Figure 1.

Pluripotency assayed by teratoma formation. Proliferating cultures of human embryonic stem cells were used to form teratomas by renal capsule grafting by using established methods [5]. (a) An explanted teratoma is shown. (b-f) Teratomas were sectioned and stained with hematoxylin and eosin to identify embryonic tissues. Representative tissues from all three embryonic germ layers - endoderm (b), mesoderm (c, d), and ectoderm (e, f) - can be seen. (b) Glandular intestinal structure. (c) Nascent renal tubules and glomeruli within bed of primitive renal epithelium. (d) Cartilage surrounded by capsule of condensed mesenchyme. (e) Nascent neural tube. (f) Primitive squamous epithelium. Bar, 100 μm.