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F O R P H Y S I C I A N S – resources
Concluding comments
In many respects, studies of the mitochondria in early
mammalian development have raised more questions than
have been definitively answered, although their long
known role in ATP production in the oocyte and embryo
remains intact. Issues related to complement size, spatial
distribution, fine structural organization, mtDNA integrity
and copy number, high and low polarity, participation in
ionic regulation and inheritance patterns offer promising
leads for additional investigation and possible applications
in clinical IVF. In particular, study of their stage-specific
reorganization and association with other cytoplasmic
components such as the SER should determine whether
they are (a) directly involved in the focal or global cytoplasmic
activities that determine normal competence or
result in demise and (b) which of their many nonrespiratory
functions in somatic cells also pertain to the oocyte
and preimplantation-stage embryo. Continued research
will also yield the type of basic scientific information that
will be necessary to demonstrate that controversial procedures
applied to certain infertile women, such as donor
ooplasmic transfusion (Cohen et al. 1997), actually treat
mitochondrial defect(s) that have been assumed to occur
in the recipient oocyte and are associated with cleavagestage
demise (Brenner et al. 2000, Brenner 2004). Clinicians
and patients need to know whether these or other
similar manipulations (e.g. direct mitochondrial transfer,
Van Blerkom et al. 1998) are safe for the intended child
and can, therefore, be used effectively in the treatment of
infertility or to ‘correct’ oocytes with known mtDNA
defects, such as those associated with OXPHOS diseases
(Brenner 2004, Cummins 2004, St. John et al. 2004).
Although anticipated, whether mitochondrial research will
also yield methods that can be used routinely in the clinical
IVF laboratory to select for high competence oocytes
and early embryos remains to be determined.
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