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Stem Cells

A stem cell is a cell whose job in the body is not yet determined. All other cells in the body "stem" from these type of cells (hence the name)

Stem cells wait in the body until they get a signal to DIFFERENTIATE, or gradually change into the desired cell type - this occurs when the signal "turns on" specific genes in the stem cell. This process helps cells specialize so they can do different jobs.

Stem Cells can become:

    • skin cells
    • Red blood cells
    • Nerve Cells
    • Skeletal muscle cell

What are stem cells and why are they important?

  • undifferentiated cells that renew themselves over long periods through cell division
  • under certain conditions, these cells will differentiate and become functioning body cells (such as muscle or neurons)
  • Stem cells can be found in adults, but most of the promising research comes from embryonic stem cells
  • A 3 to 5 day old embryo (called a blastocyst) has a group of 30 or more cells that will become all the cells of the body. All the cells of the body -stem- from this small group of cells
  • Scientists hope to use these cells to treat diseases

What are the unique properties of all stem cells?

Types of Stem Cells

Totipotent - cells can become ANY kind of cell in the body
Pluripotent - cells can become almost any kind of cell in the body
Multipotent - cells can differentiate only into a limited range of cell types
  • Stem cells are unspecialized - they can potentially become any type of cell
  • Stem cells are capable of dividing and renewing themselves - unlike many body cells that don't divide and renew - this long term renewal is called PROLIFERATION
  • Factoid: it took 20 years for scientists to figure out how to get mouse embryo cells to proliferate for long periods without spontaneously differentiating
  • Stem cells give rise to specialized cells - though the signals required to coax the cells into doing this is not yet understood fully

What are embryonic stem cells?

  • cells derived from embryos that are created in vitro - eggs that are fertilized outside the body. (When a woman has this procedure done for the purpose of getting pregnant, many eggs are fertilized but only some are implanted back into the woman, the rest are normally discarded)
  • the blastocyst (early embryo) is 4-5 days old
  • the cells from the blastocyst are transferred to a petri dish containing nutrients, where they grow and divide
  • when the petri dish becomes crowded, some cells are transferred to other dishes, this process is repeated many times
  • one blastocyst can yeild millions of cells
  • embryonic stem cells that have proliferated in this way for 6 months or more are called a STEM CELL LINE
  • cells from the cultures can be frozen and shipped to other laboratories for research

What are adult stem cells?

  • only certain tissues are thought to contain stem cells
  • these stem cells divide but remain inactive until triggers (like an injury) prompt them to differentiate
  • these adult stem cells will only become certain types of cells, unlike embryonic stem cells, they are limited in what they can become
  • Ex. bone marrow stem cells can become bone or cartilage or other connective tissue, but cannot become a brain cell
  • New experiments suggest that stem cells can actually become nonrelated cells (a bone marrow cell may be able to turn into a neuron, but experiments are sketchy in this area) - the ability of stem cells to become a different type of cell is called PLASTICITY
  • Adult stem cells are difficult to grow in a petri dish, making it difficult to develop large numbers of these cells (unlike embryonic stem cells)

What are the potential uses of stem cells?

  • research to determine the signals that result in differentiation
  • developing ways to manipulate genes, turning some on and off
  • generating cells and tissues that can be used for treatment of injury or diseases

What are some ethical issues surrounding stem cell research?

  • Should human embryos be experimented on?
  • Where do these embryos come from?
  • Is a blastocyst considered a human being?
  • Who should benefit from the research?
  • Should the government fund the research?

Resources

1. http://stemcells.nih.gov/ ---- A listing of all the information about stem cells on the NIH Web site.

2. http://www.news.wisc.edu/packages/stemcells/ ----- The University of Wisconsin's Web site about stem cells, written for general audiences.

3. http://www.stemcellresearchfoundation.org/ --- Stem Cell Research Foundation - has some good animations