Stem cells & Development Flashcards
Define differentiation
The process by which a cell undergoes a change to an overtly specialised cell type
What is determination?
Progressive restriction in developmental potential of different cell types through a cell’s pre-determined ‘fate’
When can we say that a cell has become determined?
when cells are moved to a different location continue to develop into their fate regardless
When is a cell specified?
- When isolated cells/tissues still form what they were originally meant to
- This means that the information needed is inherent
Define induction
Process by which one embryonic region interacts with a second region to influence that second region’s differentiation or behavior
What are the 3 types of cell signal?
Diffusion: where diffusible signal from one cell interacts with a receptor on the target cell, this can work at any distance
Direct contact: interaction of transmembrane proteins
Gap junction: movement of signals between connected cells
Give an example of induction
If animal cap cells are transplanted on to vegetal cells this induces the development of mesodermal tissue
What is competence
Whereby cells may only be able to transmit/receive signals for a short space of time
How do sea urchin studies show that the position of cells during early development is important?
- When removing most of the vegetal pole but transplanting micromeres on the bottom of the animal pole, can still make up for massive cell loss and develop normally
- When transplanting micromeres to the side cannot develop normally and a secondary gut is induced
- Example of indeterminate development
What is mosaic development?
Also known as ‘determinate’
When the separation of blastomeres results in incomplete parts of embryos and development is usually arrested
How can cell division differentiate cells?
- Uneven distribution of protein/RNA during cell replication can lead to inherent differences between cells
- Asymmetric cell division can also differentiate cells
Why is timing important?
Because even though early stages of development are regulative, lineages can become determined and invariant (animal and vegetal pole develop differently when isolated)
Give 6 tissue patterning signals
- Wnt
- TGFb
- BMP
- Hh
- Notch
- RTK
(Used by all multicellular organisms)
What is a morphogen?
A substance whose gradient/exposure time across tissues causes differences in differentiation
Describe the process of lateral inhibition
- Cell becomes specialised and releases long range signals to inhibit the activation of other cells to undergo the same activation in the nearby area
- Short range activator stimulates its on growth
- Results in specialised clusters of cells
Describe notch signalling
- Where a cell becomes differentiated due to tiny difference in protein levels and inhibits cells around it from becoming said cell in a self-amplifying process
- The same signal can also induce different responses. Either by combining with different signals or cells can ‘remember’ what signals they received earlier in their life and this can affect their differentiation in the future
How are acidians used as a model for cell fate?
- Every single cell in their bodies can be counted and cells will develop in exactly the same way across all organisms. Can produce a ‘lineage tree’
- Cell identity can also be defined by combinations of expression of transcription factors and ligands for a particular stage
How do FGF and ephrin work?
FGF signalling and Ephrin signalling on both sides of the embryo (animal and vegetal) define cell types later in life
What is cell sorting?
The formation of cell compartments which constrain signalling and cell movement to certain areas, forming units in which further differentiation can occur
What are the 3 mechanisms of cell sorting?
- heterophilic/homophilic interactions between cell adhesion molecules
- differential adhesion causing mixed aggregate to cluster and separate
- Maintenance of sharp boundaries by signalling
How does wnt function in relation to cell sorting?
uses b caterin which also binds to E-cadherin at membranes and the nucleus, which can physically link the cytoskeleton with what’s happening in the nucleus or affect transcription.
What are stem cells?
Cells which are undifferentiated, have the ability to self-renew and also are capable of differentiation
How are stem cells used in adult humans?
use resident lineage restricted stem cells for cell renewal & regeneration e.g hematopoetic stem cells which divide by a hierarchical process of restricting cell potency
What are the different stem cell potencies ordered from most potent to least potent?
Totipotent > Multipotent > Unipotent
What are stem cells affected by?
Niche, environment and aging
How do villi in the intestinal crypt constantly replenish themselves?
- Base contains paneth cells with transient amplifying proliferative cells zone (high in wnt)
- As cells move away start to differentiate less and be less influenced by wnt and more by BMP
- Ephrin responsible for maintaining compartmentalised zones
What happens when there is an overactivation of wnt in the gut?
produce too many crypt cells resulting in colon cancer
How do we know that gut stem cells are very potent?
LGR5 stem cell cultured on its own will form its own ‘mini-gut’
