Cell biological studies of neurite outgrowth: Fasciclin I and II, dynamin, and PAK

Responding to attractive and repulsive cues, axonal growth is directed to specific targets to form a functional neural circuitry. Chromophore-assisted laser inactivation (CALI) is a pioneering technique for the in situ inactivation of a target protein's function with a high degree of spatial and temporal resolution. Here, we have used CALI to study the function of adhesion molecules and signal transduction components in neurite outgrowth.;CALI was used to investigate the function of the neural cell adhesion molecules fasciclin I and II in the development of the grasshopper Ti1 neurons. Micro-CALI of fasciclin I results in defasciculation of Ti1 axons. The initial point of axon separation corresponds to the site of irradiation and defasciculation always continues distal to this point. Large scale and micro-CALI of fasciclin II perturbs Ti1 neuritogenesis but not fasciculation. This effect is restricted to a period during which cytoskeletal components and organelles are recruited to the site of neurite emergence.;Asymmetric micro-CALI of the protein phosphatase calcineurin in growth cones has previously established a role for calcineurin in mediating directed growth cone motility raising the possibility that the calcineurin substrate dynamin I plays a role in this process (Chang et al, 1995). Here, the potential role of the GTPases dynamin I and II in growth cone dynamics was investigated by micro-CALI of these proteins in cultured neurons. This study does not support a role for the dynamins in directed growth cone motility.;In fibroblasts, Cdc42, Rac1, and RhoA act in a cascade to induce filopodia, lamellipodia, and actin stress fibers, respectively (Nobes and Hall, 1995). These dynamic structures of the fibroblast are similar to those of the neural growth cone. Among the downstream effectors of Cdc42 and Rac1 is the p21...