Biology Reference
In-Depth Information
FIGURE 26.9
An explanation of the behaviour of the model. (a) In a round island, concentration of chemo-
attractant follows a Gaussian-like curve. (b) Cells therefore exert an inward pressure. (c) In the absence of contact
inhibition, bulk cells displaced outwards by the creation of a fjord in the edge (open arrows) push back up-gradient,
creating a pressure that tends to squeeze the fjord back out again despite the attempts of the cells at its tip to
advance. (d) In the presence of contact inhibition, however, the cells at the surface of the fjord show motility, but the
bulk cells that are displaced 'do not care', as they are unable to show a motile response to the chemotactic gradient.
the model associated with deviation from an ideal surface area), retraction of its exposed
edge will result in the inward-facing part of the cell exerting a pressure inwards (increasing
the probability of an advance in this direction). Along a perfectly round island, edge cells will
all exert an inwards pressure at right angles to the edge (
Figure 26.9
b).
Where there is
no
contact inhibition, the roundness of the island will be stable. This can be
understood by considering what would happen if, for some random reason, a small inden-
tation or 'fjord' were to form (
Figure 26.9
c). Cells at the front of the fjord would keep
'wanting' to advance, up-gradient, but the many cells that they would displace outwards
would also 'want' to move back towards the middle of the culture. Their pressure would
squeeze the fjord back out.
If cells surrounded by other cells
do
experience contact inhibition of motility, the self-
corrective opposition of rough edges is lost and smooth islands become unstable. Bulk cells
