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Disruption of the cingulin gene does not prevent tight junction formation but alters gene expression.
Cingulin, a component of vertebrate tight junctions, contains a head domain that controls its junctional recruitment and protein interactions. To determine whether lack of junctional cingulin affects tight-junction organization and function, we examined the phenotype of embryoid bodies derived from embryonic stem cells carrying one or two alleles of cingulin with a targeted deletion of the exon coding for most of the predicted head domain. In homozygous (-/-) embryoid bodies, no full-length cingulin was detected by immunoblotting and no junctional labeling was detected by immunofluorescence. In hetero- and homozygous (+/- and -/-) embryoid bodies, immunoblotting revealed a Triton-soluble, truncated form of cingulin, increased levels of the tight junction proteins ZO-2, occludin, claudin-6 and Lfc, and decreased levels of ZO-1. The +/- and -/- embryoid bodies contained epithelial cells with normal tight junctions, as determined by freeze-fracture and transmission electron microscopy, and a biotin permeability assay. The localization of ZO-1, occludin and claudin-6 appeared normal in mutant epithelial cells, indicating that cingulin is not required for their junctional recruitment. Real-time quantitative reverse-transcription PCR (real-time qRT-PCR) showed that differentiation of embryonic stem cells into embryoid bodies was associated with up-regulation of mRNAs for several tight junction proteins. Microarray analysis and real-time qRT-PCR showed that cingulin mutation caused a further increase in the transcript levels of occludin, claudin-2, claudin-6 and claudin-7, which were probably due to an increase in expression of GATA-6, GATA-4 and HNF-4alpha, transcription factors implicated in endodermal differentiation. Thus, lack of junctional cingulin does not prevent tight-junction formation, but gene expression and tight junction protein levels are altered by the cingulin mutation.[1]References
- Disruption of the cingulin gene does not prevent tight junction formation but alters gene expression. Guillemot, L., Hammar, E., Kaister, C., Ritz, J., Caille, D., Jond, L., Bauer, C., Meda, P., Citi, S. J. Cell. Sci. (2004) [Pubmed]
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