In vivo imaging of tight junctions using claudin-EGFP transgenic medaka

Tight junctions (TJs) function as a physiological barrier between epithelial and endothelial sheets by restricting the diffusion of fluid through the intercellular space. Recent morphological studies associated with TJs have revealed that the TJ is a dynamic rather than a static structure; indeed, several in vitro studies indicate that proper TJ function requires dynamic TJ behavior. Direct observation of the dynamic behavior of TJs is necessary to understand the essential roles of TJs in physiological contexts, such as during embryogenesis and metastasis. Here we describe a protocol for the generation of transgenic medaka (Oryzias latipes) that express claudin–EGFP. This fluorescent fusion protein enables real-time imaging of TJs in the living embryo. Claudin–EGFP transgenic medaka will be a useful tool to screen for mutations and for small molecules affecting cell–cell adhesion.