Molecular architecture of the transition zone and function in cell adhesion. (A) 3D reconstruction model of the transition zone in C. elegans, highlighting key features. See also Video 2. Based on protein localization and mutant phenotypes, CCEP-290 is an essential component of the central cylinder (this study), whereas MKS and NPHP module components function in assembly of Y-links (Williams et al., 2011). Transition zone mutants display no apparent defects in axoneme assembly. However, ciliary gating and cell adhesion are compromised. (B) The dendrite of C. elegans amphid and phasmid neurons forms by retrograde extension, with the cell body moving backward while the dendritic tip remains in place. The transition zone mediates tip anchorage via interactions with the extracellular matrix. (C) Positioning of the primary cilium determines cell fate in vertebrate neuroepithelium. Cells with apically positioned cilia maintain their position at the apical adherens junction belt, whereas cells with basolateral cilia delaminate (Wilsch-Bräuninger et al., 2012; Paridaen et al., 2013). Differential signaling, but also mechanical anchorage by the cilium, could explain this result.