Floriana Bulic-Jakuš, Maja Vlahovic, Gordana Juric-Lekic, Vesna Crnek-Kunstelj and Draško Šerman

Developmental processes in gastrulating rat embryos were investigated by using an original, serum-free, chemically defined model system. 9.5-day-old rat embryos, without extraembryonic membranes, were cultivated at the air–liquid interface in a serum-free medium, with and without a protein supplement, for 2 weeks. A teratogenic, demethylating agent, 5-azacytidine, was added to serum-free and protein-free culture medium and to serum-free medium supplemented with human transferrin. A single dose of 5-azacytidine impaired the survival, growth and differentiation of embryos in protein-free medium and serum-free medium with transferrin. In contrast, repeated exposure to 5-azacytidine was required to impair growth in serum-supplemented medium. It was concluded that the activity of 5-azacytidine was easier to detect in a simple, chemically defined medium than in a serum-supplemented medium. This serum-free in vitro method could be useful in screening for teratogenic or embryotoxic substances during gastrulation, the most critical stage of mammalian development.
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