Nuclear morphology of transitional keratinocytes in normal human epidermis.

Transitional keratinocytes (TK) of normal interfollicular human epidermis were studied by electron microscopy to provide more information on the ultrastructural nuclear and nucleolar changes during physiological keratinization. The results revealed that TK contained condensed nuclei in the initial stage, degraded nuclei in the advanced stage, and nuclear remnants in the late stage of their transformation into cornified cells. The condensed nuclei were essentially characterized by ultrastructural changes generally considered to reflect the cessation of RNA synthesis. The focal increase of density and the structural disintegration observed in the degraded nuclei of TK are apparently characteristic morphological features of degradation of nucleoproteins in these cells. Nuclear remnants contained altered nuclear envelope or similar structures and clumps of dense fibrillar material. Similar clumps of dense fibrils were present in the cytoplasm of both the TK with compact nuclear remnants and the TK with structural disintegration. This finding suggests that some dense fibrillar material of structurally disintegrating nuclei of TK is transported into the cytoplasm of these cells.