Stem Cells Flashcards
What are stem cells?
A stem cell is the most immature cell type
What are the 3 key features of stem cells?
- They have the ability to self-renew and replace themselves.
- Stem cells are the only cell type that have the potential to differentiate into any cell type (multi-potent).
- They can enter quiescence when not needed (reversible step in cell cycle - G0).
What are the 2 different ways stem cells can undergo self-renewal?
A stem cell can divide in two ways:
- Asymmetrically: Produces one identical copy of the parent cell and one slightly differentiated progenitor cell.
- Symmetrically: Produces two stem cells identical to the parent cell.
What form are stem cells normally in?
Stem cells only function when they are needed and are mostly in a quiescent state, waiting for an external signal to divide.
What is the importance of quiescence?
Quiescence reduces the number of divisions to protect the genome from DNA damage.
How are stem cells capable of mass cell production?
They go through a stage known as transit amplifying cells, replicating transiently to avoid compromising the stem cell population.
Define potency.
Potency refers to how many cell types a stem cell can give rise to.
What does the potency of a stem cell depend on?
The potency of a stem cell depends on its origin.
What are the 4 levels of potency?
- Totipotent: Can differentiate into any and all cell types.
- Pluripotent: Can differentiate into all cell types of the embryo but not into an entire organism.
- Multipotent: Can differentiate into 2 or more cell types within a specific tissue.
- Unipotent: Can only differentiate into a single cell type.
What happens to potency as the embryo grows?
As the embryo develops, stem cells lose potency and can only differentiate into specific tissue lineages.
What is the potency of a zygote?
The zygote is totipotent and can give rise to every cell type.
When does the zygote become pluripotent?
The zygote becomes pluripotent after the 8-cell stage.
What is the potency of adult stem cells?
Adult stem cells are multipotent.
Where are embryonic stem cells derived from?
Embryonic stem cells are derived from the inner cell mass of the blastocyst.
Define stem cell niche.
The stem cell niche is the tissue or organ where the stem cell is present, and its growth is dependent on this niche.
What do stem cells require to maintain themselves?
Stem cells require signals from a specialized niche that provides necessary signals for maintenance.
What governs the concentration gradient of signals in the external environment of stem cells?
The extracellular matrix governs the concentration gradient of extracellular signals that stem cells are sensitive to.
What are the differences between adult and embryonic stem cells?
Embryonic stem cells are derived from early embryos and have more potential than adult stem cells, which arise in the fetus and maintain organs throughout life.
What are the challenges of adult stem cells?
- Stem cells are rare.
- Cells within adult tissue are heterogeneous.
- Some adult tissues are inaccessible for isolation.
- Removal from the niche can change stem cell properties.
- Stem cell number limits applications.
- Not all tissue stem cells are well characterized.
What are the limitations to allogeneic bone marrow stem cells?
We cannot force people to donate their bone marrow, necessitating the need to find ways to make stem cells in vitro.
What causes sickle cell disease and what is the only cure?
Sickle cell disease is caused by a homozygous single point mutation in HBB, and the only cure is a stem cell transplant.
How does hemoglobin switch during development?
Hb switches from embryonic to fetal Hb as the gamma globin gene is switched on, and at birth, the gamma globin gene is switched off while the beta globin gene is switched on.
How can sickle cell disease be corrected?
- Fix the point mutation using CRISPR Cas9.
- Keep fetal hemoglobin in adult cells by targeting protein BCL11A.
What is a downside of CRISPR?
The cost is approximately $2 million per patient.
