Fibroblast growth factor-2 expression in the preimplantation equine conceptus and endometrium of pregnant and cyclic mares.

This study looks into the roles of uterine-derived fibroblast growth factor-2 (FGF2) in the development of the conceptus (embryo and surrounding tissues) in horses during early pregnancy and the estrous cycle. The researchers found that FGF2 and its receptors, as well as the activating factor FGF binding protein, were expressed in the equine endometrium and the embryo’s trophectoderm throughout these periods, suggesting a possible role in trophoblast development and adhesion.

Understanding the Role of FGF2

• This research investigates the expression of fibroblast growth factor-2 (FGF2) and its receptors in the endometrium and trophectoderm of mares during early pregnancy and the estrous cycle.
• FGF2 is known to promote embryogenesis, trophoblast cell migration, and adhesion in several species. Trophoblast cell migration and adhesion are crucial steps in the establishment of pregnancy.
• The study showed that FGF2 and its receptors are present in both the endometrium (the inner lining of the uterus) and the trophectoderm (the cell layer that forms contact with the endometrium and develops into the placenta) from day 14 to day 28 of the gestation period.

FGF2 Expression in Endometrium and Trophectoderm

• The researchers noted that the level of FGF2 expression in the endometrium was higher during estrus than on days 7 or 14 of diestrus, indicating estrogen dependency.
• Both the transcript and protein of FGF2 in the endometrium were noted to increase as pregnancy progressed from day 21 to day 28, with FGF2 protein predominantly localized in the luminal and glandular epithelium.
• FGF2 mRNA was detectable in trophectoderm as early as day 14, and there were increases in transcripts and translation on day 21 and 28 of pregnancy.

Expression of FGF2 Receptors and Activating Factor

• In terms of FGF2 receptors (FGFR1-4), the study found that FGFR1 mRNA was down-regulated in the endometrium at day 7 of diestrus but increased again by day 14. During early pregnancy, endometrial FGFR1 expression decreased while FGFR2IIIc expression did not change.
• The researchers observed that the expression of all FGFRs in the conceptus increased as pregnancy progressed.
• As for the expression of FGF binding protein (FGF-BP) – the activating factor of FGF2 – it remained constant in the endometrium throughout the observed period but saw an increase in the conceptus between days 14 and 28, suggesting a specific role in regulating FGF2 activity in the developing embryo.

Implications of the Study

• The findings suggest that the equine endometrial epithelium produces FGF2 during weeks 3 and 4 of pregnancy, which may contribute to trophoblast development and adhesion – a crucial step in establishing successful pregnancy.
• They also provide hints at the possible estrogen dependency of FGF2 expression and its roles at different stages of the estrous cycle and early pregnancy, which may feed into the broader understanding of the reproductive process in horses.