Practice question

Induced pluripotent stem cells are engineered by ectopic expression of pluripotency transcription factors in fibroblasts or other somatic cells, erasing somatic epigenetic memory and restoring embryonic-like state. Because they arise exclusively through artificial reprogramming, they are absent from normal embryogenesis and not present in blastocyst or fetus. Naturally occurring pluripotent cells include inner cell mass and epiblast-derived embryonic stem cells. iPSCs share hallmarks of indefinite self-renewal and capacity to form all three germ layers, providing patient-specific models for disease, drug screening, and regenerative approaches without embryo use.