Lecture Notes

Mechanism of axonal pathfinding
Attractive signal: Microfilaments and microtubules accumulate at the contact side

 The axon of the neuron need to find their target.
 Axons have a specific structure at the end
 Finger-like structure called fillopodia




Mechanisms of axonal pathfinding

 Stereotropism – physical barriers:
- Chanels and tunnels
 Haptotaxis – movement along substrate bound molecules:
a) molecules of the extracellular matrix and cell surface molecules
b) Selective fasciculation of axons: ‘‘labelled pathways“ hypothese
 Chemotropism – diffusible factors

1. Stereotropism – physical barriers
 If have collagen network will see the axons growing
 Collagen fibres
 Plastic barrier
 Artificial substrate
 tunnel




2. Haptotaxis – movement of growth cones along substrate bound molecules

,  ECM: glycoproteins and proteoglycans
 Cells have surface molecules
 Depending on which molecule is expressed they can bind to other cells
 If the cell has a compatible molecule on the surface then can bind




Cell adhesion proteins control motility and guide forward movement

• Cell-Cell adhesion
• Classical Cadherins (E,N, P, VE), homophilic binding, associated with cytoskeleton (actin filaments) via catenins
• Ig family members (N-CAM, ICAM), homo- and heterophilic binding
• Cell-matrix adhesion
• Integrins (many types), heterophilic binding, associated with cytoskeleton (actin filaments) via talin, paxillin, filamin etc.
• Transmembrane proteoglycans (syndecans), heterophilic binding

Haptotaxis I: ECM-molecules facilitate or inhibit axonal
growth
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