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.
