THE IMMUNOLOCALIZATION OF BASIC FIBROBLAST GROWTH-FACTOR IN THE MOUSEUTERUS DURING THE INITIAL-STAGES OF EMBRYO IMPLANTATION

Mammalian embryo implantation involves a series of complex interaction s between maternal and embryonic cells. Uterine polypeptide growth fac tors may play critical roles in these cell interactions. Basic fibrobl ast growth factor (basic FGF) is a member of a family of growth factor s. This growth factor may be potentially important for the process of embryo implantation because it (a) is stored within the extracellular matrix and is thus easily available during embryo invasion, (b) is a p otent modulator of cell proliferation and differentiation and (c) stim ulates angiogenesis. The immunolocalization of basic FGF in the uterus during the peri-implantation period of pregnancy is presented in this study. Uterine tissue samples were obtained on days 6-9 of pregnancy with day 1 of pregnancy being the day of a vaginal copulatory plug. Ut erine samples were fixed in Bouin's fluid for no longer than 18 h. Fol lowing fixation and paraffin embedding, sections were exposed to prima ry antisera made in rabbits against either (a) human recombinant basic FGF or (b) 1-24 synthetic fragment of bovine basic FGF. The primary a ntibody was followed by biotinylated goat anti-rabbit IgG and a biotin -avidin-peroxidase complex. There were no differences in the immunoloc alization of basic FGF using either source of primary antibody. Our re sults demonstrated both temporal and spatial changes in the localizati on of immunoreactive basic FGF within the implantation chamber during days 6-9 of pregnancy. Inter-implantation sites resembled the non-preg nant uterus with basic FGF present in extracellular matrices including basal laminae. On day 6 of pregnancy, decidual cells within the prima ry decidual zone lacked both intracellular and pericellular basic FGF while non-decidualized uterine stroma resembled inter-implantation sit es. By days 7-8 of pregnancy, the secondary decidual zone had formed a nd was characterized by the distinct pericellular localization of basi c FGF around individual decidual cells. By day 9 of pregnancy, the mes ometrial region was forming and contained cords of decidual cells and a labyrinth of maternal blood vessels. The decidual cells contained di ffuse intracellular basic FGF. Trophoblast cells were devoid of basic FGF at all times examined. These results indicate that basic FGF is pr esent within the implantation chamber on days 6-9 of pregnancy and may be involved in the decidual cell response, trophoblast cell invasion and angiogenesis.