Generation of transgenic medaka expressing claudin7-EGFP for imaging of tight junctions in living medaka embryos.

The tight junction (TJ) is a specialized cell-cell adhesion structure in epithelial and endothelial sheets unique to the chordates and functions as a barrier of fluidal diffusion across the cell sheets. In order to study the dynamics of TJ formation in vivo during embryogenesis, we have generated a transgenic medaka line that expresses claudin-7 protein fused to enhanced green fluorescent protein under the regulation of the red seabream beta-actin promoter in transparent medaka embryos. Claudins contain four transmembrane domains and have been identified as the key molecules that dictate the function of TJs. This transgenic medaka line will thus be useful for imaging of TJs in living embryos and hence in screening for mutations affecting cell-cell adhesion.