Biology Reference
In-Depth Information
Fig. 5.15 Functional centrosome in a fetal oogonium. The centrosome has two typical centrioles
with PCM (right), like in somatic cells. It is lost or reduced in the oocyte during oogenesis but its
fate is unknown. Is it abstricted into the first polar body during maturation? x10,500, x87,500
(Sathananthan et al.
2000
)
Fig. 5.16 Mature oocyte at metaphase II (TEM): the centrosome is absent or reduced at the
spindle poles. Microtubules terminate in the egg cortex, abruptly. Note chromosomes at the
equator and cortical granules in the cortex. x8,500, x15,400 (Sathananthan
1998
)
that nucleates MTs, thus becoming a functional centrosome. This is the forerunner
of all centrosomes in embryonic, fetal, and adult somatic cells (Sathananthan et al.
1996
). An extensive MT network is formed by the sperm aster (Fig.
5.5
), which
reorganizes the whole cytoskeleton of the oocyte soon after sperm incorporation,
as revealed by FM (Schatten
1994
; Simerly et al.
1995
). This aster is initially
directed toward the female pronucleus (FPN) and may be involved in drawing the
FPN toward the male pronucleus (MPN) to take up a more centralized position in
