Developmental potency of mouse primitive ectoderm cells, embryonic ectoderm cells and primordial germ cells after blastocyst injection

Developmental potency of primitive and embryonic ectoderm cells from 4.50-day to 6.25-day post-coitum (p.c.) mouse embryos and primordial germ cells from 12.50-day p.c. male genital ridges of fetal mice were studied by direct introducing them into 3.50-day p.c. blastocysts. Sixteen (61.5%) overt chimaeras out of 26(50% ) offsprings were obtained after transfer of 52 blastocysts injected with 4.50-day primitive ectoderm cells; four (16.0% ) overt chimaeras were obtained out of 25 (51.0% ) offsprings with 4.75-day primitive ectoderm cells from 49 transferred blastocysts. However, no overt chimaera was obtained with either 5.25-day or 6.25-day embryonic ectoderm cells or 12.50-day male primordial germ cells. GPI analysis of mid-gestation conceptuses developed from injected blastocysts showed that 5.25-day embryonic ectoderm cells could only contributed to yolk sac of con-ceptus. Results suggested that implantation acts as a trigger for the determination of primitive ectoderm cells, and their developmental potency becomes limited within a short period of time in normal development.