ANTEROPOSTERIOR GRADIENT OF EPITHELIAL TRANSFORMATION DURING AMPHIBIAN INTESTINAL REMODELING - IMMUNOHISTOCHEMICAL DETECTION OF INTESTINAL FATTY-ACID-BINDING PROTEIN

To determine whether the remodeling of the well-organized intestinal e pithelium during amphibian metamorphosis is regionally regulated along the anteroposterior axis of the intestine, we raised a polyclonal ant ibody against the Xenopus laevis intestinal fatty acid-binding protein (IFABP), which is known to be specifically expressed in intestinal ab sorptive cells, and examined immunohistochemically the differentiation , proliferation, and apoptosis of the epithelial cells throughout X. l aevis small intestine. During pre- and prometamorphosis, IFABP-immunor eactive (ir) epithelial cells were localized only in the anterior half of the larval intestine. At the beginning of metamorphic climax, apop totic cells detected by nick end-labeling (TUNEL) suddenly increased i n number in the entire larval epithelium, concurrently with the appear ance of adult epithelial primordia. Subsequently, the adult primordia in the anterior part of the intestine developed more rapidly by active cell proliferation than those in the posterior part, and replaced the larval epithelial cells earlier than those in the posterior part. IFA BP-ir cells in the adult epithelium were first detectable at the tips of newly formed folds in the proximal part of the intestine. Thereafte r, IFABP expression gradually progressed both in the anteroposterior d irection and in the crest-trough direction of the folds. These results suggest that developmental processes of the adult epithelium in the X . laevis intestine are regionally regulated along the anteroposterior axis of the intestine, which is maintained throughout metamorphosis, a nd along the trough-crest axis of the epithelial folds, which is newly established during metamorphosis. Furthermore, the regional differenc es in IFABP expression along the anteroposterior axis of the intestine were reproduced in organ cultures in vitro. In addition, IFABP expres sion was first down-regulated and then reactivated in vitro when the a nterior part, but not the posterior part, of the larval intestine was treated With thyroid hormone (TH) for extended periods. Therefore, it seems that, in addition to TH, an endogenous factor(s) localized in th e intestine itself with an anteroposterior gradient participates in th e development of the adult epithelium during amphibian metamorphosis. (C) 1997 Academic Press.