Stage-specific Embryonic Antigens
SSEAs were originally identified by monoclonal antibodies recognizing defined carbohydrate epitopes associated with lacto- and globo-series glycolipids. They are often used as markers for stem cell differentiation. CD15/Lewis X/SSEA-1 is expressed on murine embryonal carcinoma (EC) cells, embryonic stem (ES) cells, and primordial germ cells. SSEA-3 and SSEA-4 are synthesized during oogenesis and is present on oocyte, zygote, and early cleavage-stage embryo membranes. Mouse CD15/Lewis X/SSEA-1 expression decreases with differentiation as SSEA-3 and SSEA-4 expression increase. In contrast, human EC and ES cells express SSEA-3 and SSEA-4, and differentiation is accompanied by an upregulation of CD15/Lewis X/SSEA-1 and down-regulation of SSEA-3 and SSEA-4.