Stem cells & Development

Question 1

Define differentiation

Answer 1

The process by which a cell undergoes a change to an overtly specialised cell type

Question 2

What is determination?

Answer 2

Progressive restriction in developmental potential of different cell types through a cell’s pre-determined ‘fate’

Question 3

When can we say that a cell has become determined?

Answer 3

when cells are moved to a different location continue to develop into their fate regardless

Question 4

When is a cell specified?

Answer 4

• When isolated cells/tissues still form what they were originally meant to
• This means that the information needed is inherent

Question 5

Define induction

Answer 5

Process by which one embryonic region interacts with a second region to influence that second region’s differentiation or behavior

Question 6

What are the 3 types of cell signal?

Answer 6

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

Question 7

Give an example of induction

Answer 7

If animal cap cells are transplanted on to vegetal cells this induces the development of mesodermal tissue

Question 8

What is competence

Answer 8

Whereby cells may only be able to transmit/receive signals for a short space of time

Question 9

How do sea urchin studies show that the position of cells during early development is important?

Answer 9

• 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

Question 10

What is mosaic development?

Answer 10

Also known as ‘determinate’

When the separation of blastomeres results in incomplete parts of embryos and development is usually arrested

Question 11

How can cell division differentiate cells?

Answer 11

• Uneven distribution of protein/RNA during cell replication can lead to inherent differences between cells
• Asymmetric cell division can also differentiate cells

Question 12

Why is timing important?

Answer 12

Because even though early stages of development are regulative, lineages can become determined and invariant (animal and vegetal pole develop differently when isolated)

Question 13

Give 6 tissue patterning signals

Answer 13

1. Wnt
2. TGFb
3. BMP
4. Hh
5. Notch
6. RTK
   (Used by all multicellular organisms)

Question 14

What is a morphogen?

Answer 14

A substance whose gradient/exposure time across tissues causes differences in differentiation

Question 15

Describe the process of lateral inhibition

Answer 15

• 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

Question 16

Describe notch signalling

Answer 16

• 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

Question 17

How are acidians used as a model for cell fate?

Answer 17

• 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

Question 18

How do FGF and ephrin work?

Answer 18

FGF signalling and Ephrin signalling on both sides of the embryo (animal and vegetal) define cell types later in life

Question 19

What is cell sorting?

Answer 19

The formation of cell compartments which constrain signalling and cell movement to certain areas, forming units in which further differentiation can occur

Question 20

What are the 3 mechanisms of cell sorting?

Answer 20

• heterophilic/homophilic interactions between cell adhesion molecules
• differential adhesion causing mixed aggregate to cluster and separate
• Maintenance of sharp boundaries by signalling

Question 21

How does wnt function in relation to cell sorting?

Answer 21

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.

Question 22

What are stem cells?

Answer 22

Cells which are undifferentiated, have the ability to self-renew and also are capable of differentiation

Question 23

How are stem cells used in adult humans?

Answer 23

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

Question 24

What are the different stem cell potencies ordered from most potent to least potent?

Answer 24

Totipotent > Multipotent > Unipotent

Question 25

What are stem cells affected by?

Answer 25

Niche, environment and aging

Question 26

How do villi in the intestinal crypt constantly replenish themselves?

Answer 26

- 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

Question 27

What happens when there is an overactivation of wnt in the gut?

Answer 27

produce too many crypt cells resulting in colon cancer

Question 28

How do we know that gut stem cells are very potent?

Answer 28

LGR5 stem cell cultured on its own will form its own 'mini-gut'