Figure 3.

Procentriole microtubule triplet growth. (A) Microtubule singlet of a procentriole. The proximal part of the microtubule is capped by a conical structure. The right panel is a 3 × magnification of the boxed region. (B) Two Z sections of an A-microtubule (singlet) spaced by 5 nm. The distal part of the microtubule forms an outwardly curved extension (open arrow). (C–E) Microtubule doublets from three different tomograms. Under each panel, a schematic representation of microtubule organisation is shown: A-microtubule is in purple, B-microtubule is in red (C). The B-microtubule is 35 nm from the tip of the A-microtubule cap. (D) The B-microtubule starts at 18 nm from the tip of the A-microtubule cap and shows an outwardly curved extension at its proximal extremity (open arrow). (E) The B-microtubule is at the level of the tip of the A-microtubule cap. (F) Microtubule triplet of a procentriole. The C-microtubule is attached to the side of the B-microtubule at a distance of 46 nm from the distal tip of the cap. The distal and proximal extremities of the C-microtubule display curved extensions (open arrows). (G) Microtubule triplet of a mature centriole. The microtubules are opened at their distal and proximal extremities. (F, G) Next to the panel, a schematic representation of microtubule organisation is shown: A-microtubule is in purple, B-microtubule is in red, and C-microtubule is in green. Scale bar: 20 nm.