Absence of the tight junctional protein AF-6 disrupts epithelial cell–cell junctions and cell polarity during mouse development

Background: The establishment, maintenance and rearrangement of junctions between epithelial cells are extremely important in many developmental, physiological and pathological processes. AF-6 is a putative Ras effector; it is also a component of tight and adherens junctions, and has been shown to bind both Ras and the tight-junction protein ZO-1. In the mouse, AF-6 is encoded by the Af6 gene. As cell–cell junctions are important in morphogenesis, we generated a null mutation in the murine Af6 locus to test the hypothesis that lack of AF-6 function would cause epithelial abnormalities. Results: Although cell–cell junctions are thought to be important in early embryogenesis, homozygous mutant embryos were morphologically indistinguishable from wild-type embryos through 6.5 days post coitum (dpc) and were able to establish all three germ layers. The earliest morphological abnormalities were observed in the embryonic ectoderm of mutant embryos at 7.5 dpc. The length of the most apical cell–cell junctions was reduced, and basolateral surfaces of those cells were separated by multiple gaps. Cells of the embryonic ectoderm were less polarized as assessed by histological criteria and lateral localization of an apical marker. Mutant embryos died by 10 dpc, probably as a result of placental failure. Conclusions: AF-6 is a critical regulator of cell–cell junctions during mouse development. The loss of neuroepithelial polarity in mutants is consistent with a loss of efficacy of the cell–cell junctions that have a critical role in establishing apical/basolateral asymmetry.