title: Investigations of TGF-β signaling in preantral follicles of female mice reveal differential roles for bone morphogenetic protein 15.
abstract: Bone morphogenetic protein 15 (BMP15) and growth differentiation factor 9 (GDF9) are 2 closely related TGF-β ligands implicated as key regulators of follicle development and fertility. Animals harboring mutations of these factors often exhibit a blockage in follicle development beyond the primary stage and therefore little is known about the role of these ligands during subsequent (preantral) stages. Preantral follicles isolated from immature mice were cultured with combinations of BMP15, GDF9, and activin receptor-like kinase (ALK) inhibitors. Individually, GDF9 and BMP15 promoted follicle growth during the first 24 hours, whereas BMP15 subsequently (48-72 h) caused follicle shrinkage and atresia with increased granulosa cell apoptosis. Inhibition of ALK6 prevented the BMP15-induced reduction in follicle size and under basal conditions promoted a rapid increase in granulosa cell proliferation, suggesting BMP15 signals through ALK6, which in turn acts to restrain follicle growth. In the presence of GDF9, BMP15 no longer promoted atresia and in fact follicle growth was increased significantly more than with either ligand alone. This cooperative effect was accompanied by differential expression of Id1-3, Smad6-7, and Has2 and was blocked by the same ALK5 inhibitor used to block GDF9 signaling. Immunostaining for SMAD2/3 and SMAD1/5/8, representing the 2 main branches of TGF-β signaling, supported the fact that both canonical pathways have the potential to be active in growing follicles, whereas primordial follicles only express SMAD2/3. Overall results highlight differential effects of the 2 main TGF-β signaling pathways during preantral follicle growth.
authors.affiliation: Institute of Reproductive and Developmental Biology, Imperial College London, Hammersmith Hospital, Du Cane Road, London W12 0NN, United Kingdom. m.a.fenwick@sheffield.ac.uk
authors.forename: Mark A
authors.initials: MA
authors.lastname: Fenwick
authors.forename: Jocelyn M
authors.initials: JM
authors.lastname: Mora
authors.forename: Yosef T
authors.initials: YT
authors.lastname: Mansour
authors.forename: Christina
authors.initials: C
authors.lastname: Baithun
authors.forename: Stephen
authors.initials: S
authors.lastname: Franks
authors.forename: Kate
authors.initials: K
authors.lastname: Hardy
mesh_terms: D030201:Activin Receptors, Type I / Q000037:antagonists & inhibitors / Q000378:metabolism; D030301:Activin Receptors, Type II; D000818:Animals; D017209:Apoptosis; D055430:Bone Morphogenetic Protein 15 / Q000235:genetics / Q000378:metabolism*; D005260:Female; D005496:Follicular Atresia; D005786:Gene Expression Regulation / Q000187:drug effects; D006107:Granulosa Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D055429:Growth Differentiation Factor 9 / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008024:Ligands; D051379:Mice; D008810:Mice, Inbred C57BL; D006080:Ovarian Follicle / Q000166:cytology / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D018125:Receptors, Transforming Growth Factor beta / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D046509:Tissue Culture Techniques; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*
chemical_list: C525901:BMP15 protein, human; D055430:Bone Morphogenetic Protein 15; C525898:Gdf9 protein, mouse; D055429:Growth Differentiation Factor 9; D008024:Ligands; D047428:Protein Kinase Inhibitors; D018125:Receptors, Transforming Growth Factor beta; D011994:Recombinant Proteins; C508961:Tgfb1 protein, mouse; D053773:Transforming Growth Factor beta1; D030201:Activin Receptors, Type I; D030301:Activin Receptors, Type II; C498931:Acvrl1 protein, mouse