Developmental expression of the tight junction protein, occludin, in the gastrointestinal tract of the chick embryo

Abstract

 The developmental expression of occludin was studied biochemically in whole chick embryos to determine when intercellular tight junctions develop. Occludin mRNA was first detected after 3 days of incubation by the reverse transcriptase-polymerase chain reaction. On northern blot analysis, although occludin mRNA was not discernible in 3-day-old embryos, weak but clear expression was noted on day 4 of incubation and increased dramatically in 5-day-old embryos. Occludin was not detectable on days 3 or 4 of incubation by western blot analysis, and was first detected in 5-day-old embryos. In addition, the expression of occludin was examined immunohistochemically in the gastrointestinal tract of 3- to 21-day-old embryos. Immunoreactivity for occludin was not expressed on day 3 of incubation. On day 4 of incubation, weak immunoreactivity was demonstrated in the gastrointestinal tract, and gradually became stronger with development. By day 11 of incubation, a positive immunoreaction was obtained only on the apical surfaces of the epithelial cells, i.e., at the junctional complexes, while weak immunoreactivity was diffusely distributed throughout the epithelial cells. The possible roles of occludin in the developing gastrointestinal tract are discussed.