Control Systems in the Living World - Building the Most Complex Structure on Earth - page 37

Figure 1.22 Major structural features and functions of primary cilia, basal bodies, and
centrioles. The primary cilium is comprised of a basal body, an axoneme, and the ciliary
membrane. Basal bodies are mother centrioles that have been modified by the addition of
defining accessory structures, including transition fibers, basal feet and caps, and striated
rootlets. The triplet microtubules of the basal body centriole give rise to the doublet
microtubules of the ciliary axoneme at the region of the transition zone. Centrioles are
typically found to be orthogonal pairs comprising a mother and a daughter, the former being
associated with specialized functions ( Seeley and Nachury, 2010 ).

(C)

(A) (B)

Figure 1.23 Centriole/basal body migration in terminally differentiated cells. The process of
ciliogenesis produces thousands of motile cilia on many specialized, terminally differentiated
cells. (A) Large numbers of basal bodies are formed within a single cell. Basal bodies migrate
and dock with the cell membrane. (B) Movement requires actomyosin and is regulated by
GTPase RhoA. (C) Cilia are assembled from the docked basal bodies ( Vaughan and Dawe,
2011 ).

crucially involved in determining the position of organelles and for intracellular trans-
port of vesicles and other supramolecular elements; they determine the shape of the
cell and the dynamism of the cell shape. All these functions accomplished by micro-
tubules and actin filaments are required rather than randomly occurring processes.