[The origin and nature of embryonic stem cells]

The inner cell mass (ICM), blastomeres, epiblasts and primordial germ cells (PGCs) are usually used as primary materials for the establishment of embryonic stem cell (ESC) lines. ES-like cells have even been isolated from neonatal mouse testis. ESC are traditionally regarded as ICM cells, though some scholars believe they more closely resemble cells from the epiblast. However, recent evidence of ESC molecular markers indicate that the characteristics of ESC resemble those of early germ cells. The unknown origin and nature of ESC may limit the successful establishment of ESC lines from many different species. Here we review the progress of research regarding embryonic pluripotent cells, early germ cells and ESC. We find ESC can be derived from many cell types. Future study should elucidate the origin of ESC by comparing different ESC lines so as to determine the nature of ESC and improve the efficiency of ESC derivation.