Table 2.
Examples of different distal domain structures.
| Organism | Plugs | Central MT 1 Cap | Ciliary Crown | Other | References |
|---|---|---|---|---|---|
|
Chlamydomonas (green alga) Tetrahymena (body cilia, ciliate protozoa) Aequipecten (bay scallop gill) |
Plug structures are inserted into the tip of the A-tubules of the outer doublets and attached to the membrane by distal filaments | Linked to the membranes | No | [15,104,107,108] | |
|
Tetrahymena (oral apparatus cilia, ciliate protozoa) Aequipecten (certain cilia, bay scallop gill) |
Plug structures are inserted into the tip of the A-tubules of the outer doublets and attached to the central microtubule cap by distal filaments | Linked to the membranes | No | [104] | |
|
Crithidia, Herpetomonas, Trypanosoma and Leishmania (Promastigote; parasitic protozoa) |
No | No | No | Blunt end with two dense material regions, one associated with the MT central pair and the other with the doublets | [113] |
| Leishmania (Amastigote, parasitic protozoa) | No | No | No | No dense material or organized structure | [92] |
| Beroe (macrocilia, ctenophore) | No | No | No | Giant capping structure at the tip, formed by extensions of the A and central-pair MTs, bound together by amorphous material | [110] |
| Paratomella (haptocilia, flat worm) | No | No | Structure resemble crown | Asymmetrical cap structure. Some of the doublets end as a single A-microtubule, whereas for others, the A- and B-microtubules terminate in the cap. MT central pair and doublets 1, 2, 3, 8 and 9 terminate in a distal cap, whereas doublets 4 to 7 end at a dense material of a proximal secondary cap |
[103,119] |
| Caenorhabditis (sensory amphid channel, worm) | No | No | No | Tip presents only MT singlets. No cap or dense material | [111] |
| Caenorhabditis (sensory amphid wing cilia C, worm) | No | No | No | The middle region of the axoneme both contain doublets and singlets that “splay apart” laterally and end together. The tip presents a membranous fan-like structure. No cap or dense material | [111] |
| Lima (bivalve) | No | No | No | Dense material at the distal ends of the axonemal MTs | [122] |
| Periplaneta (antenna pedicel, cockroach) | No | No | No | Dilated tip, doublets become singlets and terminate in an electron-dense spheroid | [123] |
| Bombina (frog) | Plugs are inserted into the lumen of the A-tubules, attaching them to the caps | No | No | Asymmetrical cap structure. One large cap, linked to the membrane and to doublet MTs number 4 to 7, and a smaller cap linked to the doublets number 1, 2, 3, 8 and 9, as well as to the two central MTs |
[121] |
| Primary cilia (vertebrates) |
No | No | No | In distal segment doublets are converted into singlets through the loss of the B-tubule. No cap or dense material | [124] |
1 Microtubules.