin of fetal rats, the epidermis on day 16 of gestation cons isted of a single or a few layers of undifferentiated cells, and it develop ed to display the full strata, i.e. the stratum ts.) corneum thorny layer), s. granulosum (granular layer), s, spinosum (spinous layer), and s. germin ativum (basal layer) by the day of birth. Perinuclear electron lucent speci al areas, which were also detectable by conventional staining under light m icroscope, appeared in the cells of the s. spinosum or the s. granulosum on the day of birth. We call such an area the "perinuclear compartment (PNC)" . The PNC was not partitioned by membranous structures either. Typical PNCs became recognizable on the day of birth. The cell nuclei seemed to be dige sted inside of the PNC of the cells located in the outermost area of the s. granulosum or sometimes in the boundary between the s. granulosum and the s, corneum.: In the initial phase of nuclear extinction, morphology of the nucleus undergoing degeneration resembles that of apoptotic cells. In compa rison to the morphological degeneration of the nucleus, DNA fragmentation w as suggested to occur earlier. Localization of cathepsin B and cathepsin D in the s. spinosum and s. granulosum as revealed by immunohistochemistry, t ogether with an electron microscopic study on the appearance of autophagoso mes in those areas, suggested a contribution of autophagy to the digestion of organelles including mitochondria and endoplasmic reticula in the termin al differentiation of epidermal cells.