Spatial Control of Primary Ciliogenesis by Subdistal Appendages Alters Sensation-Associated Properties of Cilia

Abstract

Vertebrate cells can initiate ciliogenesis from centrioles at the cell center, near the Golgi, forming primary cilia confined or submerged in a deep narrow pit created by membrane invagination. How or why cells maintain submerged cilia is unclear. Here, by characterizing centriole sub-distal appendages (sDAP) in cells exclusively growing submerged cilia, we found that a group of sDAP components localize to the centriole proximal end through the cohesion factor C-Nap1, and that sDAP functions redundantly with C-Nap1 for submerged cilia maintenance. Loss of sDAP and C-Nap1 has no effect on cilia assembly, but disrupts stable Golgi-cilia association, and allows normally submerged cilia to fully surface, losing the deep membrane invagination. Intriguingly, unlike submerged cilia (stationary), surfaced cilia actively respond to mechanical stimuli with motions, and can ectopically recruit hedgehog signaling components in the absence of agonist. We propose that spatial control of ciliogenesis uncouples or specifies sensory properties of cilia.

Centriole splitting caused by loss of the centrosomal linker protein C-NAP1 reduces centriolar satellite density and impedes centrosome amplification

“…C-NAP1 nulls showed intact centriole structure, as detected by CEP135 and centrin localization, along with apparently normal pericentriolar material, as determined by staining for γ-tubulin (Figure 1, D–F). We noted a loss of ninein signal in one of the separated C-NAP1 centrioles (Figure 1F), which we attribute to the loss of ninein from the centriolar proximal ends while it was being retained at the subdistal appendages, as recently described in another C-NAP1–knockout line (Mazo et al. , 2016).…”

“…Consistent with observations knockouts generated with zinc finger nuclease (ZFN)–mediated targeting of C-NAP1 exon 14 (Panic et al. , 2015) and with a CRISPR-mediated disruption of C-NAP1 exon 20 (Mazo et al. , 2016), 30% of our C-NAP1 nulls showed a distance of ≥2 μm between G1-phase centrioles compared with 5% in wild-type cells (Figure 2, A and B).…”

“…From this result, we conclude that C-NAP1 is not required for primary cilium formation, consistent with recent knockout studies of C-NAP1 function (Panic et al. , 2015; Mazo et al. , 2016) and a previous siRNA analysis (Graser et al.…”

Hierarchical assembly of centriole subdistal appendages via centrosome binding proteins CCDC120 and CCDC68

“…15). Interestingly, a recent study reported that the loss of SDA components such as ODF2, CEP170 and Ninein change neither the length of primary cilia nor the percentage of ciliated cells, but affects the spatial configuration of cilia34. In this study, our data also showed that depletion of CCDC120 and CCDC68 changes neither the percentage of ciliated cells nor the ciliary length.…”

ALMS1 and Alström syndrome: a recessive form of metabolic, neurosensory and cardiac deficits

“…CEP250 does not seem to be required for primary cilium formation or maintenance [59, 155–157], although a recent conflicting report suggests that ciliogenesis cannot proceed if centrosome cohesion is lost [158]. Another recent study showed that CEP250 contributes to retaining the cilium in a submerged state, affecting its capacity to sense external cues [159]. CEP250 appears to be crucial for the recruitment of several proteins to centriole proximal ends, including Girdin (Girders of actin filaments) and a group of proteins that associate also with the distal region of the mother centriole (NEK2, ninein, CEP170, p150glued and KIF2A) [159–162].…”