chapter 10: stem cells Flashcards
what are the three unique properties of stem cells?
-
stem cells are unspecialised cells in the body
- stem cells do not have any tissue-specific functions that allow them to perform specialised functions -
stem cells are capable of long-term self renewal by dividing via mitosis
- stem cells can continue to divide many copies of itself by mitosis, yet remain undifferentiated -
under appropiate conditions, daughter cells of stem cells can differentiate into specialised cells of one or more types
- when a daughter stem cell receives specific signals, such as growth factors
- it switches on certain genes and begin to produce specific proteins
- which gives rise to specific structure and functions
- hence stem cells can give rise to specialised cells, replacing cells that are damaged or have died
what are zygotic stem cells?
- a zygote is produced from the fusion of an egg and a sperm cell
- it is a stem cell as it possesses the three unique properties of stem cells
- zygotic stem cells are totipotent
- totipotent: the ability to differentiate into any of the cell types that make up a whole organism
zygotic stem cells
what is the normal function of a zygote?
- the normal function of a zygote is to divide by mitosis to form a hollow ball of cells known as blastocyst
- the blastocyst then develops into an embryo
- the implantation of the blastocyst to the uterus wall then occurs where the blastocyst develops into an embryo
- which eventually gives rise to a growing feotus
blastocyst have extensions that reach deep into the uterine wall to ensure that the blastocyst is not discarded
- which can lead to miscarriage
what are embryonic stem cells?
- they are obtained from the inncer cell mass of blastocysts
- embryonic stem cells are pluripotent
- pluripotent: has the ability to differentiate into ALMOST any cell type to form any organ or type of cell
- EXCEPT cells from the extra-embryonic membranal tissues
what are the normal functions of embryonic stem cells?
- its normal function is to differentiate into different specialised cell types that forms the different tissues and organs in a developing feotus
sspecifically, ESCs give rise to the cells that form the three embryonic germ layers- endoderm, mesoderm annd ectoderm
- endoderm (internal layer): gives rise to the gut (pancreas, stomach, liver) & lungs etc
- mesoderm (middle layer): gives rise to muscles, bone, blood, connective tissues and heart
- ectoderm (outermost layer): gives rise to skin, nerve cells
all the different tissues and organs are then derived from the three germ layers of the developing embryo after multiple rounds of divising and differentiation
what is the medical application of embryonic stem cells?
- since embryonic stem cells are capable of self-renewal and are pluripotent
- stem cell therapies have been proposed for regenative medicine and tissue replacement after injury or disease
- diseases that could potentially be treater by pluripotent stem cells include a number of blood and immune-system related genetic diseases, cancers, juvenile diabetes, parkinson’s disease, blindness and spinal cord injuries
however, harvesting ES cells from human blastocyst is controversial because it destroys the embryo, which could potentially become a feotus
what are adult stem cells?
- they are stem cells found in already developed tissues or organs
- they are multipotent stem cells
- multipotent: ability to differentiate into a limited range of cell types or produce only cells of a closely related family of cells and so are not pluripotent or totipotent
some adult tissues and organs known to have stem cells are:
- brain
- bone marrow
- dental pulp of teeth
- endothelium
- skin
- skeletal muscles
- digestive system
- pancreas
- liver
what are the normal functions of adult stem cells and give me an example of adult stem cells
the normal function of adult stem cells are to provide new cells for:
- growth and development of organs and tissues
- replacement of cells that die due to injury or diseases
- thus repairing and maintaining the damaged tissues/organ in which the stem cells are found
example of adult stem cell-** lymphoid and myeloid stem cells**
- these are stem cells found in the bone marrow, particularly in the ribs, vertebrae, breastbone and pelvis bond
- the normal function of lymphoid and myeloid stem cells is to differentiate into mature types of blood cells
- eg. erythrocytes and leucocytes
- to replace the damaged blood cells
what is the medical application of lyphoid and myeloid stem cells?
- these stem cells have been used to treat leukemia
- in leukemic, bone marrow starts to make abnormal white blood cells that do not function normally
- bone marrow transplantation is used
- obtain lymphoid and myeloid stem cells from donor’s bone marrow
- transplant cells into the patient’s body intravenously
- use of chemotherapy and radiation to destroy abnormal stem cells in the patient’s bone marrow
- this makes room for the new stem cell that would be transplanted - stem cells will migrate into the patient’s bone marros, divide and differentiate into new, healthy WBCs to replace the abnormal cells
what are the advantages and disadvantages of using embryonic stem cells in research or medical therapy?
advantages
- pluripotent- able to differentiate into almost all cell types and tissues
- easy to identify, extract and grow in-vitro (in a laboratory)
- large numebr of excess fertilised eggs from IVF clinic, hence ease of availibility
disadvantages
- ethical concerns raised
- high possibility of immune rejection when stem cells from a donor ( which is non-genetically identical to patient) are introduced into a patient
- there may also be unknown long-term consequences to the well being of the recipients
what are the advantages and disadvantages of adult stem cells?
advantages:
- adult stem cells, and tissues derived from patients themselves are currently believed less likely to initiate immune rejection after transplantation as stem cells are genetically matched to patients
- also a patient’s own cells cound be expanded in culture, directed to differentiate into specific cell type and then reintroduced into the patient
- demonstrated success in some therapies
- no major ethical concers have been raised, no destruction of human blastocyst
disadvantages:
- multipotent: limited in the number and type of differentiated cells the stem cells can become, can only differentiate into cell types of their tissue of origin
- hence less flexible to derive preferred cell type
- difficult to identify, isolate and grow in cluture in a laboratory due to rare membres found in adult tissues
what are induced pluripotent stem cells? (iPSCs)
to overcome the ethical implication of human embryonic stem cell research, research has been conducted on induced pluripotent stem cells
- they are specilised/ differentiated somatic cells
- that have been DEDIFFERENTIATED / genetically reprogrammed to an embryonic stem cell-like state
- by being forced to express genes coding for transcription factors important for maintaining the pluripotent and self-renewing characteristics of embryonic stem cells
- since they are now embryonic stem cell-like
- they have the potential to differentiate into differentiate specialised cell types that form the different tissues and organs in a developing feotus
what is the significance of iPSC?
- since iPSCs can be derived directly from specialised cells, they bypass the need for human embryos, hence is less of an ethical consideration
- each individual could have their own pluripotent stem cell line, derived from their own specialised cells
- when used for medical treatment, there is less risk of immune rejection
- iPSCs also rather easy to create as the technique can be performed in any moderately equipped laboratory and does not require materials that are difficult to obtain like human embryos
what are the challenges associated with iPSC?
-the rate at which somatic cells are reprogrammed into iPSCs is low
- the low effiency rate may reflect the need for precise timing, balance, and absolute levels of expression of reprogramming genes
- viruses are currently used to intriduce the reprogramming factors into adult cells, and this process must be carefully controlled and tested efore the technique can lead to useful treatment for humans
- in animal studies, the virus used to introduce the stem cell factors sometimes causes cancers
- these viral vectores preferentially integrate into actvive genes and most of the introduced transcription factors possess oncogenic potentials
- eprsistent expression of these introduced genes might lead to uncontrolled cell division and risk of tumours
what is the process of iPSC like?
- remove one’s own specialised cells
- reprogram into embryo pluripotent stem cell-like in lab
- can differentiate into other type of cells
- transplant back into own body
- can be used to replaced damage tissue like damaged skin due to serious burns, damaged heart due to heart failure
- less risk of immune rejection
