Building an Ovary: Insights into Establishment of Somatic Cell Lineages in the Mouse

The molecular pathways that drive the differentiation of somatic cell populations in the testis and ovary have been the subjects of intensive research over the past decade. It is now clear that ovarian differentiation is a coordinate event driven by secreted factors including R-spondin1, WNT4, and follistatin and transcriptional regulators such as β-catenin and FOXL2. These factors direct bipotential somatic cell lineages toward an ovarian fate and simultaneously suppress the emergence of testis-determining processes. This review summarizes the molecular pathways responsible for establishment of the ovary and discusses the current hypotheses on the origin(s) of somatic cell lineages and how these somatic cells acquire the characteristics necessary for their function during ovarian development and maintenance.