Initiation of Conceptus Elongation Coincides with an Endometrium Basic Fibroblast Growth Factor (FGF2) Protein Increase in Heifers

Abstract

Fibroblast growth factors (FGF) play an important role during embryo development. To date, the role of FGF and the respective receptors (FGFR) during the preimplantation phase in cattle are not fully characterized. We examined FGF1, FGF2, FGFR1, FGFR2, and FGFR3 in cyclic and early pregnant heifers at Days 12, 15, and 18 after insemination (Day 0). Endometrial FGF1 mRNA transcript abundance in heifers varied significantly with respect to the day after insemination, the pregnancy status, and their interaction. The expression was higher in nonpregnant than in pregnant heifers at Day 18. The conceptus transcripts abundance of FGFR2 and FGFR3 were significantly lower at Day 15 than 18. In the endometrium, FGF1 protein abundance significantly decreased from Day 12 onwards and FGF2 protein abundance showed a minor, but a significant increase at Day 15 in comparison to Days 12 and 18. We concluded that the decrease in FGF1 mRNA expression in pregnant heifers at Day 18 points towards a potential contribution of FGF1 in the preimplantation process. Additionally, successful embryo elongation might require a spatiotemporal FGF2 protein increase in the endometrium.

Keywords: FGF2; angiogenesis; bovine; embryo; interferon-tau.

Figure 1

The mRNA was expressed in the endometrium of nonpregnant (n = 5 to 8) and pregnant (n = 5 to 6) Simmental heifers at Days 12, 15, and 18 post insemination as well as conceptus at Days 15 (n = 4 to 8) and 18 (n = 4) (insemination = Day 0). (A) mRNA expression of fibroblast growth factor 1 (FGF1) and the mRNA transcripts’ abundance was below the detection limit on Days 15 and 18 in the conceptuses; (B) FGF2 mRNA expression; (C–E) mRNA expression of FGF receptors 1 (FGFR1), FGFR2, and FGFR3 (IIIc isoforms). An asterisk (*) indicates significant differences between groups and different letters within nonpregnant (a,b) and pregnant (x,y) heifers indicate significant differences within groups over time (days) (A,B) and between days (D). Abbreviation P4 = progesterone and E2 = estradiol-17β. The results presented as mean delta quantitative cycle (ΔCq) ± standard error of the mean, and high ΔCq represent a high transcript abundance. Differences were considered significant at a 95% confidence interval.

Figure 2

(A) Immunohistochemical localization of fibroblast growth factor 1 (FGF1) protein (brown), (B) the localization of FGF2 protein, and (C) the negative control. Positive staining for FGF1 and FGF2 in the endometrium of Simmental heifers was observed in luminal (a) and glandular (b) epithelium, in the stromal endometrium (c) and in blood vessels (d).

Figure 2

(A) Immunohistochemical localization of fibroblast growth factor 1 (FGF1) protein (brown), (B) the localization of FGF2 protein, and (C) the negative control. Positive staining for FGF1 and FGF2 in the endometrium of Simmental heifers was observed in luminal (a) and glandular (b) epithelium, in the stromal endometrium (c) and in blood vessels (d).

Figure 3

Fibroblast growth factor (FGF) protein abundance in the endometrium of nonpregnant (n = 6 to 8) and pregnant (n = 5 to 6) Simental heifers after insemination (insemination = Day 0). (A) FGF1 protein abundance; (B) FGF2 protein abundance. Days with a common letter (a,b) were not significantly different. Differences were considered statistically significant at a 95% confidence interval.