Stem cells

• Stem Cell


  A type of cell that has the ability to develop into different cell types
• Characteristics of stem cells

  • Potency
• Types of Stem Cells

  • Totipotent
  • Pluripotent
  • Multipotent
• Totipotent


  • Each cell can develop into a new individual
  • Cells from early (1-3 days) embryos

  
• Pluripotent


  • Cells can form any (over 200) cell types
  • Some cells of blastocyst (5 to 14 days)
• Multipotent


  • Cells differentiated, but can form a number of other tissues
  • Foetal tissue, umbilical cord blood, and adult stem cells
• Embryonic stem cells


  • Can generate every cell in the body including the placenta and extra-embryonic tissues

  
• Induced pluripotent stem cells

  • Cannot form the entire human being
  • Can generate every cell in the body except placenta and extra-embryonic tissues

  
• Adult stem cells


  • Become specific cell types; may or may not have plasticity

  
• Stem cell therapies


  • Bone marrow transplants
  • Umbilical cord blood stem cells
• ‘Therapeutic cloning’ involves somatic cell nuclear transfer

  
• In 1997 Ian Wilmut and colleagues cloned Dolly the sheep

  
• Dolly arose by a process called somatic cell nuclear transfer


  This type of cloning in mammals is a difficult and inefficient process

  
• Therapeutic cloning


  1. Transfer nucleus from adult cell

  2. To enucleated egg

  3. Resulting embryo produces differentiated cells for transplantation therapy

  4. Bypasses the problem of tissue rejection

  
• Problems to be overcome in embryonic stem cell research include ethical issues
• The Ethical Debate


  • In favor of ESCR
  • Against ESCR