Inductive action of epithelium on differentiation of intestinal connective tissue of Xenopus laevis tadpoles during metamorphosis in vitro.

The action of the epithelium on differentiation of connective tissue cells of Xenopus small intestine during metamorphosis was investigated by using culture and morphological techniques. Connective tissue fragments isolated from the small intestine at stage 57 were cultivated in the presence or absence of homologous epithelium. In the presence of the epithelium, metamorphic changes in the connective tissue were fully induced by hormones including thyroid hormone (T3), as during spontaneous metamorphosis, whereas they were partially induced in the absence of the epithelium. Macrophage-like cells showing non-specific esterase activity in the connective tissue were much fewer in the absence of the epithelium than in the presence of it, and aggregates of fibroblasts possessing well-developed rough endoplasmic reticulum developed only in the presence of the epithelium. Just before the aggregation of the fibroblasts, the connective tissue close to the epithelium became intensely stained with concanavalin A (ConA) and wheat germ agglutinin (WGA). The present results indicate that the epithelium plays important roles in the differentiation of intestinal connective tissue cells, which in turn affect the epithelial transformation from larval to adult form during anuran metamorphosis. Thus, the tissue interaction between the epithelium and the connective tissue in the anuran small intestine is truly bidirectional.