Normal Control of Cell Growth and Differentiation Flashcards
Morphogenesis definition
The biological process that causes an organism to develop its shape. Process controls the spatial distribution of cells during the embryonic development of an organism.
three types of tissue
renewing and resting and non dividing
Renewing tissue definition
Tissue that continually divides, such as skin with many stem cells
Resting tissue
terminally differentiated, cells multiply only to repair damage- hepatocytes will only divide to repair damaged tissue
Non dividing tissue
Terminally differentiated, cells will not multiply after birth- neurons, cardiomyocytes
What does cell growth require?
Increase in cell mass and volume caused by macromolecular synthesis and relative movement of the cell surface.
What controls cell growth and division?
Growth factors that drive proliferation and often act as mitogens
How is hyperplasia prevented?
Cell growth balanced by cell loss and cell death
How is organ size regulated?
Non autonomous control, release insulin like growth factor signalling controls. Thought that organs have a set point of growth, however in different organs the compartment size Is sensed and correspondingly adjusted.
Lack of a set point suggests that growth is driven by an autonomous program, insensitive to compartment size.
Evidence to suggest organ size regulation is autonomous
Transplant many fetal thymuses into developing mice; each grows to the same size.
Evidence to suggest organ size regulation is non autonomous
transplant fetal spleens into developing mice; each grows to a different size
Apoptosis definition
Death of cells that occurs as a normal and controlled part of an organism’s growth or development. Programmed cell death
What biochemical events characterise apoptosis?
Blobbing, cell shrinkage, nuclear fragmentation. chromatin condensation and chromosomal DNA fragmentation
What are apoptotic bodies and what happens to them?
Apoptotic cell fragments into vesicles engulfed by phagocytic cells before bioactive contents can spill out and cause damage.
Stem cell definition
Undifferentiated cells that are capable of renewal and can divide without limit- produce more specialised cells
Two different ways cells are born
exponential, rapid clonal expansion (cell division) or initiating the differentiation of new stem cells
Different types of stem cell + definition + example
totipotent- capable of differentiating into all cell types- fertilised egg, morula
pluripotent- capable of giving rise to several different cell types- embryo- give rise to ectoderm, mesoderm and endoderm
multipotent- capable of giving rise to multiple specialised cell types present in a specific tissue or organ
unipotent- has the capacity to differentiated into only one type of cell- skin cell
Cell potency definition
The cell’s ability to differentiate into other cell types
Committed stem cell definition
can give rise to a smaller subpopulation of cells
Explanation of cell renewal in epithelium
Stratum basalum contains proliferating stem cells
Cells move through the different layers of skin, differentiating as they do so, and become sloughed off at the surface
Reach terminal differentiation at the stratum corneum
Do stem cells divide often? + why?
No, limit the potential mutations during DNA replication and remains potential for rapid replication at the site of wound repairs
What else is present in the skin + function?
Transit Amplifying Cells which are an undifferentiated population in transition which enable tissue regeneration to proceed- bottle neck effect- once the TAC pool forms the regeneration will proceed without return
What is the common stem cell in blood?
Multipotent haemopoietic stem cell
Examples of blood cells that form
Leucocytes- T cells, B cells, neutrophil, eosinophil, basophil
erythrocytes
platelets, mass cells, osteoclasts, mast cells
Evidence for the multi potency of mice
Irradiate the mice, halting blood cell production
Inject bone marrow cells from healthy donor
mouse survives as the injected stem cells colonise its haematopoetic tissue
Bone marrow transplant used to treat…
severe aplastic anaemia, leukaemia, non-hodgkin’s lymphoma
Induced Pluripotent Stem Cell definition
A type of pluripotent stem cell that can be generated directly from adult cells
Explain how cells are reprogrammed into stem cells
Shinya Yamanaka added four reprogramming factors, Oct4, Sox2, Klf4, and c-Myc, into fibroblasts
Delivered by viral vectors, which reverted the genome to its pluripotent state
Why are IPS cells important?
Able to generate any cell type, especially important as it can produce new neurons, which normally don’t proliferate- show potential in treating Parkinson’s disease
Similarities between differentiated cells
Similar set of organelles, express some common proteins from housekeeping genes
Differences between differentiated cells
express cell specific proteins not expressed in undifferentiated cells which lead to specialised functions and structures
When does differentiation take place?
During the cell cycle, often before S
What produces cells with different functions?
Different genes are expressed- euchromatin whilst others are silenced- heterochromatin, so different proteins are produced . However genome is not altered in sequence
Fate definition
Fate of a cell describes what it will become in the course of normal development
How is the fate of a particular cell determined?
Label the cell and observe what structures it later becomes apart of.
Determination of a cell definition
Involves progressive restrictions in a cell’s potency. The cell ‘chooses’ a particular fate however it still looks the same to its undetermined neighbours. Implies a stable change, the fate of the determined cell does not change.
A committed cell definition
Cell is not yet determined, so its fate could be changed
What is cellular differentiation controlled by? + explanation
Cellular signals, mainly growth factors. Often the steps are as follows:
- Ligand produced by a TAC binds to a receptor on an extracellular region of the cell
- Receptor undergoes a conformational change
- this changes the shape of the cytoplasmic domain, acquiring enzymatic activity
- Receptor catalyses reactions that phosphorylate other proteins, activating them causing a phosphorylation cascade
- Eventually activates a dormant transcription factor thus contributing to differentiation
Also controlled by epigenetics
How is determination and commitment shown in the trilaminar disc?
Ectoderm upon mesoderm upon endoderm.
If mesoderm is removed, the ectoderm in contact with endoderm will become mesoderm, suggesting that the endoderm is determined, whereas the ectoderm is not and ligands are released from the endoderm
