Tissue Engineering And Nanotheranostics

“9.61x6.69” b2815 Tissue Engineering and Nanotheranostics

Delivering Nanoparticles to Cancer Cells 215

Once established upon and across the C microtubule the Plk4

recruits SAS6, a protein forming the structural base for the growth of

a new centriole: Specifically, the SAS6 protein then emits nine radial

spokes angled at 40° to each other where each spoke provides support

for the growth of a triplet of microtubules — thus forming a micro­

tubule blade of the newly growing centriole.

The conventional understanding13–28 for the growth of the micro­

tubules, and thus also of the centrioles, is that the a /b tubulin dimers

are recruited to the SAS6 spokes by a γ­tubulin protein. The SAS6

spokes provide platforms for triplets of γ­tubulin rings. These rings

have a series of 13 pores through which the a /b dimers are recruited

from the MTOC and pushed upward to form microtubule filaments.

Figure 9 provides a sketch of the envisioned γ­tubulin ring together

with its pores.

The pores used for inserting a /b tubulin are sometimes called the

“γ­tubulin small complex” (γ­Tu–SC).

Interestingly, the γ­tubulin ring is not quite planar. Instead, its

ends overlap so that it has the form of a lockwasher. This in turn

causes the microtubule filaments to be inclined at a small angle.

The centriole host is known as the “mother” and the growing

centriole via the growing microtubules is known as the “daughter”.

In the original mother­daughter centriole pair, each centriole hosts a

new centriole. The mother has a new daughter, and the daughter has

a daughter of its own — a “granddaughter”.

The microtubules of a daughter grow to only about 80% of the

length of the mother’s microtubule.

Fig. 9. A γ­Tubulin ring complex (γ­Tu–RC).