Expression and Localization of Fibroblast Growth Factor (FGF) Family Members during the Final Growth of Bovine Ovarian Follicles

The aim of this study was to investigate the possible participation of fibroblast growth factor (FGF) family members: FGF1, FGF2, and FGF7, and their receptor variants: FGFR, FGFR2IIIb, and FGFR2IIIc in theca interna (TI) and granulosa cell (GC) compartments of bovine follicles during final growth. A classification of follicles into five groups (<0.5; >0.5-5; >5-20; >20-180; >180 ng/ml, respectively) was performed according to the follicular fluid (FF) oestradiol-17β (E) content. The mRNA expression and protein localization was analyzed by reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry. FGF1 mRNA expression was relatively high in TI and lower in GC, and without any regulatory change for both tissue compartments during final follicular growth. The FGF1 protein could be predominantly localized in the cytoplasm of GC, in smooth muscle cells of blood vessels, in the rete ovarii, and at a lesser degree in theca cells. FGF2 mRNA in TI increased significantly in large follicles and was low and without any regulatory change in GC. FGF7 mRNA expression was relatively high in TI and very low in GC. For FGF7 in mature follicles a marked staining of the TI and the basal layers of the GC could be demonstrated. The mRNA signal for the FGFR in TI increased significantly with beginning of E production (E>0.5-5 ng/ml FF) and was without any regulatory change in GC. The mRNA expression of FGFR2IIIb was relatively high in GC and increased significantly during final growth of follicles in contrast to the TI with very low expression. The FGFR2IIIc mRNA expression in TI and GC was relatively high but without any clear change. Our results suggest that FGF growth factor family members are involved in process of folliculogenesis and especially during final growth of the preovulatory (dominant) follicle by stimulation of angiogenesis and GC survival and proliferation.