Adhesion Dependent Growth

External beads couple to internal actin filament dynamics

Growth cone interaction with a native target  
Externally applied beads stick to the membrane and are transported by the movement of internal actin filaments.
Growth cone is transiently treated with cytochalasin
which turns off actin filament assembly. Note that linear
bead transport depends on actin filament assembly.
A growth cone undergoes a permissive target interaction with a neurite in cell culture. After articulating a right turn, the growth cone rapidly moves down the track defined by the neurite. This axon bundling process is called fasiculation  

Growth interaction with a restrained apCAM coated bead

Actin flow during growth cone-target interaction

apCAM is a homophilic Ig Superfamily molecule related to vertebrate NCAM. Here, a glass bead coated with
recombinant apCAM is being used as a pseudo-target
that elicits a response similar to growth cone interactions
with native target substrates.
Two growth cones interact in vitro. Color coded actin flow vectors are shown.

Actin dynamics during growth apCAM-bead interaction

Actin flow dynamics during apCAM bead interaction


A bead coated with an Ig superfamily cell adhesion molecule
was placed on a neuronal growth cone and restrained with a micro-needle to allow traction forces between the bead
and growth cone to develop. DIC image of stucture and fluorescently tagged actin filament are shown on right
and left, respectively.
Actin flow dynamics quantified for the growth cone target interaction shown to the left. Color velocity code as above.