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Figure 4.3 Inhibiting Rho associated kinase partially rescues ephrin-A5 induced growth
cone collapse. (A) Time-lapse stills of a RGC growth cone in the presence of 10 mM
Y27632. Times shown are times after addition of ephrin. (B) RGC growth cones fixed and
stained with phalloidin can be placed into one of three categories according to their
filamentous actin distribution, as shown in the right-hand panels. A full growth cone is
defined as consisting full lamella and filopodia. A partial growth cone has no lamella but
has three or more filopodia. Full collapse is defined as loss of both lamella and filopodia.
Cells were fixed after 10min stimulation with soluble ephrin-A5
As mentioned previously, ephrin molecules are membrane bound limiting
Eph receptor-ephrin interaction to sites of cell-cell contact. We have
developed a co-culture assay in which we can study the interaction of RGC
growth cones with cells expressing ephrin molecules on their surface. When a
RGC growth cone encounters an ephrin-A-expressing fibroblast cell in culture
the growth cone withdraws its lamella and the axon retracts within 10min
(Figure 4.4A). The fibroblast appears also to respond to the cell contact by
rapid lamella collapse (see Figure 4.4B). In other examples, a migrating
fibroblast will respond to the encounter by changing the direction of its
migration (data not shown). This demonstrates the bi-directional signalling
upon Eph receptor-ephrin activation at sites of cell-cell contact observed in
other systems.
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