Human embryo in an eight-cell stage, three days after fertilization

Blastocyte with no pellucid area

Human embryo stem-cell colonies

Human embryo stem-cell colonies

SSEA4 antigen present in an undifferentiated human embryo stem-cell colony

Octamer4 (Oct4) transcription factor present in an undifferentiated human embryo stem-cell colony

α-fetoprotein present after the spontaneous differentiation of human embryo stem cells

α-fetoprotein present after the spontaneous differentiation of human embryo stem cells

α-fetoprotein present after the spontaneous differentiation of human embryo stem cells

β-tubulin present after the induced differentiation of human embryo stem cells

β-tubulin present after the induced differentiation of human embryo stem cells

α-actinin present after the induced differentiation of human embryo stem cells

α-actinin present after the induced differentiation of human embryo stem cells