What Are Stem Cells?

All stem cells have the ability to divide and renew indefinitely into millions of cells, are unspecialized cells, and can differentiate into at least several kinds of cells. The self-renewing and division of these cells is known as proliferation. There are two major types of stem cells, embryonic stem cells that are derived from embryos during the earliest stages of human development, and adult stem cells which exist in small quantities in each of our bodies. Adult stem cells, also known as somatic stem cells, remain in a quiescent (non-dividing) state until they are needed to regenerate and repair other cells that have suffered damage. These are the cells that are at work in healing your skin when you get a cut.

Human embryonic stem cells (hES) are the focus of the stem cell debate; these cells contain different levels of potentiality in becoming full-grown persons at different stages. These cells are made by taking a fertilized egg and placing it on a feeder tray for four to six days. Up until the sixteen-cell stage, each cell is totipotent or "totally potent." This means that each of these cells has the potential to become a human being. If totipotent cells have access to a placenta they can continue developing into a child. Once past the sixteen-cell stage, cells become pluripotent. Pluripotent cells are limited to differentiating into three major tissue types:

1. Endoderm - interior gut lining

2. Mesoderm - muscle, blood, bone

3. Ectoderm - epidermal & nervous system

Pluripotent cells can no longer become human beings and do not constitute an embryo. These are the cells used embryonic stem cell research.

Adult stem cells are multipotent and begin forming when the fetus is eight months old. These cells do have potential to develop into several different kinds of cells, but they do have limitations which the pluripotent cells do not have. Human embryonic germ cells (hEG) which are taken from an aborted fetus before the gender has been determined, are another source of stem cells for research.¹

Research on hES cells was initiated in 1988 and these cells are an interesting area of research because they can show how an organism is developed from one cell. Scientists are asking how these cells remain undifferentiated and are able to continually renew themselves. They are also wondering, what are the signals that trigger stem cells to differentiate and become the variety of cells that make up the human body? hES cells are triggered by both internal and external mechanisms, including genes encoded in cell DNA, chemicals secreted by other cells, contact with neighboring cells, and molecules in their immediate micro-environment.² If scientists could figure out the complex combination of triggers which leads to the creation of specific cells, cell based therapies could be developed.

A biolaser was developed at Sandia National Laboratories in New Mexico which has the ability to let scientists see what is going on inside a single stem cell. They can even zoom in on mitochondria and examine it to see if it is cancerous. Sandia National Laboratories says that more time will be needed to further develop this technology, but they hope to be able to use it to gain insight into the triggers used in cell differentiation.³

Sources:

1) Peters, Ted. Science, Theology & Ethics. Ashgate Publishing Company. Burlington. 2003. pp. 177-185

2) National Institute of Health. "Stem Cell Basics." http://stemcells.nih.gov/info/basics/basics6.asp

3) Philipkoski, Kristin. "Biolaser lights up stem cells." Wired News. Mar 31 2005.