Stimulation of epidermal growth by the egg white and yolk

It was found that white and yolk of the egg stimulated DNA synthesis of chick embryo epidermal culture. The epidermis cultured with yolk grew well in a manner similar to that with chick embryo extract, but the culture with egg white was poorer in growth than that with yolk. The mitogenic activity of egg white was inactivated by a heat treatment at 70 degrees C, while yolk was more heat-resistant. A heat-stable yolk fraction (hY fraction) which stimulated DNA synthesis of chick embryo epidermis was isolated by heat treatment at 98 degrees C. The mitogenic activity was enhanced by the addition of both egg white and hY fraction in the culture medium. The enhancement of epidermal growth by such an addition was confirmed by histological observations of the cultured epidermis. In embryonic skin, the growth and differentiation of epidermis is influenced by the nature of mesenchyme is proximity to the epidermal cells. The epidermis isolated from dermis does not grow or differentiate when cultivated in a chemically defined medium, although the tissue in whole skin does grow in the same medium. However, the isolated epidermis proliferates on non-living substrate such as membrane filter or collagen gel when cultured in a medium which contains chick embryo extract. This epidermal growth promoting property of chick embryo extract is inactivated by heat treatment or trypsin digestion.(ABSTRACT TRUNCATED AT 250 WORDS)