Detecting a bad egg

The inability to predetermine an oocytes' potential to produce a competent embryo is a major obstacle facing both human and animal assisted reproduction technologies. The identi. cation of biological markers indicative of increased or decreased oocyte (egg) quality would allow for the selection of high quality oocytes, resulting in the transfer of fewer embryos per cycle and increased pregnancy rates. The ability of an embryo to develop successfully greatly relies on the quality of the oocyte from which it has been generated. Oocyte competence is acquired during an oocyte's growth and maturation. An unfavourable maturation environment can lead to diminished oocyte quality and have a detrimental impact on subsequent embryonic development. In extreme cases, irreparably damaged oocytes undergo apoptosis. For example, this is a damaged bovine oocyte that was matured in vitro in the presence of Trilostane, a chemical that prevents progesterone synthesis. Staining for chromatin (blue) shows the formation of a metaphase (MII) plate within the oocyte, indicating that the oocyte has completed the maturation process. The accumulation of active caspase-3 (yellow ), an end marker of apoptosis, in this oocyte is indicative of its low quality and the limited potential to be fertilized or to undergo embryonic development.