Biology Reference
In-Depth Information
FIGURE 11.4
(a) Semi-quantitative method for measuring cell adhesion, in which a fluid jet is used to loosen
cells. (b) Growth cones cross boundaries between equally adhesive substrates but avoid crossing from a more
adhesive to a less adhesive substrate.
A similar set of boundaries can be made by shining ultra-violet light through a metal grid
on to laminin, to produce lanes of native laminin that separate UV-denatured laminin.
Neurites remain on or move on to the native molecule and stick to it much more strongly
(as assessed by the shear force required to pull them away).
5
Direct and local interference with cell-substrate adhesion can be used to steer growth
cones. Cultured embryonic chick parasympathetic neurons produce axons with very wide
growth cones. If a fine glass needle is used to lift one side off the substrate, the growth
cone responds by extending away from the needle as would be predicted by haptotaxis.
This can be used to steer the growing axon in arbitrary shapes. Similarly, if a needle is
used to lift the very middle of a growth cone, each of the sides continues to advance so
that the growth cone, and hence the axon, bifurcates
6
(
Figure 11.5
).
FIGURE 11.5
Breaking the adhesion between the substrate and just one part of a growth cone, using a fine
needle, causes that part of the growth cone to stop advancing while other parts continue, just as the haptotaxis
hypothesis predicts.
