The ciliary transition zone functions in cell adhesion but is dispensable for axoneme assembly in C. elegans.
Bottom Line: Previous work in Caenorhabditis elegans identified two ciliopathy-associated protein complexes or modules that direct assembly of transition zone Y-links.Co-inhibition of all three modules completely disrupted transition zone structure.Surprisingly, axoneme assembly was only mildly perturbed.
Affiliation: Max F. Perutz Laboratories, University of Vienna, Vienna Biocenter (VBC), A-1030 Vienna, Austria.Show MeSH
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Mentions: We next examined the consequences of transition zone perturbations on cilia assembly. A commonly used method to assess cilia integrity in C. elegans is the dye-fill assay, which monitors uptake of the lipophilic dye DiI (Inglis et al., 2007). This dye is taken up by a subset of ciliated neurons (12 amphid neurons in the head, 4 phasmid neurons in the tail) through their exposed ciliated endings and accumulates in their cell bodies. Defective dye-filling (Dyf) is often indicative of compromised cilia structure. As previously reported for other transition zone mutants (Williams et al., 2008, 2011), ccep-290 mutants individually did not display significant dye-fill defects. However, double mutants with either nphp-1 or nphp-4 were strongly Dyf. In contrast, no genetic interactions were detected with mksr-2. Dye-filling was restored by expression of the appropriate GFP transgene, confirming specificity of the mutant phenotypes and functionality of our GFP reporters (Fig. S1 H; Fig. S2, D and E; and not depicted). These results would appear to support a role for the transition zone in cilia assembly. However, direct visualization of phasmid cilia using the IFT marker CHE-11:GFP failed to reveal any major defects. Most strikingly, ∼83% of cilia were found to remain in ccep-290;mksr-2;nphp-4 triple mutants in which all three transition zone modules are inhibited (Fig. 2, A and B). Cilia lengths (Fig. 2 C) and IFT rates (Fig. 2 D, E) were also largely normal. Ciliary ultrastructure was also unaffected with the exception of occasional displaced doublet microtubules, likely reflecting disorganization within the transition zone (Fig. 2 F). We conclude that loss of transition zone structures has only mild effects on axoneme assembly and organization in C. elegans.
Affiliation: Max F. Perutz Laboratories, University of Vienna, Vienna Biocenter (VBC), A-1030 Vienna, Austria.