Metamorphosis‐associated and region‐specific expression of calbindin gene in the posterior intestinal epithelium of Xenopus laevis larva

The present study used a molecular approach toward understanding the mechanism of hormone- and region-dependent remodeling of the small intestine during metamorphosis of Xenopus laevis. A protein spot was noticed on a two-dimensional polyacrylamide gel as a protein whose expression was metamorphic stage- and region-dependent. The protein was identified as the Xenopus homolog (Xcalbindin) of chick calbindin D28k. Xcalbindin expression in the intestine was restricted to absorptive cells in the posterior part, being detectable at stages 49-61, not detectable at stages 62-63, detectable again at stages 64-66, and finally becoming undetectable in the adult. During spontaneous metamorphosis, the level of Xcalbindin mRNA was significantly increased between stages 57 and 58, dramatically reduced at stage 59, and the mRNA was undetectable from stages 60-63, after which it was weakly re-expressed until the end of metamorphosis. Such up- and down-regulation of Xcalbindin mRNA was induced precociously by exogenous thyroid hormone. These results indicated that Xcalbindin is a specific marker of the differentiated absorptive cells of the intestine. Immunohistochemistry with specific antibodies against Xcalbindin demonstrated that precursor cells of adult intestinal epithelial cells expressed Xcalbindin. Considering these results, the origin of adult intestinal epithelial cells was discussed.