Biology Reference
In-Depth Information
older and younger centrioles of a pair (perhaps the only macromolecular right
angle known in biology) were first observed (Schreiner and Schreiner
1905
).
Further evidence for centrosome patterning of cytoplasmic organization is evident
in the cell axis, a defining feature of epithelial and migrating cells discernible by a
line drawn through the nucleus, intersecting the centrosome (and Golgi) and the
apical membrane or leading edge of the cell (Van Beneden
1883
; Wilson
1925
;
Bornens
2012
). While the evidence suggests that establishment of centrosome
positioning along the cell axis is secondary to primary cues emanating from the
leading edge or apical/basal lateral membranes, its importance is nonetheless clear
for maintenance or stability of cell polarity and to anchor trafficking along the
microtubule array to and from the cell center (Luxton and Gundersen
2011
).
With the advent of electron microscopy, studies by Giants such as Irene
Manton, Keith Porter, Donald Fawcett, Daniel Mazia, and Jeremy Pickett-Heaps
firmly established the centriole and centrosome as a most elegant structural feature
of eukaryotic cells. Irene Manton (1904-1988) whose fine structure studies using
UV and electron microscopy on reproductive cells of ferns, algae and other
cryptogams, and nanoplanton gave us an early close look at the 9 ? 2 structure of
flagellar axonemes and the constant cytoplasmic organization characteristic of the
smallest of eukaryotes (Manton and Clarke
1950
; Manton
1953
; Manton and Parke
1960
). Electron microscopy also revealed extreme examples of nearly invariant
features of cytoplasmic organization relative to the basal apparatus with a constant
position of nucleus, eyespot, and other organelles seen of free-living algal cells and
the regular cortical arrays of ciliates and flagellates (Dingle and Fulton
1966
; Gull
1999
; Sagolla et al.
2006
; Paredez et al.
2011
). The value of these structural
features and those of the mitotic apparatus became widely recognized as an
indicator of evolutionary relationships (Pickett-Heaps
1975
; Stewart and Mattox
1980
). We can look to these examples to find clues to the role of the centrosome in
patterning organization of complex tissue types and the cytoplasm of mammalian
cells, in general, albeit where the regularity of structure may be less obvious.
Finally, while much is made of the dispensability of centrioles and centrosomes
for mitosis in flat worms, mutant flies, and in higher plants, it is nonetheless clear
that when centrosomes become defective or 'amplified' in disease processes such
as cancer, genomic continuity becomes comprised (Brinkley and Goepfert
1998
).
The selective pressure over nearly 2 billion years for maintaining centrioles and
centrosomes in most extant eukaryotic lineages rests on two functional attributes
of the organelle—the support of ciliogenesis to anchor cilia and flagella, and the
definition of a 'coordinate geometry' system for mitotic and cytoplasm organi-
zation. The impact of the former became clear with the recognition of the role of
defects in the primary cilium in disease processes, and that of latter is appreciated
when considering the genomic instability in cancer and the definition of the plane
of cleavage which, when centrosomes are absent, restricts specific developmental
processes to a simple body plan as seen in the acentriolar divisions of the flat worm
(Azimzadeh et al.
2012
).
I have not mentioned directly 'Lesser' or burgeoning Giants, even though
exceptional investigators abound. 'Lesser' only because Giants genuinely are
