Biology Reference
In-Depth Information
Fig. 1.1 Models for duplication a Yeast spindle pole bodies (SPB Duplication); the half bridge
of the preexisting (mother) SPB serves as a template and nucleation site for the new (daughter)
SPB that is formed in parallel. b Centriole Duplication; the new (daughter) centriole is formed
perpendicularly to the preexisting (mother) centriole and at a significant distance from the surface
of the preexisting centriole
ensure that only a single new structure is formed. Centrosomes consist of two
centrioles surrounded by PCM. Centrosome duplication starts after the two pre-
existing centrioles separate slightly and a new centriole forms near each of the
preexisting centrioles. Centrosome duplication is concluded when each centriole
pair completely separates, along with some of the PCM of the original centrosome.
In each centrosome, the older centriole is also known as the mother centriole and
the new centriole is known as the daughter centriole.
The process of centrosome duplication is conceptually similar to how DNA and
yeast SPB duplicate (Fig.
1.1
). DNA duplication starts by splitting into two strands,
which then serve as a template to create a new strand. Yeast SPB duplicate by
splitting into two halves. Each half contains a structure known as the half bridge,
which then serves to template the formation of another half bridge (Jaspersen and
Winey
2004
; Jones and Winey
2006
). Since, like DNA and SPB duplication, cen-
trosome duplication maintains one preexisting element and creates one new element,
it is thought that centrosomes duplicate in a semi-conservative manner.
Although many of the proteins involved in centrosome duplication have been
recently identified, the critical question of how the centrioles duplicate remains
elusive. Very little is known about the overall mechanism of centriole duplication
(Azimzadeh and Marshall
2010
; Nigg and Raff
2009
). It has become increasingly
accepted that centriole duplication does not involve a templating mechanism like
in DNA and SPB duplication.
Several lines of observation suggest that de novo formation of the new cen-
trioles takes place at the vicinity of the preexisting centriole.
i) The new centriole is formed perpendicularly to the preexisting centriole.
ii) The new centriole forms at a distance of about 30 nm from the surface of the
preexisting centriole (Anderson and Brenner
1971
; Phillips
1967
),
iii) The new centriole can have a very different structure from the preexisting
centriole (Phillips
1967
).
iv) Under certain conditions, centrioles can form in the absence of a preexisting
centriole (Fulton and Dingle
1971
; Rodrigues-Martins et al.
2007b
)
v) Several new centrioles can be induced to form simultaneously around the
preexisting centriole by overexpressing centriolar components (Kleylein-Sohn
et al.
2007
).
