Promotion of gastrulation by maternal growth factor in cultured rabbit blastocysts

Rabbit blastocysts of day 6 post coitum were cultured in a chemically defined, protein-free medium for 24 h. Although the trophoblast continued to grow, the embryonic disc degenerated. Addition of basic fibroblast growth factor (FGF-2, of human recombinant or bovine origin, 10 ng/ml) to the culture medium resulted in significant developmental progress. The embryonic disc became pear-shaped showing a round anterior edge and a posterior node. The primitive streak and Hensen's node indicated that gastrulation had begun. Mesoderm formation was confirmed from histological sections and by localization of the expression of T-gene transcripts in whole-mount preparations. FGF-2 mRNA was detected in both day-6 endometrium and day 6-blastocysts using in vitro translation followed by immunoprecipitation with a monoclonal antibody to FGF-2. In the uterine secretions of day-6 pregnant and pseudopregnant animals, several proteins exhibiting FGF-2 antigenicity were detected on Western blots following two-dimensional gel electrophoresis. As day-6 blastocysts required exogenous FGF-2 in vitro and as FGF-2 of uterine origin is present in the uterine secretion, the maternal growth factor can promote gastrulation in vivo.