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Tomohiro Kono1 *, Siqin Bao1
Department of Animal Science, Tokyo University of Agriculture, Setagaya-ku, Tokyo, Japan 1
It is not known when during oocyte growth the maternal genome become competent of supporting development to term. To address this question and therefore establish when mouse oocyte genome acquires ability to support full term development, we constructed oocytes using nuclei from growing oocytes (B6CBF1 mice) and assessed the ability to develop to term after fertilization in vitro. Nuclei from growing stage oocytes were transferred to enucleated fully-grown GV stage oocytes obtained from the adult females and matured in vitro. The resultant MII plate was again transferred to enucleated, freshly ovulated oocytes. The constructed oocytes were fertilized in vitro to assess the competence of genomes of the growing stage oocyte to support the development to term. The proportion of fertilized oocytes (87-97%) was similar to controls. Of the diploid monospermic embryos, 64-81% developed to blastocysts after in vitro culture for 4 days. Laparotomic observation at 9.5-18.5 days of gestation showed that more than 50 % of embryos transferred were able to implant. The first somite stage fetuses were recovered after the transfer of embryos containing maternal chromatin derived from oocytes recovered from 13-day old mice. Live fetuses were recovered on day 16.5 of gestation after the transfer of embryos containing maternal chromatin from oocytes from 15-day old. Full term development was first obtained from constructed embryos containing genomes from oocytes recovered from 16-day old mice. These results revealed that oocytes competent to develop to term appear around in 15- to 16-day old mice when the oocytes grow up to 65-70 Ám in diameter, and suggest that epigenetic modifications necessary for development are complete at this stage.
This abstract is being presented on Tuesday, August 3 at 3:45 PM at Todd 133.