Retinoic acid can change normal differentiation of rat egg-cylinders cultured in vitro.

The modified organ culture of rat egg cylinders provides favorable conditions for 2 weeks for the differentiation of main tissue types. To study the effect of retinoids on early rodent differentiation, retinoic acid (RA) was added in various concentrations to serum-supplemented or serum-free medium. Explant survival decreased when RA was added to serum-free medium. Although the cartilage was well differentiated even in cultures deprived of serum, RA inhibited chondrogenesis in all cultures without or with serum. The frequency of columnar epithelium was higher and its folds more often present when RA was added to the medium. Keratinization of squamous epithelium depended on the RA concentration added to the medium, and was almost absent when the concentration was high. Other tissues often present in serum-supplemented medium (such as neuroblasts and myotubes) were not affected by RA, a result that differs from those obtained in other experimental systems.

Differentiation and growth of rat egg-cylinders cultured in vitro in a serum-free and protein-free medium.

Modified organ cultures of rat egg-cylinders were grown for 2 weeks in Eagle's minimal essential medium (MEM) without serum. Differentiation of epidermis and cartilage in the cultures deprived of serum was comparable to that in fully serum-supplemented medium, whereas other differentiated tissues were rare or absent. The purpose of the experiment was to determine whether terminal tissue differentiation is modified by various added factors. The factors used affected the growth and/or differentiation of explants as follows: bovine serum albumin and human transferrin had a positive permissive influence on the appearance of neuroblasts; human transferrin alone stimulated the formation of lentoids, a relatively rare tissue. Retinoic acid inhibited cartilage formation and stimulated the differentiation of cylindrical epithelium; neural growth factor inhibited the growth of explants; and 5-azacytidine impeded the survival of explants. One can conclude that these factors influenced the growth and differentiation of the early rat embryos cultured in a chemically defined medium.

Effect of various sera on cultured rodent embryonic shields.

The modified organ culture of rodent embryonic shields, developed in our laboratory, has been shown to provide favorable conditions for the differentiation of the main tissues in teratoma-like explants. The purpose of the experiment was to discover whether tissue differentiation is modified by different sorts of sera used in the liquid medium. Rat explants showed an increase of the incidence of cartilage when cultured in at least 20% homologous serum in comparison with human and fetal bovine sera. Mouse explants did not grow in mouse serum, whereas rat serum stimulated the development of endoderm-like epithelium, and fetal bovine serum brought about more neural tissue.