LINEAGE TRACING DEMONSTRATES THAT BLASTOMERES OF EARLY CLEAVAGE-STAGEHUMAN PREEMBRYOS CONTRIBUTE TO BOTH TROPHECTODERM AND INNER CELL MASS

We injected a fluorescent lineage tracer (Texas Red-lysine-dextran) in to individual blastomeres of donated human diploid 2- to 8-cell pre-em bryos and cultured them to blastocysts. Once pre-embryos reached the e xpanded blastocyst stage, they were fixed and examined in a scanning c onfocal microscope to identify the location of fluorescent tracer. In successfully injected pre-embryos that developed to expanded blastocys ts, we found that randomly injected blastomeres formed both trophectod erm (TE) and inner cell mass (ICM). More labelled progeny were found i n TE than in ICM. Our results show that individual early blastomeres a re not yet committed to form either TE or ICM but instead can form bot h rudiments.