Stem Cells and Development

What are stem cells?

One of the most important questions in biology is how all of the specialized, differentiated cell types in the body are formed from just a single cell. Biologists say that such a cell is totipotent (toh TIP uh tunt), literally able to do everything, to develop into any type of cell in the body (including the cells that make up the extraembryonic membranes and placenta). Only the fertilized egg and the cells produced by the first few cell divisions of embryonic development are truly totipotent. If there is a “secret” by which cells start the process of differentiation, these are the cells that know that secret.

Human Development After about four days of development, a human embryo forms into a blastocyst, a hollow ball of cells with a cluster of cells inside known as the inner cell mass. Even at this early stage, the cells of the blastocyst have begun to specialize. The outer cells form tissues that attach the embryo to its mother, while the inner cell mass becomes the embryo itself. The cells of the inner cell mass are said to be pluripotent (plu RIP uh tunt). Cells that are pluripotent can develop into most, but not all, of the body's cell types. They cannot form the tissues surrounding the embryo.

In Your Notebook Look up the roots that form the words totipotent, pluripotent, and multipotent. How do the roots relate to each cell's ability to differentiate?