Topic 24 - Stem Cells Flashcards
Sperm fertilizes the egg to form
The first stem cell
Totipotent
First stem cells that can develop into any type of cell in the body (including placenta)
First stem cells that can develop into any type of cell in the body (including placenta)
Totipotent
First cell divides into
Two totipotent stem cells
If separated and implanted after IVF, each cell will devlop into
A human
If separated naturally and implanted, each cell develops into
Identical twins
Cells continue to divide to yield a small hollow sphere of cells known as
Blastocyst
Human embryos normally reach the blastocyst stage
5-7 days after fertilization
In IVF clinics, human embryos are implanted at the
Blastocyst stage
Excess embryos are
Either discarded or frozen for later use
Blastocyst-cells specialized and turn into
Pluripotent stem cells
More limited developmental potential
Pluripotent stem cells
Potential to develop into any cell of the human fetus but not the placenta
Inner cell mass
Develop into placenta and supporting tissues but NOT the fetus
Outer layer cells
Unlimited capability to develop into all extra embryonic, embryonic, adult types of cells
Totipotent Stem Cells
Extensive but limited capability, can develop into most types of cells in an organism
Pluripotent Stem Cells
Divide and change their own gene expression
Totipotent
Give rise to pluripotent stem cells
Totipotent
Stem cells divide and yield other pluripotent stem cells more specialized committed stem cells
Pluripotent
Ex. Blood stem cells
Pluripotent
“Committed” stem cells that divide and yield only specialized cells
Unipotent Stem Cells
Exist in the adult human body and constantly replace cells of the blood, intestine, and skin
Pluripotent and Unipotent
Cell therapy
Bone Marrow
Blood and immune system cells
Bone marrow hematopoietic stem cells
Bone, cartilage, fat, fibrous connective tissue
Bone marrow stromal stem cells
Adult cells that have been reprogrammed to become stem cell like
Induced pluripotent stem cells (iPS)
Fully differentiated cells that are turned into pluripotent cells
iPS
Different than “adult stem cells” because these cells have genes added to them
iPS
Inner cell mass can be removed from human blastocyst stage embryos and cultured in
dishes
Cells reproduce and maintain
pluripotency
Controversy
Destroys “excess” human embryo life
In most IVF clinics these are discarded anyway
Somatic cell nuclear transfer (SCNT) Process
- Unfertilized egg is removed from adult female
- The DNA is removed
- The nucleus from a somatic cell is put into the egg
- Embyro is devloped into a genetic copy of the somatic cell
- ESCs can be isolated from the embryo
Adult tissue
Somatic cell
Dickey-Wicker amendment
1995 - Prohibits federal funding to support the creation of human embryos for research purposes
Still in effect
President Bush
2001 - executive order that the government will support research only on existing stem cell lines (about 12 available), but not production of new lines
Existing stem cell lines were initially grown on
Mouse feeder cells
Problem with mouse feeder cells
Could be contaminated with mouse genes or viruses and not useful for treating humans
President Obama
2009 - overturns Bush ban on using funds for new stem cell research
Current Policy
Allows federal support of research on current lines or new lines developed with non-federal support
To better understand normal human development - birth defects
Basic Research
Increase effectiveness and decrease side effects - personalized medicine
Drug Testing
Source of pluripotent cells to treat type 1 diabetes, heart disease, neurological disease, etc.
Cell Therapy
Embryonic stem cells can be
Expanded in cultures - few cells divide to provide many
Stimulated to specialize into different types of human cells - ex. insulin-secreting pancreas cells
Type 1 Diabetes
Loss of insulin-secreting Beta cells from pancreas leading to insulin deficiency
Require for uptake of glucose into muscle and other cells
Insulin
Lack of insulin
Build up of toxic levels of glucose in blood
Cultured beta cells produce and secrete
insulin
Death of dopamine secreting neurons in specific region of the brain
Parkinson’s Disease