Stem cells and cloning 0 by i9GHcN


									Cloning and Stem Cells
A wood panel painting
(~1500A.D.) depicting the
limb transplantation miracle
by Saints Cosmos and
Damian. According to legend
Cosmos and Damian were
physicians who successfully
transplanted the limb of a
dead Moor onto a patient
whose leg required
   Can we regenerate parts of the body?

• Red Deer replace their antlers every year. It takes
       ~3 months.
• We replace our blood cells. ~100 million /hour
• If part of the human liver is removed, it will re-grow
• Salamanders and Newts can re-grow their limbs
   •Video – newt limb regeneration

In general:
  regeneration in vertebrates doesn’t
                       work very well

Limbs and most organs aren’t replaced
Can cells be reprogrammed?

Experimental Example: Amphibian tadpole:
Preprogrammed Muscle cells were transplanted
into gut region of cells in the embryo but they
stayed as muscle cells.

Cells are programmed and “know’ what they
will become if the cells stay intact. How?
          “Central Dogma”
DNA             RNA             protein

DNA in the nucleus expresses genes→
makes RNA → RNA makes proteins.

Some of that protein goes back into the
nucleus and programs the cells to keep
making more of their kind.
        What is a Stem cell?
A cell of an embryo
• Can reproduce itself
• Can enter a differentiation pathway
  whereby one of its daughters is
  differentiated and the other stays an
  undifferentiated stem cell (totipotent)
 Totipotent: Having the ability to differentiate
 into ALL cell types.

 For example, the zygote and early embryonic
 cells are totipotent since they can differentiate
 into any cell type during development.
Pluripotent: Having the ability to differentiate into
many cell types.

In Mammals, embryonic stem cells are pluripotent,
and came from totipotent cells. They can
differentiate into various fetal or adult cells.
Where do we get stem cells?
Stem cells can be found naturally in
1) A Fertilized Egg
    (embryonic stem cells (ES)):
   150 cells called (blastocyst) contains two types
   of cells:
   1) trophoblast       2) inner cell mass

    Embryonic stem cells are obtained from the
   inner cell mass.

   Video: (human emb. development)

    A reliable stem cell reference:
  Other ways to get stem cells:
2. Cancers can form a variety of cell
   (connective tissue, cartilage, blood cells)
   can be transplanted into host       Ovarian cancer stem cells
   animals and in some cases turn into
   non-cancerous normal cells
3. (Since 1981)
   Start w/ an embryo.
   Blastocyst cells can be put in culture and
     grow indefinitely.
   When put into a host they will differentiate
     into a variety of cells.
  Stem cells are found in small numbers in
  various tissues in the fetal and adult body

    • blood stem cells are found in bone
    marrow → give rise to all specialized
    blood cell types.
    • newborn baby: umbilical cord,
    possibly baby teeth and amniotic fluid

These adult stem cells are multipotent – able to
differentiate into a limited number of cell types.
Stem cells tend to make a
heterogeneous collection
of differentiated cells

Video: creating lines

We haven’t figured out how
to make stems cells
differentiate into every
single type of tissue.
     Advantages of Embryonic Stem cells
• Capacity for indefinite proliferation in
• Can be differentiated into a variety of
  cells including germ cells
• Can be maintained as frozen stocks

   –Undergo spontaneous genetic changes
   –Hard to make into certain cell types (e.g. pancreas) (nerve
   tissue is fairly easy to make, however)
   –Immuno-rejection unless patient is immuno-suppressed. (not
     Nuclear reprogramming and
        Therapeutic cloning
• Can we make
  embryonic cells from
  cells (of the same
• This would avoid the
  problem of immuno-
 Somatic Cell Nuclear transfer
1. Start with egg (frog, mouse, human)
2. Use UV to kill pronucleus (egg chromosome)-left
   w/ cytoplasm
3. Pick up another cell in a way such that the cell
   wall is broken but intact nucleus (using a special
4. Inject the intact nucleus into the cytoplasm-only
   egg cell. The cell thinks It’s been fertilized. It
   starts to grow into an embryo and then an adult.

 •This cloning is inappropriate in humans (called
 reproductive cloning) video: SCNT

       Problems w/ SCNT
   (somatic cell nuclear transfer)
• Some transplanted nuclei show a long-
  term memory of their original gene state
  so they won’t allow reprogramming.
• only about 1/3 of nuclear transplants work

    However, we’re making progress!
              Legal Issues
In the United States, as of July 2011:
• it is illegal to use federal funding for
  research on human embryos derived from

• It is legal to use federal funding for
  research on embryos derived from IVF, if
  those embryos are not going to be used
  for anything else (like making a baby).
         Long-term Goal
Reprogram cells without having them go
  through a nuclear transfer to an egg
  In the news:

Sept. 2007 “Researchers
  Isolate Adult Stem
  Cells for First Time in
  Tendon tissue” (adult

 Maybe a cure for Alzheimer's disease,
 Parkinson's disease, and spinal cord injury,

  Lots of stories out there….
   Induced Plueripotent Stem cells (iPS)
    also called Adult Stem cells

iPS cells from adult human cells
Developed by two independent research teams:

James Thomson and colleagues at University of

Shinya Yamanaka and colleagues at Kyoto
University, Japan
    5 Common Ethical Objections
• Slippery slope – where do you draw the line
      between frogs & mice, and humans
• Cloning is unnatural. (Antibiotics are unnatural
• Killing of a potential life. “An embryo = a human
      being” Actually, an embryo would never
      progress until it is put into a womb.
• God intends humans to suffer – we need to
      have diseases.
• It’s good for us to see how others tolerate
(2)Transfect stem cell-               (3)Harvest and culture cells
associated genes into the cells       according to ES cell culture, using
by viral vectors. Red cells are       mitotically inactivated feeder cells
successes!                            (lightgray)

                                       (4)A small subset of the
                                       transfected cells become
(1)Isolate and culture donor cells.    iPS cells and generate ES-
                                       like colonies.

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