Factors influencing fusion of rat palates grown in vitro

A technique is described for growth in vitro of embryonic rat palatal tissue on defined and semi‐defined media. Palatal fusion closely resembling that occurring in vivo is found in these preparations. Fusion occurs in a large number of cases even in the absence of an animal extract. However, development is improved if fetal calf serum is added to the synthetic medium. Using Leibovitz Medium L‐15 with 20% fetal calf serum, complete fusion was obtained in 87% of the palates, partial fusion in 9% and no fusion was found in only 4% of the palates cultured. Incorporation of galactoflavin, a riboflavin antagonist in a riboflavin‐deficient diet of the mother or in the culture medium results in a decreased number of complete fusions and corresponding increase in partial fusions. A suggestion is made as to the manner in which galactoflavin acts in vivo to produce palatal cleft, based on the incidence and type of clefts and the histological appearance of the palatal tissues. A method is described in which the tissue sections are sliced prior to culture so that the behavior of individual palatal shelves can be studied during the fusion process. Fusion occurs between shelves if the medial margins are apposed, regardless of whether the two shelves come from the same embryo, from littermate embryos, or from non‐littermate embryos. Some possibilities for application of this technique are suggested.