Biology Reference
In-Depth Information
Fig. 20.3 Schematic representation of the origin of paternal centriole and maternal centrosomal
proteins (such as c-tubulin and pericentrin) and their role in reconstitution of the functional
centrosome during fertilization events
functions, but similar transformation of centrosomes occurs during fertilization.
The other milestone in centrosome research in Xenopus laevis cell-free system was
the discovery that the MT self-assembly is sufficient to organize the bipolar structure
of the spindle (Heald et al.
1996
,
1997
). These studies, in which the artificial
chromosomes (beads covered by plasmid DNA) were used, demonstrated that the
kinetochores, the complex chromosomal structures physiologically assuring MT
attachment, are not necessary for the proper spindle assembly. Studies on mouse
oocytes deprived of chromosomes showed that bipolar spindles may form also in the
total absence of chromatin. This happens through the MT self assembly with the help
of motor proteins organizing both MTs and PCM first into asters and then into
spindle-like structures (Brunet et al.
1998
). All these experiments indicate that
centrioles and even chromosomes are dispensable for spindle assembly both in
Xenopus laevis cell-free extracts and, under special conditions, in living cells of
different species (Walczak et al.
1998
; Varmark
2004
). The optional character of
the presence of centrioles was also confirmed in HeLa cells in which centriole
disassembly was induced by a monoclonal antibody GT335 directed against
glutamylated tubulin (Bobinnec et al.
1998
). In these cells, the centriole disappear-
ance had a severe impact on the structure of centrosome and resulted in the
disaggregation of PCM.
