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Stem Cells

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Title: Stem Cells


1
Stem Cells
  • What are they and what can we do with them?

2
Stem Cell Characteristics
  • They are undifferentiated cells that can divide
    indefinitely in culture.
  • They can divide asymmetrically producing one
    daughter resembling its mother and one that can
    differentiate into cells of all three germ layers
  • They must originate from an embryonic or adult
    stem cell
  • (New England Journal of Medicine. 349267-274.
    2003)

3
Types of Stem Cells
  • Embryonic
  • Umbilical
  • Adult

4
Embryonic Stem Cells
  • The first human stem cell lines were developed at
    the Univ. of Wisconsin in 1998. 14 blastocysts
    were donated by couples in an in vitro
    fertilization program. The lab established 5 cell
    lines. The cells were able to develop into
    various cell types including neural, gut,
    cartilage, muscle and bone.

5
Embryonic Stem Cells
  • are derived from fertilized embryos less than a
    week old, the blastocyst stage of development.
  • (Photo from www.time.com/time/2001/stemcel)l

6
Developmental Stages(Photo from J. Clinical
Investigation. 1141364-1370. 2004)
7
Morula Stage
  • A 32-128 solid ball of cells
  • Each cell is totipotent it can give rise to all
    embryonic cell types including extraembryonic
    tissues necessary for implantation and formation
    of the placenta and umbilical cord.

8
Blastocyst Stage
  • The blastocyst (3-5 days in humans) has two
    regions
  • the inner cells mass contains the
    undifferentiated stem cells that will form the
    organism
  • The surrounding cells (trophoblast) help form the
    placenta and umbilical cord

9
Inner Cell Mass
  • These cells are called pluripotent and will first
    form three germ layers (ectoderm, endoderm and
    mesoderm) through a process called gastrulation
  • The cells in each germ layer are now called
    multipotent and they follow a path of
    specialization to become progenitor cells which
    form specific cell types e.g. nerve or muscle
    cell

10
Pluripotent Cells(Photo from J. Clinical
Investigation. 1141364-1370. 2004)
11
Cellular Specialization
  • Cells become specialized as they occupy certain
    positions in an embryo at a specific time in the
    life of embryo
  • Specialization occurs as a result of the
    transcription of a specific set of genes in a
    cell to cause the translation of proteins that
    are unique to that cell type e.g. Dystrophin
    in muscle cells.

12
Stem Cells in the Lab
  • Currently, stem cells are grown in association
    with mouse feeder cells (fibroblasts) and animal
    proteins which form a matrix on which the stem
    cells grow
  • Feeder cells keep the stem cells in the
    undifferentiated state
  • Existing stem cells lines are contaminated with
    an animal protein

13
Stem Cells in the Lab
  • Scientists at WiCell Research institute recently
    published work that eliminates the need for
    feeder cells, one of the main sources of
    contamination with pathogens.
  • The research shows a protein called fibroblast
    growth factor 2 does the same job of the feeder
    cells keeping the stem cells undifferentiated.
  • Stem cell cultures still use Matrigel (a matrix
    of cells from mouse tumors and bovine serum
    replacement to keep the cells healthy.
  • (Nature Methods. 2185-190. 2005)

14
Stem Cell Images (http//www.news.wisc.edu/package
s/stemcells/3327.html)
15
Establishing Stem Cell Lines
  • Inner cell mass cells are transferred to culture
    dishes where they divide and spread over the dish
  • Subculturing transfers the cells to additional
    dishes after the first one is filled
  • After 6 months there are millions of cells
  • The cells are evaluated before being called a
    cell line

16
How Are ESC Identified(http//stemcells.nih.gov/i
nfo/basics/basics3.asp)
  • Growth and subculturing for many months
  • The presence of specific surface protein markers
    for undifferentiated cells
  • The presence of the protein, Oct-4, a
    transcription factor unique to ESC
  • Microscopic chromosomal examination
  • Subculturing potency after freezing and thawing
    and replating
  • Test for pluripotency

17
Test For Pluripotency(http//stemcells.nih.gov/in
fo/basics/basics3.asp)
  • Allow cells to differentiate spontaneously in
    cell culture
  • Manipulate cells to differentiate
  • Inject cells into immunosupressed mouse to form a
    teratoma (benign tumor containing many cell types)

18
Stem Cell Research
  • Other countries are beginning to take the lead in
    stem cell research Korea
  • Private companies in the US can do research with
    private funds
  • Universities are setting up labs supported solely
    by private funds- e.g. Univ. Wisconsin, Harvard
  • In 2004, Harvard produced 17 new human ESC lines
    using private funds

19
ESC Use in Basic Research(New England Journal of
Medicine. 349267-274. 2003)
  • Study unique aspects of early human development
  • Study origin and mechanisms of chromosomal
    abnormalities
  • Preclinical testing of candidate therapeutic
    drugs in many human tissue types

20
ESC and Treating Diseases
  • Animal experiments have shown the potential
    therapeutic value of stem cells
  • Mouse ESC have been induced to make
    dopamine-producing cells in rats with Parkinsons
    disease. The symptoms stopped and the rats lived
    up to 3 months. (Nature. 417online. June 2002)

21
ESC and Treating Diseases
  • Mouse ESC have been induced to differentiate into
    spinal cord motor neurons.
  • The neurons were injected into the spinal cord of
    a chick embryo and migrated to the proper
    location in the cord.
  • Some sent out axons to developing limb muscles
    and formed synapses
  • (J. Clinical Investigation. 1141364-1370. 2004)

22
Spinal Cord Experiment(photo from J. Clinical
Investigation. 1141364-1370. 2004)
23
Human Trials Considerations
  • How do we control the stem cells e.g. start and
    stop differentiation, direct cells to specific
    tissues
  • Risk of immune rejection
  • Prevent formation of tumors
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