Stem Cells and Cloning Flashcards
What are the properties of embryonic stem cells
When fertilised embryo reach the blastocyst stage it forms an inner cell mass, and have unique properties
Immortality
Unspecialized
Developmental Potential (POTENCY)
Discuss ES cell division
Symmetric Cell Division - mitosis, undergone by differentiated cells as well as stem cells
Asymmetric cell division - divides into 2 cells; 1 = self-renewing cell, 2 = differentiated progenitor cell
They can differentiate into different types of progenitors (developmental potential/potency)
Discuss derivation of human stem cells
ESC’s are derived at a developmental stage before implantation
Fertilisation occurs in the oviduct, and a series of cleavage stages occur as it travels down
Each cleavage-stage embryo (blastomere) is undifferentiated and has potential to give rise to any cell of the body
1st differentiation event at ~5 days
Outer layer of cells committed to becoming part of the placenta (trophectoderm) separates from inner cell mass (ICM)
ICM cells have potential to generate any cell type of body
Cultured ICM cells continue to proliferate & replicate indefinitely, maintaining developmental potential to form any cell type of the body
Removal and culturing allows them to replicate indefinitely
These pluripotent, ICM-derived cells are embryonic stem (ES) cells
Discuss how stem cells can differentiate
ESC’s remain undifferentiated (unspecialized) in culture
If cells are allowed to clump together to form embryoid bodies, they begin to differentiate spontaneously
They can form muscle cells, nerve cells, and many other cell types - uncontrolled
Directed Differentiation
Change the chemical composition of the culture medium
Alter the surface of the culture dish
Modify the cells by inserting specific genes
Discuss directed differentiation
Directed Differentiation
Change the chemical composition of the culture medium
Alter the surface of the culture dish
Modify the cells by inserting specific genes
Discuss sources of embryos for hESC’s
Two groups obtained the ES cells from different sources:
ICM from IVF embryos-
Primordial germ cells from Aborted Fetuses
Both sets of hESC lines were capable of differentiating into cell types of all the major tissues representing the three primary germ layers (mesoderm, ectoderm, and endoderm)
Questions of ethics arise because embryos are destroyed as the cells are extracted, such as: When does human life begin? What is the moral status of the human embryo?
What are sources of stem cells in adult tissues and what are their limitations
These can be found in the brain, muscle, liver, retina, hair follicle, adipose tissue
Critical for maintenance of tissues
Responsive to injury and trauma
Illuminate our understanding of cancer
Adult stem cells are not as potent as ESC
Relatively rare un-differentiated cells found in many organs & differentiated tissues
Limited capacity for both self-renewal (in the laboratory) & differentiation
Differentiation capacity usually limited to cell types in the organ of origin
Discuss developmental potential of stem cells
Totipotent - fertilisation, as a zygote , can form embryonic and extra-embryonic tissues e.g. placenta
Pluripotent - once implanted forms a blastocyst with the inner cell mass and 3 germ layers
Multipotent - after differentiation, includes adults SC’s
Oligopotent - blood cells, can only differentiate into a very specific lineage
Unipotent - can self-renew but only differentiates into one cell type
Discuss nuclear reprogramming
As cells become more specialized they undergo epigenetic changes (DNA methylation and Histone modification)
This results in a specific pattern of gene expression in a differentiated cell that gives it the characteristics of that particular cell type
But is it possible to redirect the gene expression to that of a different cell type
Reprogramming backwards
Induced pluripotent cells
What are the types of stem cells
Embryonic
Adult
iPS
Nuclear transfer embryonic stem cells - derived form therapeutic cloning
What is the difference between fertilisation and cloning
Fertilised embryo - combined genetic material of parents
Clonal embryo - genetically identical to donor
How does cloning occur
Donor (what you want to clone) and recipient
Enucleate the recipient oocyte
DNA stain localises the genetic material, which is then removed
Prepare the donor nucleus from the donor cell and transfer into the donor egg
Apply electricity which starts cell division
The epigenetic marks needs to be removed from the donor DNA - needs to undergo nuclear reprogramming
This can occur when it is under the right conditions - in oocytes
What are the problems with cloning
Dolly 1/276 attempts - Success rate 1-3% V IVF success rate 20-50%
30% clones born alive have “large-offspring syndrome”
Likely due to incomplete reprogramming
Serious inexplicable respiratory or circulatory problems, which causes them to die soon after birth
Very few clones actually survive to adulthood
Discuss reproductive V therapeutic cloning
Reproductive cloning - produces a clonal embryo which is implanted in a womb with intent to create a fully formed living offspring - a clone
Embryo implanted
Therapeutic cloning - produces a clonal embryo, but instead of being implanted in a womb and brought to term it is used to generate stem cells
Embryo is cultured and grown into ES cell lines, can be used to be transplanted back to the patient
What is therapeutic cloning
Purpose
Find cures and therapies for diseases
Awaken the natural capacity for self-repair that resides in our genes
Potential Results
Patients will receive own stem cells to treat disease
No need for donor match if using ASC/iPSC
Like transplantation, but without rejection
