Fibroblast growth factor induces primitive streak formation in rabbit pre-implantation embryos in vitro.

Culturing of rabbit pre-implantation embryos was performed in Ham's F10 medium supplemented with polyvinylpyrrolidone. Under these culture conditions, day 6 post coitum blastocysts increased their diameter within 24 h to 80% of that of day 7 blastocysts grown in vivo. Despite this substained growth, the embryonic disc remained undifferentiated with clear signs of degeneration after 24 h of culture. Basic fibroblast growth factor (bFGF) was able to overcome this developmental block. After 12 h of culture, day 6 blastocysts showed pear-shaped embryonic discs, and after 24 h, the primitive streak with Hensen's node was visible. The bFGF had no comparable effects on day 5 and day 7 blastocysts. The embryonic discs of day 5 blastocysts degenerated, even in the presence of bFGF, whereas day 7 blastocysts were able to form their primitive streak, also in the absence of bFGF. TGF beta 1 did not promote embryonic development in vitro. The data indicate that the onset of mesoderm formation in the rabbit is controlled by a growth factor of the FGF-family.