Control Systems in the Living World - Building the Most Complex Structure on Earth - page 36

of the two mother centrioles starts growing a daughter centriole perpendicularly to
itself ( Figure 1.21 ).
Both centrioles are connected through interconnecting fibers. The mother cen-
triole is distinguished from the daughter centriole by distal and subdistal append-
ages. The centrosomal material consists of a fibrous scaffolding lattice with a large
amount of coiled-coil centrosome proteins, and the centrosome's three-dimensional
architecture is primarily maintained through specific protein-protein interactions.
Microtubules are anchored with their minus ends to the centrosome core structure
and microtubule growth is regulated by distal plus-end addition of tubulin subunits
( Schatten and Sun, 2009 ).
Centrioles regulate the size of centrosomes ( Conduit et al., 2010 ). Based on their
biological role, centrosomes are also known as MTOCs. In animal cells, they are
crucial to the spindle orientation and genome stability ( Bornens, 2012 ).
Despite the dominant role that centrioles play in organizing the cytoskeleton, cells
that lack centrioles are also known, a fact that suggests the existence of concurrent
mechanisms ( Moutinho-Pereira et al., 2009 ) of spindle formation (i.e., noncentriolar
MTOCs. In higher plants, it is the nuclear envelope that acts as an MTOC for micro-
tubule nucleation and formation of spindle poles.
During cell division, the centrioles separate and migrate to opposite poles of a
cell and function as centers for spindle microtubule organization. Centrioles are also
associated with the organization and development of undulapodia (cilia and flagella).
They move to the periphery of the cell and act as basal bodies. Preexisting centrioles
can replicate to form two pairs, one for each daughter cell.
Centrioles can move away from the middle of the cell and migrate to the periph-
ery of the cell to convert into basal bodies (kinetosomes) ( Figures 1.22 and 1.23 ).
In the formation of cilia and flagella, the actin cytoskeleton plays the primary role
( Vaughan and Dawe, 2011 ), as is indicated by the fact that pharmacological inhibi-
tion of actin impairs migration and the anchoring of mature basal bodies to the apical
cell surface and formation of normal cilia ( Boisvieux-Ulrich et al., 1990 ). In the cell
membrane, the mother centriole converts to the basal body at the basis of a cilium
and the basal body triplet microtubules transform into doublet microtubules of the
axoneme ( Kobayashi and Dynlacht, 2009 ) of cilia and flagella ( Figure 1.22 ).
In 1991, one century after Boveri's theory of paternal inheritance of the centro-
some in the round worm and sea urchin, Sathananthan et al. found that in human
zygote, the paternal centrosome is functional alone ( Sathananthan et al., 1991, 1996 ).
In the soil nematode worm Caenorhabditis elegans , the paternal centriole is responsi-
ble for the asymmetric first zygote division and the varying fates of the resulting cells.
Sperm centrioles play the key role in the asymmetric division of the zygote and in the
following divisions, thus determining different cell fates ( Vaughan and Dawe, 2011 ).
Can the Cytoskeleton Compute?
The cytoskeleton, and especially microtubules and actin filaments, are essential for
nuclear processes taking place during the mitotic and meiotic divisions. They are also