Abstract
In the dorsal skin of fetal rats, the epidermis on day 16 of gestation consisted of a single or a few layers of undifferentiated cells, and it developed to display the full strata, i. e the stratum (s.) corneum (horny layer), s. granulosum (granular layer), s. spinosum (spinous layer), and s. germinativum (basal layer) by the day of birth. Perinuclear electron lucent special areas, which were also detectable by conventional staining under light microscope, appeared in the cells of the s. spinosum or the s. granulosum on the day of birth. We call such an area the “peri-nuclear 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 digested 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 comparison to the morphological degeneration of the nucleus, DNA fragmentation was suggested to occur earlier. Localization of cathepsin B and cathepsin D in the s. spinosum and s. granulosum as revealed by immunohistochemistry, together with an electron microscopic study on the appearance of autophagosomes in those areas, suggested a contribution of autophagy to the digestion of organelles including mitochondria and endoplasmic reticula in the terminal differ-entiation of epidermal cells.
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