For infertile couples hoping to have a baby, in vitro fertilization (IVF) is their only hope for a child, but embryos obtained from test tubes often have defects. Now, a team of scientists from the University of Montreal Hospital Research Centre has uncovered an important factor in understanding how these defects occur in developing embryos.
"About half of embryos used in fertility treatments have some cells that contain the wrong number of chromosomes. These so-called 'mosaic' embryos are considered of poor quality, and many clinics choose not to transfer them to the woman. By studying embryos in mice, we found a mechanism by which defective cells divide and perpetuate in the developing embryo," Greg FitzHarris, who participated in the research, said in a press release.
Cells with an abnormal amount of chromosomes are known to cause problems in reproduction and are typically associated with infertility, although the mechanism behind this biological event has eluded scientists until the current study.
"Using cutting edge microscopy, we are able discern small satellite-like structures called micronuclei next to the main nucleus," FitzHarris said. "By monitoring how these micronuclei-containing cells divide, we observed that the genetic material from the micronuclei was inherited by only one of the daughter cells. This suggests that micronuclei cause aneuploidy, which in turn causes mosaic embryos."
Although the study only demonstrated this process in mice, it is likely that the same mechanism is responsible for abnormal chromosome numbers in humans as well.
"This discovery is important because if future research shows that the phenomenon is the same in humans, it could provide early non-invasive detection of aneuploidy," said Jacques Kadoch, who participated in the study.
Many people argue that embryos with abnormal chromosome numbers can still produce healthy children. Whether this is true or not, a better understanding of the mechanisms that underlie embryo development is essential in order to better understand the causes of defects.
"We want to understand how to help embryos to develop normally, since ultimately we want to improve the chances of success for infertile couples who rely on medically assisted reproduction methods," FitzHarris said.
The findings were published in the Nov. 17 issue of the Proceedings of the National Academy of Sciences.
