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. 2020 Sep 20;39(22):e106249. doi: 10.15252/embj.2020106249

Figure 6. Working model of centriolar cartwheel architecture.

Figure 6

  1. Occurrence of CID or fCID in species analyzed in this study (T. spp., T. agilis, and T. mirabilis, blue background), and in select other organisms (not to scale), mapped on a taxonomic tree generated using phyloTv2 based on NCBI taxonomy—https://phylot.biobyte.de/. See Discussion in main text for references.
  2. Schematic of cartwheel hub in T. spp. and T. agilis with 9‐fold symmetrical CID (gray) connecting to the hub, equidistant between two spokes.
  3. The CID (dark gray) in T. spp. and T. agilis is polarized distally relative to the hub element comprising two tightly superimposed ring elements—shown in different colors for clarity.
  4. Schematic of cartwheel hub in T. mirabilis with continuous fCID (dark gray) along the proximal–distal axis, with potential thin connections to the hub, equidistant between two spokes.
  5. Working model of cartwheel stacking, with alternation of two modes of SAS‐6 ring stacking: Pairs of rings are tightly superimposed with a rotational offset (dashed line), and such offset double rings are then stacked in register (solid line); the offset direction is consistent in T. spp., T. agilis, and T. mirabilis, yet may be different in other species, as shown in Paramecium (Klena et al, 2020). Surface representation of SAS‐6 rings in different colors for clarity; homodimers highlighted by black contour.
  6. Consensus model of periodicities in centriolar cartwheel along the proximal–distal axis. Surface representation of offset double rings tightly superimposed with ˜3.2 nm periodicity, in register with the next such offset double ring located ˜5.2 nm away, thus amounting to an overall periodicity of ˜8.4 nm. Note that these values are based on the T. mirabilis 36% class, which has the most clearly resolved periodicities, yet does not have a CID as shown in this composite model, with related values in other species; see text for details. The CID also exhibits ˜8.4 nm mean periodicity in the two Trichonympha species. Two spoke periodicities are observed: close to the hub, pairs of spokes are ˜8.4 nm apart, whereas spoke pairs merge toward the periphery, where their periodicity is hence ˜16.8 nm, matching that of the pinhead and connected microtubules. Note that spoke angles are merely illustrative and limited by the resolution of the available STA maps. Note also that alternative modes of spoke merging may be revealed by analyzing much larger sub‐volumes and may be present in other species (Klena et al, 2020).