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Abstract
Germinal vesicle transplantation (GVT) has been proposed
as a possible treatment through which to correct
age-related oocyte aneuploidy caused by dysfunctional
ooplasm. How healthy ooplasm regulates normal meiosis and
subsequent development has yet to be elucidated, but
impaired mitochondrial metabolism may be attributable to
incomplete segregation of the oocyte chromosomes. In this
study, after ooplasmic mitochondrial damage by
photoirradiating chloromethyl-X-rosamine, examination of
the oocyte nuclei's ability to survive after transfer into
healthy ooplasts was carried out. To assess their
fertilizability and potential for development, GVT oocytes
were fertilized by ICSI and transferred to foster mice.
Condition of the offspring at birth was assessed and
epigenetic analysis was carried out.
Photosensitization consistently inhibited oocyte
maturation. However, after GVT of photosensitized nuclei
into healthy ooplasts, 67.2% were reconstituted and 76.2%
of these matured normally, with an over all rate of 51.2%,
much higher than that (6.0%) in the
mitochondrially-injured oocytes. After ICSI, 65.8% (52/79)
of GVT oocytes were fertilized normally, and 21.1% (11/52)
eventually reached the blastocyst stage. The transfer of
132 two-cell GVT embryos into the oviducts of
pseudopregnant females, resulted in 17 apparently healthy
live offspring. For some key developmental genes, high
level of expression was identified in the GVTr-derived
fetal adnexa. Thus, one can induce in oocyte
mitochondria
a photosensitization-based type of damage which
consistently inhibits GV breakdown, meiotic spindle
formation, chromosomal segregation, and polar body
extrusion. Germinal vesicle transplanted and 'rescued'
(GVTr) oocytes were able to undergo maturation,
fertilization, embryonic cleavage, and ultimately develop
to term. This approach may provide a model in which to
study age-related ooplasmic dysfunction seen in human oocytes.
Key words:
Gamete Biology •
Fertilization •
Gene regulation •
Meiosis •
Oocyte development
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