Genetic clues contained in the cells that nurse and nurture developing eggs could help identify which ones to choose for IVF.
There is currently little that can be done to predict which eggs are most likely to generate healthy embryos. After an egg has been fertilized, doctors can take biopsies from early embryos or examine their shape to predict which are most likely to implant and produce healthy children. Despite this, around 8 out of 10 embryos conceived through IVF fail to implant when transferred to the womb.
While an egg is developing it is nurtured by specialized cells called cumulus cells, which provide it with the nutrients it needs to grow. "The final state of the egg depends on the relationship with the cumulus cells," says Samir Hamamah at the Montpellier University Hospital in France. So he and his colleagues wondered whether there are genetic markers in these cells that could predict the quality of the resulting embryos and the likelihood of a successful pregnancy.
To investigate further, the team retrieved eggs and their associated cumulus cells from 30 women undergoing IVF. After extracting and freezing the cumulus cells, they fertilized the eggs by intra-cytoplasmic sperm injection (ICSI) and inspected the resulting embryos for quality. They then looked at the gene expression profiles of the cumulus cells corresponding to the eggs that produced good and bad embryos, as well as those that failed to fertilize.
This analysis showed that the levels of expression of three genes, called BCL2L11, PCK1 and NFIB, were strongly associated with embryo quality (Molecular Human Reproduction, DOI: 10.1093/molehr/gan067). BCL2L11 is involved in triggering cell death in response to abnormalities, PCK1 is associated with energy production, and NFIB regulates some of the earliest processes in embryo development.
Hamamah's finding opens up the possibility that doctors might be able to check the level of expression of these cumulus cell genes to predict the viability of the egg. "This is a novel concept, offering a new potential strategy for competent embryo selection," he told a meeting of the Preimplantation Genetics Diagnosis International Society in Miami, Florida, last week.Fertility doctors might be able to check the level of gene expression to predict the viability of an egg
He plans to confirm that this strategy works by using the three genetic markers to select eggs to fertilize and implant, and then see how many of these result in healthy pregnancies compared with those from unscreened eggs.
"Trying to establish the importance of particular gene products in assessing embryo viability is very important," says Simon Fishel, managing director of the Care fertility clinic in Sheffield, UK. "Whether it will become a valuable clinical [tool] remains to be seen. Our understanding of genes in relation to embryo viability is still crude."
