Peptide-like substances in sheep amniotic fluid which regulate proliferation of BP-A31 cells

Cell proliferation and differentiation of developing fetus is influenced by hormones as well as insulin-like growth factors and their binding proteins contained in amniotic fluid. Our purpose was to study the actual mitogenic activity of proteins and peptides present in the sheep amniotic fluid. The cell cycle regulatory activity was estimated by using mouse fibroblasts BP-A31 as target cells. The whole amniotic fluid was inactive. However, after removal of small molecules on Sephadex G-10, the fraction eluted in the void volume (M(r) > or = 0.7 kDa) was able to induce the cell division cycle in a significant proportion of quiescent fibroblasts (Fig. 1, fraction A; Fig. 2). By further gel chromatography of this active fraction at acidic condition on Sephadex G-50, two components with mitogenic activity were separated. One component was eluted immediately after the void volume of the column, the other one was coeluted with 125I-IGF-I (Fig. 3). The functional characteristics of mitogenic signal of both components (sensitivity to mitogenic effectors) were similar to those of IGF-I and insulin (Fig. 4). We suppose that a component with higher molecular weight eluted in the vicinity of the void volume of Sephadex G-50 represents probably IGFBPs or other similar proteins.