Differentiation of nuclei during keratinization in middle ear cholesteatoma. DNA cytophotometry completed by computerized image analysis.

Quantitative DNA cytophotometric techniques were applied to judge the alteration (differentiation) and ultimate fate of nuclei during keratinization in human middle ear cholesteatoma. Compared with a healthy epidermis, a tendency towards postponed nuclear degradation was noticed. Two patterns governing the loss of DNA are recognized. In one group, the mean nuclear DNA content declines continuously, starting in the nearest suprabasal layers and continuing throughout the prickle and granular cell stages, where the ultimate degeneration of nuclei takes place. This pathway corresponds to that observed in epidermis, but evolves more slowly. In another group of samples, the onset of the DNA decline is delayed to the upper prickle cells, exceptionally to more terminal stages of keratinization. During matrix keratinization, a profound nuclear remodelling takes place, similar to that in epidermal tissues, as far as eu- and heterchromatin DNA and area data are concerned. However, euchromatinization of nuclei in matrix prickle cells is more pronounced than in epidermal tissues. The topography of residual heterochromatic clumps does not reflect a persistent margination as in epidermal nuclei, but is the result of more individualized rearrangements. The changes in karyotype are less elaborate when the complete decline of the nuclear DNA content only occurs during terminal keratinization.