117 FIBROBLAST GROWTH FACTOR RECEPTOR-1c, -2c, -3c, and -4 mRNA ABUNDANCE IN GRANULOSA CELLS DURING FOLLICULAR GROWTH IN CATTLE

Abstract

Fibroblast growth factors (FGF) regulate folliculogenesis of several species, including cattle. The cellular responses to a particular FGF are influenced by the diversity of high affinity fibroblast growth factor receptors (FGFR). There are 4 distinct genes encoding FGFR in vertebrates and the occurrence of mRNA splicing in the immunoglobulin-like domain III generates a diversity of sequences, and results in various isoforms of FGFR1, FGFR2, and FGFR3 (but not of FGFR4). Because FGFR have different ligand specificities, the presence of FGFR in bovine antral follicles is of fundamental importance for the FGF to exert their effects in the ovary. Hence, the objective of this study was to determine if FGFR1c, FGFR2c, FGFR3c, and FGFR4 mRNA abundance in granulosa cells (GC) change according to follicular size, steroidogenic status, and days post-ovulation during growth of first-wave dominant follicles in cattle. Oestrous cycles of non-lactating dairy cattle were synchronized and ovaries were collected on either Day 3–4 (n = 8) or Day 5–6 (n = 8) post-ovulation (as assessed by rectal ultrasonography). Follicular fluid (FFL) was aspirated from small (1–5 mm), medium (5.1–8 mm), or large (8.1–18 mm) follicles for measurement of oestradiol (E2) and progesterone (P4) levels by radioimmunoassay, and GC were collected for mRNA extraction. Relative quantity of target gene mRNA was expressed as 2^−ΔΔCt using the comparative threshold cycle (Ct) method. Data were transformed to natural log (x + 1), to correct for heterogeneity of variance, and analysed via factorial ANOVA with the general linear model procedure of SAS and are reported as least squares means ± s.e.M. Follicle group (based on steroidogenic status and size of follicles), but not days post-ovulation or their interaction, significantly affected FGFR1c, FGFR2c, and FGFR3c mRNA abundance, whereas FGFR4 mRNA abundance was not affected by follicle group or days post-ovulation. FGFR1c mRNA abundance was greater (P < 0.01) in large (44.8 ± 11.3; n = 29), medium (63.8 ± 7.6; n = 64), and small (44.6 ± 11.2; n = 29) E2-inactive (FFL E2/P4 ratio < 1) than in large E2-active (FFL E2/P4 ratio > 1) follicles (10.5 ± 15.5; n = 16) and greater (P < 0.05) in medium E2-inactive than in large and small E2-inactive follicles. FGFR2c mRNA abundance was greater (P < 0.01) in large (423.9 ± 131.9), medium (585.8 ± 97.0), and small (273.6 ± 143.2) E2-inactive than in large E2-active (56.2 ± 195.6) follicles. The FGFR3c mRNA abundance was greater (P < 0.05) in large (143.4 ± 40.2) and medium (160.2 ± 29.3) E2-inactive than in large E2-active (43.2 ± 58.6) follicles and tended to be greater (P = 0.06) in small E2-inactive (101.9 ± 42.9) than in large E2-active follicles. Taken together, the findings that FGFR1c, FGFR2c, and FGFR3c mRNA abundance is lower in GC of E2-active follicles during growth of the first dominant follicle support an anti-differentiation role for these FGFR as well as support the idea that some FGF may regulate the selection of dominant follicles in cattle.