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J. Cell Biol.,
Volume 141, Number 2, April 20, 1998 397-408


* Department of Cell Biology, Occludin is the only known integral membrane protein of tight junctions (TJs), and is now believed to be directly involved in the barrier and fence
functions of TJs. Occludin-deficient embryonic stem
(ES) cells were generated by targeted disruption of
both alleles of the occludin gene. When these cells were
subjected to suspension culture, they aggregated to
form simple, and then cystic embryoid bodies (EBs)
with the same time course as EB formation from wild-type ES cells. Immunofluorescence microscopy and
ultrathin section electron microscopy revealed that polarized epithelial (visceral endoderm-like) cells were
differentiated to delineate EBs not only from wild-type
but also from occludin-deficient ES cells. Freeze fracture analyses indicated no significant differences in
number or morphology of TJ strands between wild-type
and occludin-deficient epithelial cells. Furthermore,
zonula occludens (ZO)-1, a TJ-associated peripheral
membrane protein, was still exclusively concentrated at
TJ in occludin-deficient epithelial cells. In good agreement with these morphological observations, TJ in occludin-deficient epithelial cells functioned as a primary
barrier to the diffusion of a low molecular mass tracer
through the paracellular pathway. These findings indicate that there are as yet unidentified TJ integral membrane protein(s) which can form strand structures, recruit ZO-1, and function as a barrier without occludin.
Department of Anatomy, Faculty of Medicine, Kyoto University, Sakyo-ku, Kyoto 606, Japan; § Second Department of Internal Medicine, Osaka University Medical School, Suita, Osaka 565, Japan;
Department of Anatomy
and Cell Biology, Gunma University School of Medicine, Showa-machi, Maebashi 371, Japan; ¶ Department of Cell Biology,
Cancer Institute, Toshima-ku, Tokyo 170, Japan; and ** Department of Molecular Genetics, Tohoku University School of
Medicine, Sendai 980, Japan
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