230 EXPRESSION OF mRNA ENCODING FGF10 AND COGNATE RECEPTORS (FGFR1B AND FGFR2B) AROUND FOLLICLE DEVIATION IN NELORE HEIFERS

Abstract

A member of the FGF7 subfamily, FGF10 acts via FGFR2B and FGFR1B. In bovine antral follicles, FGF-10 was detected in oocytes and theca cells (TC). Levels of mRNA were negatively correlated with intrafollicular concentrations of estradiol, and FGF10 inhibited estradiol production from granulosa cells (GC). In Nellore (Bos indicus), morphological divergence occurs on average 2.5 days after ovulation, when dominant follicle diameter is around 6.0 mm. To gain insight into the involvement of the FGF10 system in the control of follicle selection, we assessed mRNA expression of FGF10 in TC and of FGFR1B and FGFR2B in GC from dominant and subordinate follicles around deviation in Nellore heifers. Thirteen Nellore heifers were hormonally synchronized, and ovulation was detected by ultrasound monitoring every 12 h. Heifers were slaughtered 2 (n =4), 2.5 (n = 5), and 3 (n = 4) days after ovulation. Granulosa cells and TC were separated from the 2 largest follicles and submitted to total RNA extraction. mRNA abundance of CYP19 (aromatase), FGF10, FGFR1B, and FGFR2B was measured by real-time RT-PCR and normalized by the expression of cyclophilin A (CYCA) and GAPDH, for TC and GC, respectively. Dominant and subordinate follicles were considered those expressing the greatest and second-greatest abundance of CYP19 mRNA in GC within each heifer. Effects of follicle status and day on CYP19, FGF10, FGFR2B, and FGFR1B mRNA abundance were tested by ANOVA. On Day 2, FGFR2B mRNA abundance was greater in GC of subordinate follicles compared with dominant follicles (P = 0.006), and that of FGF10 in TC tended to exhibit the same pattern (P = 0.06). Follicle diameter was not different between dominant and subordinate follicles on Day 2 (5.5 ± 0 v. 5.12 ± 0.3 cm). On Day 2.5, FGF10 expression was greater in TC from subordinate follicles (P = 0.01), and FGFR2B expression in GC was no longer different between dominant and subordinate follicles. Follicle diameter was greater in dominant follicles on Day 2.5 (6.7 ± 0.2 v. 5.8 ± 0.3 cm; P = 0.04). On Day 3, no differences were observed between dominant and subordinate follicles for any of the genes assessed. mRNA expression of FGFR1B in GC did not change with follicle status or day. In conclusion, expression of FGF10 and FGFR2B was decreased in dominant follicles around morphological divergence, suggesting their involvement in the mechanisms controlling dominant follicle selection. As FGF10 inhibits estradiol production of GC, we propose that FGF10 and FGFR2B are suppressed in the dominant follicle to allow acquisition of full steroidogenic capacity.

This research was supported by FAPESP.