Local Arp2/3-dependent actin assembly modulates applied traction force during apCAM adhesion site maturation.

Homophilic binding of immunoglobulin superfamily molecules such as the Aplysia cell adhesion molecule (apCAM) leads to actin filament assembly near nascent adhesion sites. Such actin assembly can generate significant localized forces that have not been characterized in the larger context of axon growth and guidance. We used apCAM-coated bead substrates applied to the surface of neuronal growth cones to characterize the development of forces evoked by varying stiffness of mechanical restraint.

Elastic coupling of nascent apCAM adhesions to flowing actin networks.

Adhesions are multi-molecular complexes that transmit forces generated by a cell's acto-myosin networks to external substrates. While the physical properties of some of the individual components of adhesions have been carefully characterized, the mechanics of the coupling between the cytoskeleton and the adhesion site as a whole are just beginning to be revealed. We characterized the mechanics of nascent adhesions mediated by the immunoglobulin-family cell adhesion molecule apCAM, which is known to interact with actin filaments.

Direct cAMP signaling through G-protein-coupled receptors mediates growth cone attraction induced by pituitary adenylate cyclase-activating polypeptide.

Developing axons are guided to their appropriate targets by environmental cues through the activation of specific receptors and intracellular signaling pathways. Here we report that gradients of pituitary adenylate cyclase-activating polypeptide (PACAP), a neuropeptide widely expressed in the developing nervous system, induce marked attraction of Xenopus growth cones in vitro. PACAP exerted its chemoattractive effects through PAC1, a PACAP-selective G-protein-coupled receptor (GPRC) expressed at the growth cone.

Growth cone turning induced by direct local modification of microtubule dynamics.

Pathfinding by nerve growth cones depends on attractive and repulsive turning in response to a variety of guidance cues. Here we present direct evidence to demonstrate an essential and instructive role for microtubules (MTs) in growth cone steering. First, both growth cone attraction and repulsion induced by diffusible cues in culture can be completely blocked by low concentrations of drugs that specifically inhibit dynamic microtubule ends in the growth cone.