Mutants for either bone morphogenetic protein 15 (BMP15) or growth differentiation factor 9 (GDF9), have ovaries with a significant proportion of MOFs.39 Both BMP15 and GDF9 are secreted by the oocyte early in ovarian differentiation, supporting the notion that signals from the oocyte to the granulosa cells are important for cyst breakdown and follicle formation. This evidence concerns the gene BMP15 and cyst.