Stem Cells

• Stem Cells

  • Embryonic Stem cells:
  • Form when zygote starts to divide
  • Differentiate into special embryonic tissues
  • Produce completely viable organism
  • Adult Stem Cells:
  • Hide to protect from UV radiation or mutations
  • Divide/specialise to repair differentiated cells lost in wear/tear, injury or disease
  • Hemopoietic stem cells:
  • Found in red bone marrow
  • Differentiate into various blood cells
  • Unspecialised/undifferentiated
  • Divide by mitosis repeatedly for long periods
  • In plants = meristematic
  • Differentiation (specialises):
  • Some genes are “switched off” and others expressed more
• Cell Fate

  • Stem cell “makes decision” to differentiate into mature cell
  • Environmental signals converge on cell, activating signalling cascade leading to gene expression
  • Specific proteins change phenotype to specialised cell
  • Cell fate decision:
  • Describes stem cells exposure to different external/internal environments
  • Activates transcription/translation of different genes
  • Producing multiple, specific end-stage phenotypes
• Collecting stem cells

  • After IVF many couples donate their unused embryos for stem cell research
  • Scientists get embryos is therapeutic cloning
  • Merges cell (from patient who needs stem cell therapy) with donor egg
  • Growing
  • Scientists remove them from blastocyst
  • Grow them in nutrient-rich solution in petri dish
  • Stem cells divide several times
  • Scientists divide population to other dishes
  • After several months, there are millions of them
  • If they continue to grow without differentiating, it is a stem cell line
  • Can be frozen and shared between labs
  • Necessary for developing therapies
• Potency

  • Totipotent (omnipotent):
  • Develop into any cell
  • Useful in embryonic development
  • Can form completely viable organism
  • Developing embryos are entirely totipotent for first few weeks
  • Eventually, begin to specialise
  • Into each lineage (1 cell for digestive system, etc)
  • Pluripotent:
  • Stem cells derived from totipotent
  • Form inner cell mass in embryo
  • Differentiate into nearly every cell type
  • Unipotent:
  • Adult stem cell repair kit
  • Only produce one cell type
  • Can self-renewal (mitosis)
  • Induced pluripotent:
  • De-aged adult stem cells
  • Almost as useful
• Controversy

  • Stem cell research is a big issues dividing scientific and religious communities
  • Where does life begin?
  • Scientists have to use an already conceived embryo or clone one from patient's cell and a donated egg
  • To harvest stem cells, scientists must destroy it
  • Although embryo it may be 4-5 cells, some religious leaders it is equivalent of taking a human life