Abstract: 562

MIXOPLOIDY IS FREQUENT AT DAY 2 - 5 IN BOVINE EMBRYOS PRODUCED IN VITRO.

D Viuff^{1 *}, B Avery¹ , P Hyttel² , T Greve^{1 *}, PD Thomsen²
Department of Clinical Studies, Reproduction, Royal Veterinary and Agricultural University, Frederiksberg C, Denmark ¹
Department of Anatomy and Physiology, Royal Veterinary and Agricultural University, Frederiksberg C, Denmark ²

We have previously detected chromosome abnormalities using multicolour fluorescence in situ hybridization (FISH) in in vitro produced bovine blastocysts revealing a mixoploidy rate at 72%. This study was undertaken to determine systematically the incidence of chromosomal abnormalities in earlier developmental stages in order to study the chronological background for establishment of mixoploidy.We collected in vitro produced bovine embryos at day 2, 3, 4 and 5 post insemination (pi) and analysed isolated nuclei by multicolour FISH using a chromosome 6- and a chromosome 7-specific DNA probe. At Day 2 pi, chromosomal abnormalities were found in 33% of 2-cell embryos (N=12), in 30% of 3-4-cell embryos (N=39) and in 14% of 5-8-cell embryos (N=29). At Day 3 pi, chromosomal abnormalities were detected in 57% of 3-4-cell embryos (N=14), in 17% of 5-8-cell embryos (N=52) and in none of the 9-12-cell embryos (N=2). At Day 4 pi, chromosomal abnormalities were found in none of 3-4-cell embryos (N=2), in 24% of 5-8-cell embryos (N=17), 19% of the 9-16-cell embryos (N=21) and in none of the 17-25-cell embryos (N=11). At day 5 pi, chromosomal abnormalities were detected in 50% of the 5-8-cell embryos (N=4), in 31% of the 9-16-cell embryos (N=16), in 55% of the 17-25-cell embryos (N=11), in 57% of the 26-35-cell embryos (N=7) and in 60% of the embryos that contained more than 36 cells (N=5). In conclusion, numerical chromosome abnormalities are frequent already at Day 2 pi. The most frequent chromosome abnormality from day 2-5 pi was mixoploidy (23%), whereas aneuploidy, i.e. all nuclei in the embryo showed chromosome abnormality, was only detected in 4% of the embryos. Moreover, slowly developing embryos appear to have a higher incidence of abnormalities.

    This abstract is being presented on Tuesday, August 3 at 4:30 PM at Todd 133.