Insulin is produced by the green cells that are in clusters about the same size as the islets in the human pancreas. The red cells are producing another metabolic hormone, glucagon, that prevents low blood sugar. Harvard University hide caption

itoggle caption Harvard University

Each of these mouse pups was born from an egg scientists created using embryonic stem cells. It's possible the technology could change future treatment for human infertility. Katsuhiko Hayashi hide caption

itoggle caption Katsuhiko Hayashi

Sue Freeman, 78, checks her email at her home in Laguna Beach, Calif., on Saturday. She says her eyesight improved markedly since she received an experimental stem-cell procedure last July. Melissa Forsyth for NPR hide caption

itoggle caption Melissa Forsyth for NPR