The ability to recapitulate the entire process of egg cell formation in a dish could have important implications in the fields of reproductive biology and regenerative medicine. Despite recent success in the production of functional sperm cells in vitro, similar methods for the creation of egg cells have been lacking.

Researchers developed a culture system that supports the fundamental events in egg cell production, including meiosis and egg cell growth. The authors analyzed patterns of gene expression in mouse ovaries that were cultured using a previously described method.

The analysis revealed that elevated estrogen signaling levels, most likely caused by fetal bovine serum (FBS) in the culture medium, were responsible for abnormalities in egg cell formation.

When the authors replaced FBS with a serum protein substitute, or added a compound that blocks estrogen receptors, the egg cells developed normally. Approximately half of the resulting egg cells were normally fertilized, and transplantation of the fertilized egg cells into female mice resulted in the birth of healthy, fertile pups.

According to the authors, the approach could be used to elucidate the mechanisms that regulate various stages of egg cell production, including the early stage of meiosis.

http://www.pnas.org/content/113/32/9021