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centrosomal incompatibilities are provided in our more detailed previous review
on SCNT (Schatten and Sun
2009a
).
The case may be made that in the 10 times smaller somatic cell the require-
ments for somatic (donor) cell centrosomes are likely to be different compared to
those in the huge reconstructed egg of about 100 lm. We know from somatic cell
studies that microtubule lengths and numbers are regulated by changes in c-tubulin
recruitment to the centrosome (reviewed in Schatten
2008
). As the sperm con-
tributes only a small amount of c-tubulin to the regular fertilization process most
of the c-tubulin components come from the oocyte after fertilization. We do not
yet have detailed information on the recruitment of c-tubulin from the oocyte to
the somatic cell centrosome complex which may differ from recruitment to the
sperm centrosome during normal fertilization resulting in abnormal microtubule
formations in SCNT reconstructed eggs.
While we do not yet know the underlying causes for centrosomal abnormalities
in SCNT reconstructed embryos, our knowledge of nuclear reprogramming has
increased in recent years (reviewed in Prather
2000
; Sun and Schatten
2007
;
Schatten and Sun
2009a
) and we now have indications that nuclear matrix dys-
functions may play a role in the low success rate following SCNT, as nuclear
matrix dysfunctions impacts DNA replication (reviewed by Yamauchi
2011
) and it
may also impact centrosome functions. As NuMA is part of the nuclear matrix,
NuMA-derived spindle abnormalities have been reported for cancer cells (Kam-
merer et al.
2005
); NuMA dysfunctions may be among the reasons for the mul-
tipolar spindle pole formations that we find in SCNT porcine embryo cells (Zhong
et al.
2007
).
To study the contributions of spindle pole centrosomal components in SCNT
eggs, Zhong et al. (
2005
) used intraspecies and interspecies SCNT reconstructed
eggs to determine specific centrosomal components that are contributed by the
donor cell centrosome complex and the donor cell nucleus. This study used mouse
MII oocytes as recipients, mouse fibroblasts, rat fibroblasts, or porcine granulosa
cells as donors to produce intraspecies and interspecies nuclear transfer embryos.
Specifically, to study NuMA dynamics in SCNT reconstructed eggs, a specific
NuMA antibody was employed that did not recognize NuMA protein of mouse
oocytes but recognized NuMA in porcine granulosa cells, thereby being able to
distinguish NuMA contributed by the oocyte and donor. The results clearly
showed that NuMA was localized to the donor cell nucleus and was translocated
out of the nucleus into the cytoplasm followed by translocation to the mitotic
spindle poles where donor cell NuMA participated in spindle pole formation
during first mitosis in SCNT eggs. Further analysis of NuMA translocation out of
the nucleus in porcine SCNT eggs (Liu et al.
2006
) revealed that NuMA was
contributed by fetal fibroblast donor cells to reconstructed porcine eggs and it took
about 6 h after nuclear transfer before NuMA could be visualized with immuno-
fluorescence microscopy, indicating a lag period for NuMA reprogramming by the
reconstructed egg which is significantly longer than NuMA detection in decon-
densing sperm nuclei that takes place within minutes after fertilization (Liu et al.
2006
). This study concluded that cytoplasmic factors in the recipient porcine
