Functional Genomics of the Origin of Stem Cells
The first lineage differentiation event during mammalian embryonic development occurs during blastocyst formation. Cells lying at the outside of the embryo adopt epithelial fate, while cells inside remain pluripotent. The epithelium is called trophectoderm (TE) and gives rise to the trophoblast lineage later. The inside cells are called inner cell mass (ICM) and give rise to the epiblast. Embryonic stem (ES) cells are derived from the ICM. To understand the origin of stem cells, we have used microarrays to examine the developmental changes in gene expression from the time of ovulation to the blastocyst stage, and have compared gene expression in the ICM to that in the whole blastocyst. Analysis of the data revealed genes that are induced during blastocyst formation and differentially expressed between ICM and TE. We are analyzing selected genes for their roles in lineage differentiation, development, and stem cell formation/maintenance.