p2 Flashcards
contact inhibition
While the cell bodies of neighboring cells may cross each other, their nuclei never overlap. Once cell reaches confluence, contact inhibition signals cells to stop growing
Confluence
the percentage of the culture dish surface covered by a layer of adherent cells, with 100% confluence meaning the dish is fully covered with no gaps between cells.
Quiescence
Growth arrested cells
This is the case in mammals everywhere but the epithelial tissues of the intestines
Cells in vitro have undergone treatments and divide unlike their quiescent counterparts
What is purposeful cell death for
- Provide space for cell growth
- No longer needed
- Infection
Types of apoptosis
Extrinsic - mediated by death receptor
Intrinsic: stress signals cause
Cell growth system controls
Positive factors: promote increasing cell mass/cell division, suppress cell death
Availability of nutrients, growth factors, mechanical tension through the cytoskeleton and surface adhesion
Negative factors: promote programmed cell death, suppress growth
Sensing presence of death signal, apoptosis-triggering stress
G0 cell cycle
Proliferative cells go through the G₁, S, G₂, and M phases of the cell cycle
Quiescent cells exit G₁ and enter G₀:
G₀ can be reversible and the differentiated cells returned to the G₁ phase (e.g., hepatocytes), or irreversible for terminally differentiated cells (e.g., nerve cells)
Major professional secretory cells in the human body (hepatocytes, plasma and pancreatic cells) are at G₀ phase
What regulates the cell cycle
The progression of the cell cycle is regulated by different cyclins, Cdks, and CDI inhibitors, each of which is dynamically expressed
Pluripotent
Can make all types of specialized cells in the body
Embryonic stem cells are pluripotent
- Pluripotent stem cells can form all three germ layers including germ cells, but not the extraembryonic tissue as placenta and umbilical cord. Cells of the inner cell mass of the blastocyst are pluripotent. When these cells are brought into culture, they are called embryonic stem cells (ESCs).
Totipotent
- Totipotent stem cells can form an entire organism. The fertilized oocyte and the cells after the first cleavage divisions are considered totipotent.
Multipotent
Can make multiple types of specialized cells, but not all types Tissue stem cells are multipotent
Oligopotent
- Oligopotent stem cells can differentiate into two or more lineages, for example, neural stem cells that can form a subset of neurons in the brain.
Unipotent
Unipotent is the ability to form cells of a single lineage, for example, spermatogonia stem cells.
Potency
Measure of how many types of specialized cell a can make
Morula and blastula
- Early development starting from the fertilized egg (zygote)
- The zygote then forms the morula, a solid ball of cells which then forms a fluid-filled space termed the blastula, where the outer layer is composed of trophoblasts that will form the placenta and an inner cell mass that will form the embryo.
Mesoderm
- The cells between the inner and outer cell layers are known as
the mesoderm and will form most of the internal organs. - At this stage, cells from one presumptive layer are not yet determined to be ectoderm, mesoderm, or endoderm as transplanting cells from one layer to another, the cells will adopt the phenotype of the layer to which they are transferred.
Stem cell categories
- Stem cells can proliferate and differentiate to become cells with new phenotypes and functions.
- The field can be divided into adult, embryonic and induced stem cells
What can happen when SC divide (2 options)
They self-renew or differentiate into specialized
cells
Blood stem cells
Individual white blood cells live for 1-3 days, and all your red blood cells are replaced every 120 days by hematopoietic stem cells (HSCs) in the bone marrow.
Do cardiomyocytes regen?
Yes but cardiomyocyte turnover is very slow, and a 50-year-old person has replaced only about half of his/her cardiomyocytes present after their first birthday.
Central nervous system regeneration?
The central nervous system—brain and spinal cord—was thought not to regenerate but research over the last 15 years has shown the cells of these tissues may renew slowly.
Skeleton regeneration rate and cells
Your whole skeleton is replaced every 6–8 years by the combined actions of the osteoclasts which remove and remodel the calcified bone matrix, and the osteoblasts which divide and then differentiate into new osteocytes and produce extracellular matrix which becomes cross-linked and calcified over time.
induced PSCs
Adult somatic cells can be isolated and reprogrammed by transfection with a combination of immortalizing genes to produce the induced pluripotent stem cells (iPSCs)
Self-renewal
Self-renewal refers to the ability of a stem cell to divide and make identical copies of itself to assure that the stem cell population is not depleted, and exists throughout development, and some may remain for the life of the organism.
Self-renewal in vivo requires a specialized location—the stem cell niche—where stem cells are maintained through the action of support cells nearby.
Asymmetric division
- Self-renewal allows the proliferation of stem cells, or it can produce one daughter cell that is a stem cell and one daughter cell that then proceeds along a differentiation pathway.
- This asymmetric division may be caused by cell fate transcription factors accumulating unequally in one daughter cell or can be caused by signals outside the cell, such as another cell or a gradient of morphogens, or growth factors from the nearby tissue.
Why self-renew and differentiate
1 stem cell
Self renewal - maintains the stem cell pool
4 specialized cells
Differentiation - replaces dead or damaged cells throughout your life
TACs
most rapidly dividing cells are the transit-amplifying cells (TACs)
Time differentiation SCs
20-30h
How many SCs one cell make
A single cell dividing every 24 h can produce 1 million cells in 21 days and 1 billion (109) in 31 days.
EpSC
epidermal stem cell
cryopreservation
Freezing (here stem cells) to keep for later
With SCs we use dimethylsulfoxyde to prevent formation of ice crystals breaking the membrane
Passaging
The cells in the culture vessel must be subcultured into two to four new culture vessels with fresh nutrient medium.
* This step is referred to as “passaging” the stem cells, and each passage usually represents three to four doublings of the stem cells.
* Stem cells are often cultured this way to keep them in log phase growth to produce millions of cells in a predictable time period.
Cell division and cell human numbers
A single cell dividing every 24 h can produce 1 million cells in 21 days and 1 billion (109) in 31 days
30 cell division cycles represent 1,073,741,824 or ∼1 billion cells
There are approximately 37 trillion cells that make up the human body
Stem cell differentiation and cause
- Differentiation is the process whereby stem cells become more specialized cell types and can perform new functions by expressing new genes, mRNA, and proteins.
- Differentiation involves the deactivation of some genes and the activation of a new set of genes.
- Differentiation can be caused by a change in basal nutrients, a change in the cell’s environment, a stimulation, or a lack of stimulation of a signaling molecule, a new cell-to-cell interaction, etc.
Zygote
Definition: A fertilized egg formed when DNA from both parents’ genetic material combines. Marks the beginning of embryonic development.
Blastomeres
Definition: Cells produced by the division of a zygote. Early embryonic cells during the initial stages of cell division.
Morula
Definition: An early stage embryo consisting of 16 totipotent cells, forming a solid ball without an internal fluid compartment. Leads to the differentiation of outer cells into trophoblasts and inner cells into progenitors.
Blastocyst
Definition: An advanced stage in embryonic development characterized by a fluid-filled internal cell mass. The outer cells (trophoblasts) contribute to forming the placenta, while the inner cells give rise to the embryo. It’s the stage used for embryonic stem cell collection and typically for implantation in IVF.
Embryonic Stem Cells
Definition: Pluripotent cells derived from the inner cell mass of the blastocyst, capable of differentiating into any cell type, thus holding potential for regenerative medicine and research.
Endoderm
Definition: One of the three primary germ layers in the embryo that forms the innermost layer. Gives rise to the digestive tract, liver, pancreas, and other internal organs.
Ectoderm
Definition: The outermost germ layer of the embryo. It develops into the skin, brain, nervous system, and other external tissues.
SC differentiation def and causes
Process whereby stem cells become more specialized cell types and can perform new functions by expressing new genes, mRNA, and proteins.
(deactivation of some genes and the activation of a new set of genes)
Can be caused by a change in:
- basal nutrients
- cell’s environment
- stimulation, or a lack of stimulation of a signaling molecule
- new cell-to-cell interaction
Where are embryonic vs tissue stem cells found
embryonic in the early blastocyst, tissue in fetus, baby and adult
Whats homeostasis in terms of stem cells
requires the loss of cells to be accurately balanced by cell replacement.
Stem cell proliferation
Proliferation of stem cells allows the single cell zygote—the ultimate stem cell—to grow into an adult organism.
* During this time, tissues and organ systems develop and become fully functional.
