OCCLUDIN IS CONCENTRATED AT TIGHT JUNCTIONS OF MOUSE RAT BUT NOT HUMAN GUINEA-PIG SERTOLI CELLS IN TESTES/

Occludin is the only integral membrane protein identified to date as a component of tight junctions (TJs). Here, ave examined the distributi on and expression of occludin in murine testis bearing well-developed TJ. In the adult mouse testis, occludin was concentrated at TJ strands , which are located at the most basal regions of lateral membranes of Sertoli cells. In immunoblotting, occludin showed a characteristic mul tiple banding pattern, suggesting that occludin is highly phosphorylat ed in the testis. In 1-wk-old mouse testis, occludin was distributed d iffusely at the lateral membranes of Sertoli cells, and even at this s tage, highly phosphorylated occludin was detected. With development, o ccludin gradually became concentrated at the most basal regions of Ser toli cells. The same results were obtained in rat, but unexpectedly oc cludin was not detected in human or guinea pig Sertoli cells by immuno fluorescence microscopy as well as by immunoblotting. Inasmuch as TJs are also well developed in Sertoli cells of these species, me conclude d that, at least in the testes of these species, there are some Sertol i cell-specific isoforms of occludin or other TJ-associated integral m embrane proteins that differ from occludin.