Assembly of tight junctions during early vertebrate development

Tight junction formation during development is critical for embryonic patte rning and organization. We consider mechanisms of junction biogenesis in cl eaving mouse and Xenopus eggs. Junction assembly follows the establishment of cell polarity at 8-cell (mouse) or 2-cell (Xenopus) stages, characterize d by sequential membrane delivery of constituents, coordinated by embryonic (mouse) or maternal (Xenopus) expression programmes. Cadherin adhesion is permissive for tight junction construction only in the mouse. Occludin post -translational modification and membrane delivery, mediated by delayed ZO-1 alpha(+) isoform expression in the mouse, provides a mechanism for complet ion of tight junction biogenesis and sealing; regulating the timing of blas tocoel cavitation.