Evolutionary Biology 9: Signals, molecules, genes 1

Question 1

Describe 3 types of cell specification

Answer 1

1) Autonomous specification
- cell fate independent of interactions with neighbouring cells
- Cell lineage

2) Conditional specification
- cell fate determined by interactions with neighbouring cells
- positional information

3) syncytial specification
- determined by factors in syncytium (in insects, plant endosperm)

Question 2

Processes governing autonomous specification? Conditional specification?

Answer 2

Autonomous: Fate governed by cytoplasmic determinants
- mRNAs, proteins etc. assymetrically apportioned to cells during cell division

Conditional: governed by interactions of surrounding cells
- cell fate changed by changing surrounding environment and therefore signals

Question 3

Explain the process of induction

- what is competence?

Answer 3

Induction has 2 components

Inducer
- cell/tissue that generates inductive signal

Responder
- cell/tissue influenced by signal

If a tissue can respond to an inducer, it is said to exhibit competence

Competence changes over time (influenced by gene expression)

Question 4

Example of induction?

Answer 4

Limb bud induction - limb buds give rise to limbs

• emerge in specific locations due to expression of localised induction signals
• cause thickening of mesoderm and ectoderm from which limbs emerge

Limb bud induction can be stimulated in salamander embryos by grafting olfactory/otic placode onto region between forelimb and hindlimb
-> extra limb forms

Question 5

What did Tickle’s experiment in 1995 discover?

Answer 5

That FGFs (fibroblast growth factors) act as limb inducers
- all you need to make mesoderm sprout limbs is this inductive signal

Question 6

2 basic ways inducers act with responders?

Answer 6

Juxtacrine signalling
- signalling only between adjacent cells in contact

Paracrine signalling
- signalling across field of cells within close range

Question 7

Classic example of juxtacrine signalling?

Answer 7

Delta notch signalling

DELTA is a cell surface protein which acts as ligand for NOTCH (another cell surface protein)

both membrane bound so only juxtaposed cells can interact

when DELTA binds NOTCH, latter cleaved by proteases ADAM and PRESENILIN 1

liberates intracellular domain of NOTCH -> goes on to act as transcriptional regulator

Can control cell
division
specification
fate
differentiation

Question 8

Describe neurogenesis in zebrafish

Answer 8

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