When embryos are used to generate human ESC lines, they come from donations after in vitro fertilization cycles by individuals who have given written informed written consent. Alternatively, hESC lines can be derived from donated eggs that are activated to begin development without fertilization by sperm, or from SCNT embryos.
Embryonic stem cells are usually derived from the inner cell mass of preimplantation embryos, corresponding to 5-9 days after fertilization in humans and 3-4 days in mice. Embryos used to generate human ESCs come from several sources. The first human ESCs were derived from donated embryos left after in vitro fertilization (IVF). IVF embryos analyzed by preimplantation genetic diagnosis can also be used to generate ESCs. An alteration of this technique allows generation of ESCs from single cells removed from embryos in a process similar to preimplantation genetic testing.
Embryonic stem cells (ESCs) are derived from the embryo and have the potential to become all the different cell types of the body (pluripotency). Somatic stem cells, sometimes called adult stem cells, are found in organs or tissues, can self-renew and yield the differentiated cell types comprising that organ or tissue (multipotency), and are important for maintenance and repair of the organ or tissue. Cord blood stem cells can be isolated from the umbilical cord of newborn infants and are less mature than adult stem cells. Cord blood stem cells are a type of somatic stem cell.
Totipotent cells can form all the cell types in a body, plus the extraembryonic, or placental, cells. Embryonic cells within the first couple of cell divisions after fertilization are the only cells that are totipotent. Pluripotent cells can give rise to all of the cell types that make up the body; embryonic stem cells are considered pluripotent. Multipotent cells can develop into more than one cell type, but are more limited than pluripotent cells; adult stem cells and cord blood stem cells are considered multipotent.
No. Stem cells isolated from different sources and tissues are distinct in that they have varying degrees of potency (see next question) and give rise to differing mature cell types. Additionally, as each person differs slightly at the genetic level (their DNA sequence), the stem cells derived from each individual are likewise different.
Stem cells have the remarkable potential to develop into many different cell types in the body. They can divide without limit to replenish other cells, serving as a sort of repair system for the body. When a stem cell divides, each new cell has the potential to either remain a stem cell or become another type of cell with a more specialized function, such as a muscle cell, a red blood cell, or a brain cell. ∗
Cells are the structural and functional units of all living organisms. Some organisms, such as bacteria, are unicellular, consisting of a single cell. Other organisms are multicellular and may have many cells. Humans have an estimated 100,000,000,000,000 (one hundred trillion) cells and more than 200 different types of cells (liver cells, skin cells, muscle cells, etc.). ∗
