CELL-SPECIFIC AND SPATIOTEMPORAL EXPRESSION OF INTESTINAL FATTY-ACID-BINDING PROTEIN GENE DURING AMPHIBIAN METAMORPHOSIS

Intestinal fatty acid-binding protein (IFABP) gene is known to be regu lated during Xenopus metamorphosis. To determine the relationship betw een its regulation and cellular differentiation during metamorphosis, we have examined the distribution of IFABP mRNA in the Xenopus digesti ve tract by in situ hybridization techniques. Throughout all stages ex amined, transcripts of IFABP gene were observed exclusively in absorpt ive epithelial cells of the small intestine, and they decreased in amo unt towards the posterior intestine. Around stage 58, just before meta morphic climax, IFABP mRNA level began to decrease in larval absorptiv e cells that still remained intact morphologically. Thereafter, IFABP mRNA was no longer detected among larval cells. In turn, at stage 62, IFABP mRNA became detectable in some of the newly formed adult epithel ium that had not yet developed a brush border, but not in the remainin g larval cells. By the end of metamorphosis, IFABP mRNA became more ab undant towards the crest of intestinal folds. These results suggest th at IFABP gene expression is specific for absorptive epithelial cells o f the small intestine and is regionally regulated along the intestinal anterior-posterior axis in both tadpoles and frogs and also along the trough-crest axis of frog intestinal folds. In addition, our present study directly shows that IFABP mRNA level decreases in larval absorpt ive cells but increases in adult ones during metamorphosis, preceding morphological changes of both types of cells. Therefore, the regulatio n of IFABP gene is an early event during both larval epithelial cell d eath and adult epithelial cell differentiation.