Growth and Development
The Reverend Dr. David CM Taylor
dcmt@liverpool.ac.ukThis page is © David Taylor and The University of Liverpool, 1999
What is the problem?
The nervous system is complex
All cells carry the same genes
So how do the nerve cells know where they should grow
And how do the nerve cells know they are in the right place
Two (three) hypotheses
Cell fate
are distinct attributes of cell types specified independently
positional value
do the cells attributes depend on where they are
or both
would a neurone rather die than be without positional information?
Put another (slightly different)way
Are the different attributes specified sequentially or simultaneously.
Most striatal neurones are stellate in shape and GABAergic
Are the cells told that or do they work it out?
Homeobox genes - insects
Of course this is a false antithesis, but…
Most of the work is done in Drosophila
Drosophila have a series of genes that control different regions of the developing body.
If one of these homeobox genes malfunctions, then you see abnormalities.
Homeobox genes - mammals
Mammals have homeobox genes, but results of mutation/ deletion experiments in mammals have been less predictable than in Drosophila
But certain genes are more likely to be expressed in some regions of the CNS rather than others
"Gain of function"
Once a cell is located in a particular part of the CNS it seems that its near neighbours (glial cells?) have an influence on what it does.
Purves
Think about a tadpole/frog
When it starts its life it is tadpole shaped
Later it is frog shaped, and yet it still can identify which part of the skin is stimulated.
This is despite its change in both shape and size.
How?
Dale Purves suggests that it is because the nerves secrete and receive "growth factors" to and from the skin.
But the chemical signal alone is insufficient, there must be coincident electrical activity.
Recently we have learnt that this happens in the spinal cord as well.
So?
The phenomenon of plasticity is phenomenally important.
It allows learning, recovery from injury, growth and development.
Cell death is also important in preventing us from maintaining all sorts of inappropriate neuronal attachments