Comparison between the distribution of 7H6 tight junction-associated antigen and occludin during the development of chick intestine.

7H6 antigen is a novel tight junction-associated protein first identified in our laboratory with a monoclonal antibody generated by immunizing mice with a bile canaliculus-rich membrane fraction obtained from adult rat liver. Although the antigen is found preferentially at the tight junction of epithelial cells in various organs in adult mammals, the relationship between 7H6 antigen and other tight junction proteins remains obscure. In the present study we examined the relationship between the immunohistochemical distribution of 7H6 antigen and occludin in chick intestinal epithelial cells during development in vivo, since occludin is the only known membrane protein composing tight junctions which is found thus far exclusively in avian tissues. 7H6 antigen was found as coarse dots along the basolateral cell membrane of intestinal epithelium in the chick embryo, whereas it was found as a fine dashed line along the cell border in the chicken. In contrast, occludin was found linearly together with ZO-1 at the cell border of intestinal epithelia both in the chick embryo and chicken. The possible significance of such different localization is briefly discussed.