Apoptosis of the intestinal principal cells of Xenopus larvae exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin

In our previous work using paraffin-embedded sections, we determined that Xenopus larvae exposed to 200 ppb 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) for 5 days from shortly after fertilization to the early larval stage showed a shortening of the digestive tract and a loss of mucosal epithelium cells due to exfoliation into the gut cavity. In the current study, we ultrastructurally examined the mucosal epithelium of the gut of TCDD-exposed Xenopus larvae 12 days after fertilization. Exfoliated cell structures at the villus tip and in the lumen were equipped with a microvillus portion and occasionally had terminal web-like structures seen by ultramicroscopy. As these exfoliated structures had nuclear fragments with condensed chromatin, they were considered to be apoptotic bodies derived from the principal cells of the epithelium. In addition, many membrane-bound cell fragments-identified as apoptotic bodies derived from the principal cells based on their ultrastructural features-were observed at the basal side of the mucosal epithelium. These apoptotic bodies were phagocytized and digested chiefly by the neighboring intact principal cells. No such cells and/or cell fragments showing apoptotic features were observed in the controls. Our observations indicate that marked apoptosis occurs in the intestinal principal cells of TCDD-exposed larvae, which may result in the shortening of the gut.