The developmental capacity of reconstructed bovine oocytes that contained nuclei from
growing stage oocytes, 70-119 microm in diameter, was assessed after fertilization
in vitro. Nuclei from growing stage oocytes of adult ovaries were transferred to enucleated,
fully grown germinal vesicle (GV) stage oocytes. After culture in vitro, the reconstructed
oocytes matured, forming the first polar body and MII plate. To supply the ability
to form pronuclei, the resultant MII plate was transferred to enucleated MII oocytes,
which were obtained by in vitro culture of cumulus-oocyte complexes. After fertilization
in vitro, 11-15% of the reconstructed oocytes developed to morulae and blastocysts.
To assess the ability to develop to term, a total of 27 late morulae and blastocysts
were transferred to 19 recipient cows. Of the three cows that subsequently became
pregnant, one recipient, who received two embryos derived from reconstructed oocytes
with a nucleus from oocytes 100 to 109 microm in diameter, continued the pregnancy
to Day 278 of gestation. This pregnancy, however, was unexpectedly a triplet pregnancy
that included a set of identical twins and resulted in the premature birth of the
calves, followed by death from lack of post-parturient treatment. These results show
that bovine oocyte genomes are capable of supporting term development before the oocytes
grow to their full size, which suggests that growing stage oocytes can be directly
used as a source of maternal genomes.