Table 3.

Factors that can promote growth and development of preantral follicles [2, 3].

Factor	Origin	Function
TNFα	Oocyte	Regulates apoptosis of oocytes
BMP15	Oocyte	Differentiation and proliferation of primary follicles
GDF 9	Oocyte	Differentiation and proliferation of primary follicles
EGF/bFGF	Oocyte	Induces development of primordial and preantral follicles
Figα (Figla)	Oocyte	Coordination of structural genes for development of the primordial follicle such as Zp1, Zp2, and Zp3 of the ZP
Protein ckit	Oocyte and theca	Transition of primordial follicle to primary follicle. Migration and proliferation of germ cells
Activin	Granulosa cells	Proliferation of granulosa cells
KL	Pregranulosa cells	Induces development of primordial follicle to primary follicle
GH	Endocrine	Development of GC and theca cells of preantral follicles
Insulin	Endocrine	Induces development of the primordial follicle to primary follicle
IGF-I	Granulosa cells	Stimulates development from preantral follicle to antral follicle
AMH	Granulosa cells	Inhibition of primordial follicle development
AhR	Granulosa cells	Regulation of the oocyte pool size
BMP4	Theca/stroma	Promotes transition from primordial follicle to primary follicle and oocyte survival
KGF	Theca	Proliferation of granulosa cells

AhR: Aromatic hydrocarbon receptor, AMH: anti-Mullerian hormone, BMP: bone morphogenic protein, EGF/bFGF: epidermis growth factor/basic fibroblast growth factor, GDF: growth differentiation factor, GH: growth hormone, Figα: factor in the germline alpha, IGF: insulin growth factor, KGF: keratinocyte growth factor, KL: Kit ligand, TNF: tumor necrosis factor.