Biology Reference
In-Depth Information
Fig. 5.5 Rhesus fertilization after ICSI (fluorescent microscopy). The sperm aster (left)is
associated with the centrosome associated with the male pronucleus (M). The female pronucleus
(F) is attracted to the male but has not decondensed yet. The first mitotic bipolar spindle (right)
shows chromosomes at metaphase. Note distinct sperm tail in both fluorescent images. The
monkey is similar to the human in centrosomal inheritance and dynamics, like most animals are
(Courtesy Dr. Laura Hewitson, USA)
5.4 Gamete Centrosomes
Only one functional centrosome is required in either gamete for normal fertil-
ization and embryo development. It is either the paternal (as in humans and most
other animals) or maternal (as in rodents such as mice). Therefore, there is a
reduction or inactivation of the centrosome in one of the gametes—sperm or egg.
Those with dominant paternal centrosomes obey Boveri's rule of centrosomal
inheritance postulated in 1890 (Boveri
1900
), while rodents present the exception
to the rule where the maternal centrosome is dominant (Schatten
1994
). Humans
and most other animals (including sea urchins, roundworms, and farm animals)
follow Boveri's rule with respect to centriole inheritance and dynamics during
early development (Sathananthan et al.
1991
,
1996
; Sathananthan
1997
)
5.5 The Paternal Centrosome (Centriole)
In humans, the sperm centrosome also shows partial reduction during spermio-
genesis, when round spermatids metamorphose into motile sperm cells (Satha-
nanthan et al.
1996
,
2001
; de Kretser and Kerr
1994
; Holstein and Roosen-Runge
1981
; Manandhar et al.
2000
). The round spermatid contains two centrioles in the
centrosome complex, like most other somatic cells, while the mature sperm cell
has only one centriole—the proximal (PC) concealed in a 'black box' in the sperm
neck (connecting piece) beneath the basal plate (Figs.
5.7
,
5.8
,
5.9
,
5.10
,
5.11
,
5.12
,
5.13
,
5.14
). The distal centriole (DC) is committed to the formation of the
flagellar axoneme in the elongated spermatid and is reduced to a vestige in mature
