Figure 1.

Centriole/basal body positioning in polarized epithelial cells. A and B: Epithelial cells are like prisms with a belt of proteins connecting adjacent cells. These proteins form adherens junctions (AJ) in Drosophila (A) and AJ and tight junctions (TJ) in vertebrates (B). AJ or AJ/TJ are responsible for delimiting the apical and basal membrane domains in polarized epithelial cells. Centrioles, in polarized epithelial cells, are localized in the most apical planes (A and B). B: In a ciliated epithelium, centrioles migrate towards the apical membrane, where they contact the apical membrane becoming the “basal bodies”/BB, from which the cilia form and protrude into the apical space. C: Certain epithelia display a tissue-coordinated off-center positioning of BBs/centrioles, but still within the most apical planes. This is also observed in many multiciliated epithelia (bottom graph). D: In more specialized epithelial cells, like the outer and inner sensory hair cells (OHC and IHC) in the organ of Corti, the primary cilium, called kinocilium here, is also polarized in an off-center position in the apical plane, subsequently organizing an actin based V-shaped structure, the stereocilia bundle, which follows the polarization of the kinocilium.