Changes in morphology and cell proliferation during vitamin A‐lnduced mucous metaplasia of developing chick scale cultured in vitro

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Abstract
Throughout the process of vitamin A (V‐A)‐induced mucous metaplasia of the scale epidermis of a 12‐day chick embryo, changes in the activities of cell proliferation were investigated in reference to morphological changes. In both the control and V‐A cultures after 5 days, a dynamic steady state was established among the stratified layers which differentiated into keratinizing epidermis during the first 7 days.In the control, cell proliferates within only the basal layer and the cell cycle time, except Tg2, increased during 30 days of culture. In the V‐A culture, this tendency was reversed in each parameter between day 10 and day 13, when symptoms of mucous metaplasia became morphologically prominent. On day 13 in the V‐A culture, superficial cornified cell layers were sloughed off as whole sheets and concurrently DNA synthesis was reactivated throughout the entire cell layers of the epithelium.The correlation between two of five cell cycle times (Tgc, Tg1, Ts, Tg2, Tm) was statistically treated as linear regression lines and gave highly significant coefficients in every case. The regression coefficients between Ts and Tgc and Ts and Tgl in V‐A culture are significantly (P < 0.01) smaller than those in the control. It was found that V‐A induced sequential alterations in mucous metaplasia with respect both to morphology and proliferation activity in the epidermis of the chick embryo.