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J. Cell Biol.,
Volume 141, Number 1, April 6, 1998 227-240
Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut 06520
Dynamic cytoskeletal rearrangements are involved in neuronal growth cone motility and guidance.
To investigate how cell surface receptors translate guidance cue recognition into these cytoskeletal changes,
we developed a novel in vitro assay where beads,
coated with antibodies to the immunoglobulin superfamily cell adhesion molecule apCAM or with purified
native apCAM, replaced cellular substrates. These
beads associated with retrograde F-actin flow, but in
contrast to previous studies, were then physically restrained with a microneedle to simulate interactions
with noncompliant cellular substrates. After a latency
period of ~10 min, we observed an abrupt increase in
bead-restraining tension accompanied by direct extension of the microtubule-rich central domain toward sites of apCAM bead binding. Most importantly, we
found that retrograde F-actin flow was attenuated only
after restraining tension had increased and only in the
bead interaction axis where preferential microtubule
extension occurred. These cytoskeletal and structural changes are very similar to those reported for growth
cone interactions with physiological targets. Immunolocalization using an antibody against the cytoplasmic domain of apCAM revealed accumulation of the transmembrane isoform of apCAM around bead-binding
sites. Our results provide direct evidence for a mechanical continuum from apCAM bead substrates through
the peripheral domain to the central cytoplasmic domain. By modulating functional linkage to the underlying actin cytoskeleton, cell surface receptors such as
apCAM appear to enable the application of tensioning
forces to extracellular substrates, providing a mechanism for transducing retrograde flow into guided
growth cone movement.
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