PROTEIN SYNTHETIC REQUIREMENTS FOR THE OUTGROWTH OF TROPHOBLAST CELLS FROM MOUSE BLASTOCYSTS

Mouse blastocysts cultured under optimal conditions attach to the surface of the culture dish and subsequently give rise to outgrowths of trophoblast cells. Migration of trophoblast cells appears to be analogous to their behavior during the invasive phase of implantation in utero. To determine the time of synthesis and nature of the products required for trophoblast outgrowth, 4th-day blastocysts were cultured in 2 different media: cNCTC, a nutrient medium supplemented with fetal calf serum, and PCMF, a simple preimplantation medium lacking amino acids and serum. Trophoblast outgrowth occurs in the former, but not in the latter, medium. Most blastocysts will give rise to outgrowths following as little as 12 h of exposure to cNCTC at the appropriate time, even if they are subsequently placed in PCMF. Outgrowth fails to occur if blastocysts are treated with cycloheximide during the interval of exposure to cNCTC; treatment with the antimetabolite after the period of culture in cNCTC does not block outgrowth. Apparently, protein(s) essential for trophoblast outgrowth are synthesized many hours prior to the actual event.