Biology Reference
In-Depth Information
Fig. 4.2 a-d: schematic representation of the nuclear and centriole-centrosome cycle within the
first embryonic cell cycle. a Sperm aster formation from the sperm-derived proximal centriole-
centrosome complex; DNA and the nuclear matrix protein NuMA are localized in the nucleus;
b duplication of centrioles at pronuclear stage; c duplicated centriole-centrosome complex
separates and migrates around the zygote nucleus, relocating to opposite poles to form the centers
of the mitotic spindle poles; NuMA becomes a centrosome-associated protein and participates in
the formation of the spindle poles by forming a crescent around the centrosome area facing
chromosomes; d mitosis of the first cell cycle
2011a
,
2011c
); synchronized centrosome and nuclear maturation within the fer-
tilized oocyte is critical for all subsequent cell divisions within the developing
embryo. Nuclear-centrosome cell cycle synchronization has been studied in detail
for the S phase in somatic cells which correlates to the pronuclear stage in the
zygote embryo cell and to the S phases of all cells in the developing embryo when
synchronized DNA and centrosome duplication takes place. In somatic cells,
critical regulatory processes have been identified including activation of CDK2-
cyclin E (Okuda et al.
2000
; Tokuyama et al.
2001
; Ferguson and Maller
2010
)
and other cell cycle-specific proteins (reviewed in
Chap. 8
of this topic by Fisk and
in
Chap 11
of this topic by Boutros). In addition, centrosome-related protein
degradation becomes important, as detailed in
Chap. 8
of this topic by Fisk and in
Chap. 9
of this topic by Posser and Fry.
In normal cell cycles synchronization is tightly controlled through cell cycle
checkpoints, coordinated signal transduction cascades, and several other regula-
tory processes that, while well-studied in somatic cells, remain only partly
explored in embryo cells during preimplantation development. We do know that
the maturation promoting factor (MPF) and mitogen-activated protein kinase
(MAPK) are important for nuclear maturation and both are important for regula-
tion of several cell cycle events during oocyte maturation, in the fertilized embryo
cell, and in the embryo's first cell cycle (reviewed in Fan and Sun
2004
; Snook
et al.
2011
) but we do not know details on cell cycle checkpoints and regulatory
processes that drive centrosome maturation and dispersion of nuclear proteins into
the cytoplasm for subsequent specific functions during cell cycle progression of
the first and subsequent cell cycles in embryonic cells. It is clear that synchronized
signaling of nuclear and centrosome dynamics is important to ensure accurate
participation in the mitotic process during first and subsequent cell divisions.
Studies have begun to investigate the regulation of NuMA as one of the essential
nuclear and centrosome-associated proteins important for successful fertilization
and embryonic cell divisions.
