Biology Reference
In-Depth Information
Fig. 5.21 Dispermic embryos a Sperm aster of a 1-cell embryo showing pronuclear envelope
(NE) breakdown and duplicated centrioles (C). b Bipolar spindle at syngamy in a 1-cell embryo
showing a centriole at one pole. c-e Anaphase spindle in an 8-cell blastomere. c Centriole at one
pole d centriole at opposite pole. e Three supernumerary centrioles on the side of spindle—Is this
centrosomal amplification, a prelude to cancer? x8,500, x20,400, x51,000, x20,400 (Sathananthan
et al.
1999
)
5.10 Molecular Aspects
Several attempts have been made to unravel the molecular structure of somatic
centrosomes (Uzbekov and Prigent
2007
; Alieva and Uzbekov
2008
; Sathananthan
et al.
2002
; Fouquet et al.
1998
; Fuller et al.
1995
; Anderson
1999
). Biochemically
they are complex structures associated with a diversity of different proteins. The
sperm centrosome has specific regulatory proteins, such as centrin, pericentrin,
gamma tubulin, associated with disulfide bonds, sulfhydryl, and phosphates among
other molecules. The zygote centrosome containing duplicated centrioles and
maternal gamma-tubulin is further added to the PCM in the ooplasm to compose a
functional centrosome (Fig.
5.24
) when the centrosome forms the sperm mono-
aster. Both centrioles (mother and daughter) then duplicate again and move to
opposite poles establishing a bipolar spindle at syngamy, the first mitosis of the
human embryo (Fig.
5.25
). This ensures the cleavage of two equal blastomeres
completing the first cell cycle. Centrin is a universal, centrosomal protein playing a
key role in centriolar duplication; it occurs in pericentriolar material (PCM) in
fibers linking centrioles to one another. Clearly, more research is needed to
characterize the proteins associated with centrosomes, especially in gametes and
embryos.
