Journal of Neuroscience, Vol 9, 2687-2696, Copyright © 1989 by Society for Neuroscience
Pioneer growth cone adhesion in vivo to boundary cells and neurons after enzymatic removal of basal lamina in grasshopper embryos
ML Condic and D Bentley
Neurobiology Group, University of California, Berkeley 94720.
The Ti1 pioneer neurons of embryonic grasshopper limbs extend axons between
the limb epithelium and its basal lamina. Their growth cones exhibit high
affinity for both limb segment boundaries and immature neurons. We have
investigated the role of the basal lamina in growth cone adhesion to
neurons and segment boundaries by removing the basal lamina with mild
enzymatic digestion when the Ti1 growth cones are in contact with different
cellular substrates. If the basal lamina is removed when the Ti1 growth
cones are in contact with other neurons, the growth cones remain in contact
with the neuronal somata, and the Ti1 cell bodies in contact with the
neuronal somata, and the Ti1 cell bodies reposition proximally. This
suggests that the basal lamina is involved in the adhesion of the Ti1
somata to the substrate but not in growth cone-neuronal adhesion. This is
the first direct evidence that growth cones establish adhesive cell-cell
interactions with other neurons in vivo. Enzymatic treatments that remove
the basal lamina also cause embryonic limbs to elongate. If the Ti1 axons
are strongly apposed to 2 segment boundaries prior to protease treatment,
their somata reposition to the nearest segment boundary, yet their axons do
not retract off of the segment boundaries, despite severe stretching by the
enzyme-induced limb expansion. These results indicate that the affinity of
the Ti1 cells for segment boundaries is due at least in part to adhesive
cell-cell interactions that are resistant to proteolytic digestion and
independent of the basal lamina.
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