Required for ovarian folliculogenesis. Promotes primordial follicle development. Stimulates granulosa cell proliferation. Promotes cell transition from G0/G1 to S and G2/M phases, through an increase of CCND1 and CCNE1 expression, and RB1 phosphorylation. It regulates STAR expression and cAMP-dependent progesterone release in granulosa and thecal cells. Attenuates the suppressive effects of activin A on STAR expression and progesterone production by increasing the expression of inhibin B. It suppresses FST and FSTL3 production in granulosa-lutein cells. Homodimer or heterodimer (Potential). But, in contrast to other members of this family, cannot be disulfide-linked (By similarity). Expressed in ovarian granulosa cells. Present in oocytes of primary follicles (at protein level). Phosphorylated; phosphorylation is critical for GDF9 function. In vitro, can be phosphorylated by CK at Ser-325. Altered GDF9 function may be involved in ovarian disorders and contribute to the likelihood of dizygotic twinning. The disease is caused by variants affecting the gene represented in this entry. Ovarian physiology and fertility are controlled by endocrine and paracrine signals. These act in a species-dependent manner and determine the ovulation quota in different mammalian species. While humans, and mammals such as the cow or red deer, normally ovulate only one egg per cycle, other mammals such as mouse and pig can ovulate in excess of ten per cycle. The mechanisms that regulate the species-specific differences in the number of follicles that go onto ovulate during each reproductive cycle are poorly understood. According to PubMed:21970812, mRNA expression levels of GDF9 and BMP15 are tightly coregulated within each species and influence species-specific ovulation-rates. Belongs to the TGF-beta family.